U.S. patent application number 15/446530 was filed with the patent office on 2018-09-06 for driver circuit for automatic detection and synchronization of dynamic loads.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Adolfo De Cicco, Maurizio Galvano, Roberto Penzo, Enrico Tonazzo.
Application Number | 20180255613 15/446530 |
Document ID | / |
Family ID | 63170972 |
Filed Date | 2018-09-06 |
United States Patent
Application |
20180255613 |
Kind Code |
A1 |
Galvano; Maurizio ; et
al. |
September 6, 2018 |
DRIVER CIRCUIT FOR AUTOMATIC DETECTION AND SYNCHRONIZATION OF
DYNAMIC LOADS
Abstract
An example method for preventing overcurrent in light-emitting
diode (LED) chains comprises deactivating a current regulation
control loop connected to a plurality of LED chains; regulating,
via a voltage regulation control loop, a forward voltage of the
plurality of LED chains; upon determining that a forward voltage of
the plurality of LED chains is equal to a target operating voltage
for a subset of the plurality of LED chains, bypassing at least one
of the plurality of LED chains such that only the subset of the
plurality of LED chains is connected to the current regulation
control loop; and upon determining that an output current of the
subset of the plurality of LED chains is equal to a target
operating current for the subset of the plurality of LED chains:
deactivating the voltage regulation control loop; and activating
the current regulation control loop.
Inventors: |
Galvano; Maurizio; (Padova,
IT) ; De Cicco; Adolfo; (Castel d'Azzano (VR),
IT) ; Penzo; Roberto; (Vigonza (PD), IT) ;
Tonazzo; Enrico; (Villanova di Camposampiero (PD),
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
63170972 |
Appl. No.: |
15/446530 |
Filed: |
March 1, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/10 20200101;
H05B 45/395 20200101; B60Q 1/34 20130101; B60Q 11/00 20130101; B60Q
1/1423 20130101; H05B 45/50 20200101; H05B 45/37 20200101; H05B
45/48 20200101 |
International
Class: |
H05B 33/08 20060101
H05B033/08; B60Q 1/14 20060101 B60Q001/14; B60Q 1/34 20060101
B60Q001/34 |
Claims
1. A method for preventing overcurrent when bypassing at least one
LED chain of a plurality of light-emitting diode (LED) chains
connected in series comprising: deactivating a current regulation
control loop, wherein the current regulation control loop is
connected to the plurality of LED chains in series; regulating, via
a voltage regulation control loop connected to the plurality of LED
chains, a forward voltage of the plurality of LED chains; upon
determining that the forward voltage of the plurality of LED chains
is equal to a target operating voltage for a subset of the
plurality of LED chains, bypassing the at least one of the
plurality of LED chains such that only the subset of the plurality
of LED chains is connected to the current regulation control loop
and the voltage regulation control loop; and upon determining that
an output current of the subset of the plurality of LED chains is
equal to a target operating current for the subset of the plurality
of LED chains: deactivating the voltage regulation control loop;
and activating the current regulation control loop.
2. The method of claim 1, wherein determining that the output
current of the subset of the plurality of LED chains is equal to
the target operating current comprises: sensing, via a
microcontroller, the output current of the subset of the plurality
of LED chains; and determining, via the microcontroller, that the
output current is equal to the target operating current.
3. The method of claim 1, wherein determining that the output
current of the subset of the plurality of LED chains is equal to
the target operating current comprises: sensing, via a changed load
detector circuit, an output current of the plurality of LED chains;
storing, via a sample and hold circuit of the changed load detector
circuit, a value of the sensed output current of the plurality of
LED chains; and comparing, via a comparator of the changed load
detector circuit, the stored value to an output current of the
subset of the plurality of LED chains.
4. The method of claim 1, wherein regulating the forward voltage of
the plurality of LED chains comprises: dynamically adjusting a
ratio of reference resistors such that the current regulation
control loop operates at a lower reference point; sensing a first
output current of the current regulation control loop; sensing a
second output current of the voltage regulation control loop;
determining a minimum of the first output current and the second
output current; and regulating the forward voltage of the plurality
of LED chains via one of the current regulation control loop and
the voltage regulation control loop based on the determined minimum
of the first output current and the second output current.
5. The method of claim 1, wherein one of a DC-DC current regulator
or a linear current regulator comprises the current regulation
control loop.
6. The method of claim 1, wherein the plurality of LED chains
provides a plurality of different functions for a vehicle
illumination system.
7. The method of claim 6, wherein: a first LED chain of the
plurality of LED chains provides high-beam headlight functionality
for the vehicle illumination system; a second LED chain of the
plurality of LED chains provides low-beam headlight functionality
for the vehicle illumination system; a third LED chain of the
plurality of LED chains provides corner light functionality for the
vehicle illumination system; a fourth LED vehicle illumination
system of the plurality of LED chains provides daytime running
light functionality for the vehicle; and a fifth LED chain of the
plurality of LED chains provides positioning light functionality
for the vehicle illumination system.
8. A driver circuit for preventing overcurrent when bypassing at
least one LED chain of a plurality of light-emitting diode (LED)
chains, configured to: deactivate a current regulation control
loop, wherein the current regulation control loop is connected to a
plurality of light-emitting diode (LED) chains; regulate, via a
voltage regulation control loop connected to the plurality of LED
chains, a forward voltage of the plurality of LED chains; upon
determining that [[a]] the forward voltage of the plurality of LED
chains is equal to a target operating voltage for a subset of the
plurality of LED chains, bypass the at least one LED chain of the
plurality of LED chains such that only the subset of the plurality
of LED chains is connected to the current regulation control loop
and the voltage regulation control loop; and upon determining that
an output current of the subset of the plurality of LED chains is
equal to a target operating current for the subset of the plurality
of LED chains: deactivate the voltage regulation control loop; and
activate the current regulation control loop.
9. The driver circuit of claim 8, wherein the driver circuit
comprises a microcontroller configured to: sense the output current
of the subset of the plurality of LED chains; and determine that
the output current is equal to the target operating current.
10. The driver circuit of claim 8, wherein the driver circuit
further comprises: a changed load detector circuit configured to
sense an output current of the plurality of LED chains; a sample
and hold circuit of the changed load detector circuit configured to
store a value of the sensed output current of the plurality of LED
chains; and a comparator of the changed load detector circuit
configured to compare the stored value to an output current of the
subset of the plurality of LED chains.
11. The driver circuit of claim 8, wherein the driver circuit is
further configured to: dynamically adjust a ratio of reference
resistors such that the current regulation control loop operates at
a lower reference point; sense a first output current of the
current regulation control loop; sense a second output current of
the voltage regulation control loop; determine a minimum of the
first output current and the second output current; and regulate
the forward voltage of the plurality of LED chains via one of the
current regulation control loop and the voltage regulation control
loop based on the determined minimum of the first output current
and the second output current.
12. The driver circuit of claim 8, wherein one of a DC-DC current
regulator or a linear current regulator comprises the current
regulation control loop.
13. The driver circuit of claim 8, wherein the plurality of LED
chains provides a plurality of different functions for a vehicle
illumination system.
14. A system for preventing overcurrent when bypassing at least one
LED chain of a plurality of light-emitting diode (LED) chains
connected in series comprising: a driver circuit, configured to:
deactivate a current regulation control loop, wherein the current
regulation control loop is connected to the plurality of LED
chains; regulate, via a voltage regulation control loop connected
to the plurality of LED chains, a forward voltage of the plurality
of LED chains; upon determining that the forward voltage of the
plurality of LED chains is equal to a target operating voltage for
a subset of the plurality of LED chains, bypass the at least one
LED chain of the plurality of LED chains such that only the subset
of the plurality of LED chains is connected to the current
regulation control loop and the voltage regulation control loop;
and upon determining that an output current of the subset of the
plurality of LED chains is equal to a target operating current for
the subset of the plurality of LED chains: deactivate the voltage
regulation control loop; and activate the current regulation
control loop; and the plurality of LED chains.
15. The system of claim 14, wherein the driver circuit comprises a
microcontroller configured to: sense the output current of the
subset of the plurality of LED chains; and determine that the
output current is equal to the target operating current.
16. The system of claim 14, wherein the driver circuit further
comprises: a changed load detector circuit configured to sense an
output current of the plurality of LED chains; a sample and hold
circuit of the changed load detector circuit configured to store a
value of the sensed output current of the plurality of LED chains;
and a comparator of the changed load detector circuit configured to
compare the stored value to an output current of the subset of the
plurality of LED chains.
17. The system of claim 14, wherein the driver circuit is further
configured to: dynamically adjust a ratio of reference resistors
such that the current regulation control loop operates at a lower
reference point; sense a first output current of the current
regulation control loop; sense a second output current of the
voltage regulation control loop; determine a minimum of the first
output current and the second output current; and regulate the
forward voltage of the plurality of LED chains via one of the
current regulation control loop and the voltage regulation control
loop based on the determined minimum of the first output current
and the second output current.
18. The system of claim 14, wherein one of a DC-DC current
regulator or a linear current regulator comprises the current
regulation control loop.
19. The system of claim 14, wherein the plurality of LED chains
provides a plurality of different functions for a vehicle
illumination system.
20. The driver circuit of claim 19, wherein: a first LED chain of
the plurality of LED chains provides high-beam headlight
functionality for the vehicle illumination system; a second LED
chain of the plurality of LED chains provides low-beam headlight
functionality for the vehicle illumination system; a third LED
chain of the plurality of LED chains provides corner light
functionality for the vehicle illumination system; a fourth LED
vehicle illumination system of the plurality of LED chains provides
daytime running light functionality for the vehicle; and a fifth
LED chain of the plurality of LED chains provides positioning light
functionality for the vehicle illumination system.
Description
TECHNICAL FIELD
[0001] This disclosure generally relates to driver circuits for
light-emitting diode (LED) applications.
BACKGROUND
[0002] Some applications in automotive lighting or other
applications involve a plurality of LED chains, each including a
number of LEDs connected in series. The number may vary depending
on the specific application. One or more of the LEDs can be
bypassed at times, temporarily reducing the length of the LED
chain. A DC/DC converter may control the current flowing through
the LED chain as different numbers of the LEDs in the chain are
used, while the output voltage is set by the number and the forward
voltage of the LEDs that compose the chain.
SUMMARY
[0003] In general, the disclosure describes techniques, methods,
devices, and systems for preventing overcurrent in one or more LED
chains connected in series when bypassing at least one LED chain of
the one or more LED chains connected in series. A driver circuit
for one or more LED chains comprises a closed loop current
regulator, such as a DC-DC current regulator or a linear current
regulator, that functions to control the intensity of the LED chain
by adjusting the amount of current flowing through the LED chain.
The driver circuit for one or more LED chains further comprises a
voltage regulation control loop which is activated in response to
an external command to reach and maintain the desired voltage value
and a sample & hold circuit to store the load current value
when reaching the new target output voltage. When one or more LED
chains are going to be bypassed, the driver circuit deactivates the
current regulator and activates the voltage regulation control
loop. When the target output voltage is reached, the one or more
LED chains may be bypassed. Upon detecting that the output current
has risen to an expected output current for the remaining one or
more LED chains, the driver circuit deactivates the voltage
regulation control loop and re-activates the current regulation
control loop.
[0004] In one example, this disclosure describes a method
including: deactivating a current regulation control loop, wherein
the current regulation control loop is connected to a plurality of
light-emitting diode (LED) chains in series; regulating, via a
voltage regulation control loop connected to the plurality of LED
chains, a forward voltage of the plurality of LED chains; upon
determining that a forward voltage of the plurality of LED chains
is equal to a target operating voltage for a subset of the
plurality of LED chains, bypassing at least one of the plurality of
LED chains such that only the subset of the plurality of LED chains
is connected to the current regulation control loop and the voltage
regulation control loop; and upon determining that an output
current of the subset of the plurality of LED chains is equal to a
target operating current for the subset of the plurality of LED
chains: deactivating the voltage regulation control loop; and
activating the current regulation control loop.
[0005] In another example, this disclosure describes a driver
circuit for a plurality of light-emitting diode (LED) chains,
configured to: deactivate a current regulation control loop,
wherein the current regulation control loop is connected to a
plurality of light-emitting diode (LED) chains; regulate, via a
voltage regulation control loop connected to the plurality of LED
chains, a forward voltage of the plurality of LED chains; upon
determining that a forward voltage of the plurality of LED chains
is equal to a target operating voltage for a subset of the
plurality of LED chains, bypass at least one of the plurality of
LED chains such that only the subset of the plurality of LED chains
is connected to the current regulation control loop and the voltage
regulation control loop; and upon determining that an output
current of the subset of the plurality of LED chains is equal to a
target operating current for the subset of the plurality of LED
chains: deactivate the voltage regulation control loop; and
activate the current regulation control loop.
[0006] In another example, this disclosure describes a system
including: a driver circuit, configured to: deactivate a current
regulation control loop, wherein the current regulation control
loop is connected to a plurality of light-emitting diode (LED)
chains; regulate, via a voltage regulation control loop connected
to the plurality of LED chains, a forward voltage of the plurality
of LED chains; upon determining that a forward voltage of the
plurality of LED chains is equal to a target operating voltage for
a subset of the plurality of LED chains, bypass at least one of the
plurality of LED chains such that only the subset of the plurality
of LED chains is connected to the current regulation control loop
and the voltage regulation control loop; and upon determining that
an output current of the subset of the plurality of LED chains is
equal to a target operating current for the subset of the plurality
of LED chains: deactivate the voltage regulation control loop; and
activate the current regulation control loop; and the plurality of
LED chains.
[0007] The details of one or more examples of the techniques of
this disclosure are set forth in the accompanying drawings and the
description below. Other features, objects, and advantages of the
techniques will be apparent from the description and drawings, and
from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a block diagram illustrating an example driver
circuit for a plurality of LED chains in accordance with the
techniques of the disclosure.
[0009] FIG. 2 is a block diagram illustrating an example control
loop for the driver circuit of FIG. 1, in accordance with the
techniques of the disclosure.
[0010] FIG. 3 is a block diagram illustrating an example changed
load detector for the driver circuit of FIG. 1, in accordance with
the techniques of the disclosure.
[0011] FIG. 4A is a chart illustrating example signals of the
driver circuit of FIG. 1, in accordance with the techniques of the
disclosure.
[0012] FIG. 4B is a chart illustrating example signals of the
driver circuit of FIG. 1, in accordance with the techniques of the
disclosure.
[0013] FIG. 5 is a circuit diagram illustrating an example driver
circuit for a plurality of LED chains in accordance with the
techniques of the disclosure.
[0014] FIG. 6 is a circuit diagram illustrating an example control
loop for the driver circuit of FIG. 5, in accordance with the
techniques of the disclosure.
[0015] FIG. 7 is a flowchart illustrating an example operation of
the driver circuit for the plurality of LED chains of FIG. 1, in
accordance with the techniques of the disclosure.
DETAILED DESCRIPTION
[0016] A driver circuit for one or more LED chains comprises a
closed loop current regulator, such as a DC-DC current regulator or
a linear current regulator, that functions to control the intensity
of the LED chain by adjusting the amount of current flowing through
the LED chain. In some examples, the current regulator is
implemented via a current regulation control loop and a power
source. In other systems, such a driver circuit includes a
plurality of LED chains connected in series. Further, the driver
circuit comprises a plurality of bypass switches, wherein the
driver circuit may selectively activate each bypass switch to
bypass a corresponding one of the plurality of LED chains. Upon
activating one of the plurality of bypass switches to bypass a
corresponding LED chain, the driver circuit discharges the output
tank capacitor of the current regulator through the remaining LED
chains. The current flowing through the remaining LED chains is
limited only by the series resistances of the LEDs of the remaining
LED chains themselves. In some situations, the series resistance is
insufficient to prevent overcurrent, which may damage or reduce the
operating life of the LEDs of the remaining LED chains.
[0017] In other systems, to prevent overcurrent, prior to bypassing
the one or more LED chains, the driver circuit deactivates the
current regulator so as to stop the energy transfer to the
plurality of LED chains. The driver circuit allows the LED chains
to discharge the output capacitor to a desired voltage value,
wherein the desired voltage value is a target operating voltage for
the one or more remaining LED chains after bypassing the one or
more bypassed LED chains. However, this requires a microcontroller
of the driver circuit to continuously poll the output capacitor to
determine when the output capacitor reaches the desired voltage
value. Further, to prevent overcurrent, the driver circuit must
synchronize reactivating the current regulator and activating a
bypass switch to bypass the one or more LED chains. If the
reactivation of the current regulator does not occur simultaneously
with activating the bypass switch, the extra voltage induced by the
current regulator may cause an overcurrent through the one or more
LED chains, potentially causing damage to or decreasing the
operating life of the one or more LED chains.
[0018] According to the techniques of the disclosure, a driver
circuit for one or more LED chains further comprises a voltage
regulation control loop which is activated in response to an
external command to reach and maintain the desired voltage value
and a changed load detector to detect output current changes in the
one or more LED chains. Prior to bypassing the one or more LED
chains, the driver circuit of the present disclosure deactivates a
current regulation control loop and activates the voltage
regulation control loop to discharge the output capacitor to a
desired voltage value. The changed load detector triggers when the
output capacitor reaches a desired voltage value, which indicates
that voltage value is such that one or more LED chains may be
bypassed. The driver circuit activates a bypass switch to bypass
the one or more LED chains. Upon detecting, via the changed load
detector, that the output current has risen to an expected value
with respect to the stored value for the remaining one or more LED
chains, the driver circuit deactivates the voltage regulation
control loop and re-activates a current regulation control
loop.
[0019] FIG. 1 is a block diagram illustrating an example driver
circuit 100 for a plurality of LED chains 106 in accordance with
the techniques of the disclosure. Driver circuit 100 includes a
power source 101, that functions to deliver power to plurality of
LED chains 106. The driver circuit 100 further includes a current
regulation control loop 102 that, when connected to power source
101 and plurality of LED chains 106, functions as a DC-DC current
regulator or a linear current regulator, to control the intensity
of the plurality of LED chains 106 by regulating the amount of
current flowing through the plurality of LED chains 106. Driver
circuit 100 further includes a voltage regulation control loop 104
that, when connected to power source 101 and plurality of LED
chains 106, functions to maintain a constant forward voltage across
the plurality of LED chains 106. Driver circuit 100 further
includes a microcontroller 108 for controlling the various
circuitry of driver circuit 100.
[0020] Driver circuit 100 additionally includes a plurality of
bypass switches 110. Microcontroller 108 of driver circuit 100 may
selectively activate each bypass switch 110 to bypass a
corresponding one of the plurality of LED chains 106. In one
implementation, microcontroller 108 activates each bypass switch of
plurality of bypass switches 110 according to a unique duty cycle.
In this way, microcontroller 108 may selectively apply digital
modulation, such as pulse-width modulation (PWM), pulse-duration
modulation, or pulse-density modulation, for separate dimming of
each LED chain of plurality of LED chains 106.
[0021] In some examples, plurality of bypass switches 110 are a
single multi-floating switch. In this example, each switch of the
multi-floating switch is independently selectable, and is
controlled by microcontroller 108. In other examples, plurality of
bypass switches 110 are a plurality of transistors, such as
metal-oxide-semiconductor field-effect transistors (MOSFETs) or
bipolar junction transistors (BJTs). In some examples, plurality of
bypass switches 110 are power MOSFETs. In some examples, plurality
of bypass switches 110 are vertical bi-polar junction transistors
(BJTs). In other examples, plurality of bypass switches 110 are
vertical metal-oxide-semiconductor field effect transistors
(MOSFETs). In some examples, plurality of bypass switches 110 are
source-down or source-up transistors. In some examples, plurality
of bypass switches 110 are lateral MOSFETs. In some examples,
plurality of bypass switches 110 are lateral n-type channel MOSFETs
built on a p-type substrate. In some examples, plurality of bypass
switches 110 are lateral n-type channel MOSETs built on
Silicon-on-Insulator (SOI) substrate. In some examples, plurality
of bypass switches 110 are a cascode of an n-type channel
junction-gate field effect transistor (JFET) in series with a
low-voltage MOSFET. In some examples, plurality of bypass switches
110 are superjunction MOSFETs. In some examples, plurality of
bypass switches 110 have high switching speed and low gate charge.
In some examples, plurality of bypass switches 110 have low
capacitance from drain to source and from drain to substrate.
[0022] When driver circuit 100 activates one of the plurality of
bypass switches 110 to bypass a corresponding LED chain 106, the
output tank capacitor of the current regulation control loop 102
(not depicted) is discharged through the remaining LED chains 106.
Without using the techniques of the disclosure, the current flowing
through the remaining LED chains 106 is limited only by the series
resistances of the LEDs of the remaining LED chains 106 themselves.
The series resistance of the remaining LED chains 106 may be
insufficient to prevent overcurrent, which may damage or reduce the
operating life of the LEDs of the remaining LED chains.
[0023] In some examples, Microcontroller 108 is one or more
microprocessors, digital signal processors (DSPs), application
specific integrated circuits (ASICs), field programmable gate
arrays (FPGAs), or any other equivalent integrated or discrete
logic circuitry, as well as any combinations of such components.
Microcontroller 108 may include memory, which may be random access
memory (RAM), read only memory (ROM), programmable read only memory
(PROM), erasable programmable read only memory (EPROM),
electronically erasable programmable read only memory (EEPROM),
flash memory, comprising executable instructions for causing the
one or more processors to perform the actions attributed to them.
In some examples, this memory is on-board microcontroller 108,
while in other examples, this memory is externally coupled to
microcontroller 108. Further, this memory may be implanted entirely
in hardware, software, or a combination thereof.
[0024] The LEDs of the plurality of LED chains 106 may be any sort
of LED, such as organic LEDs (OLEDs), phosphor-based LEDs, Quantum
Dot LEDs (QD-LEDs), miniature LEDs, low-current LEDs, ultra-high
output LEDs, high-power LEDs, multi-color LEDs, or filament LEDs.
In some examples, LED 106 is a single LED. In other examples, LEDs
106 are a string of LEDs, a group of strings of LEDs, or an array
of LEDs.
[0025] Power source 101 delivers operating power to various
components of driver circuit 100. Power source 101 includes all of
the power circuitry to implement a linear or DC-DC regulator for
supplying power to the elements of driver circuit 100. In one
example, power source 101 further includes a rechargeable or
non-rechargeable battery, such as an Alkaline, Zinc-Carbon,
Lead-Acid, Mercury, Lithium Ion, Lithium Polymer, Silver Oxide,
Nickel-Cadmium, Nickel-Metal Hydride, or Nickel-Zinc battery. In
some examples, the battery is a vehicle battery and is recharged by
an alternator of the vehicle. In other examples, power source 101
includes circuitry for converting an alternating current (AC) power
source from a local utility into direct-current (DC) power for use
by driver circuit 100. In further examples, power source 101
includes a power generation circuit to produce the operating
power.
[0026] Current regulation control loop 102 is a closed-loop power
control circuit that operates to ensure that the current flowing
into plurality of LED chains 106 remains constant. In some
examples, when connected to power source 101, current regulation
control loop 102 functions as a DC-DC current regulator or a linear
current regulator. In some examples, current regulation control
loop 102 uses a pulse-width modulation signal to generate an output
current. Current regulation control loop 102 further includes a
feedback signal for regulating the output current. Current
regulation control loop 102 may have a faster response time than
voltage regulation control loop 104. Current regulation control
loop 102 may further eliminate loop-gain variation with input
voltage that occurs with some voltage regulation control loops.
[0027] In other systems, driver circuit 100 must synchronize
reactivating current regulation control loop 102 and activating one
of bypass switches 110 to bypass one or more LED chains of the
plurality of LED chains 106. If the reactivation of current
regulation control loop 102 does not occur simultaneously with
activating the corresponding bypass switch 110, the extra voltage
induced by current regulation control loop 102 may cause an
overcurrent through one or more of the remaining LED chains 106,
potentially causing damage to or decreasing the operating life of
the remaining LED chains 106.
[0028] According to the techniques of the disclosure, driver
circuit 100 further comprises a voltage regulation control loop
104. Voltage regulation control loop 104 is a closed-loop power
control circuit that operates to ensure that the forward voltage
across plurality of LED chains 106 remains constant. Typically,
voltage regulation control loop 104 uses a pulse-width modulation
(PWM) signal to generate the output voltage. In some examples, the
voltage regulation control loop 104 generates the PWM signal by
applying a control voltage to a first input of a comparator and a
saw tooth voltage signal having a fixed frequency to the second
input of the comparator. Thus, the duty cycle of the PWM signal is
proportional to the control voltage and determines the percentage
of the time that the switching element conducts, and in turn, the
value of the output voltage. As compared to current regulation
control loop 102, voltage regulation control loop 104 may have a
slower response time. However, in contrast to current regulation
control loop 102, voltage regulation control loop 104 operates to
maintain a constant voltage across plurality of LED chains 106. In
ordinary operation, driver circuit 100 drives the plurality of LED
chains 106 via current regulation control loop 102, while when
selectively enabling or disabling one or more of plurality of LED
chains 106, driver circuit 100 uses voltage regulation control loop
104 such that voltage regulation control loop 104 to regulate a
constant voltage across the plurality of LED chains 106 before the
number of active LEDs of plurality of LED chains 106 changes.
Therefore, driver circuit 100 may more closely synchronize the
delivery of power to plurality of LED chains 106 while dynamically
enabling and disabling one or more of LED chains 106. In contrast
to other systems that do not implement the techniques of the
disclosure, such a driver circuit 100 may avoid inducing
overcurrent plurality of LED chains 106, and prevent damage to or
decreasing the operating life of plurality of LED chains 106.
[0029] Further examples of current regulation control loop 102 and
voltage regulation control loop 104 may be found in U.S. Patent
App. Pub. 2016/0183337 to Galvano, et. al, entitled "ADAPTIVE
DIRECT CURRENT (DC) TO DC (DC-TO-DC) LEIGHT EMITTING DIODE (LED)
DRIVER FOR DYNAMIC LOADS)" and published on Jun. 23, 2016, the
content of which is incorporated herein in its entirety.
[0030] Driver circuit 100 may further include a changed load
detector 112. Changed load detector circuit 112 operates to detect
when the output current has risen in response to a deactivation of
one or more LED chains of plurality of LED chains 106, operated via
the plurality of bypass switches 110. Changed load detector 112
operates to store an output current value and compare it with the
real-time output current value. The output signal of the changed
load detector circuit 112 can be used to deactivate voltage
regulation control loop 104 and reactivate current regulation
control loop 102.
[0031] In some examples, changed load detector 112 includes a
Sample&Hold (S&H) circuit, which operates to store a target
current for a remaining plurality of LED chains 106 and acts as a
reference value to allow subsequent deactivating voltage regulation
control loop 104 and reactivating current regulation control loop
102. In some examples, the S&H circuit functions as an
Analog-to-Digital Converter (ADC) to convert an analog output
current flowing from plurality of LED chains 106 into a discrete
digital signal. In some examples, the S&H circuit is
implemented simply via a switch and a capacitor. In other examples,
the S&H circuit is implemented using a flip-flop. In still
further examples, the S&H circuit is implemented using one or
more discrete logic gates and circuits.
[0032] In an example operation to bypass one or more LED chains of
plurality of LED chains 106, microcontroller 108 deactivates
current regulation control loop 102 and activates voltage
regulation control loop 104. Upon doing so, the voltage across
plurality of LED chains 106 falls to a target operating voltage for
the remaining plurality of LED chains 106. Upon the voltage across
plurality of LED chains 106 reaches the target voltage changed load
detector 112 stores the value of the current flowing through
plurality of LED chains 106. Driver circuit 100 bypasses, via the
plurality of bypass switches 110, one or more of the plurality of
LED chains 106 such that only the remaining plurality of LED chains
106 receive power. The output current flowing through the remaining
plurality of LED chains 106 rises, and upon detecting, via the
changed load detector 112, that the output current has risen to an
expected value with respect to the stored value (e.g., the target
output current for the remaining plurality of LED chains 106),
driver circuit 100 deactivates voltage regulation control loop 104
and reactivates current regulation control loop 102.
[0033] In some examples, driver circuit 100 includes a comparator
(not depicted) for comparing the signal received from changed load
detector 112, which retains a target output current for the
remaining LED chains of the plurality of LED chains 106, to a
current flowing through the remaining LED chains. Microcontroller
108 may use the output of the comparator to determine when to
deactivate voltage regulation control loop 104 and reactivate
current regulation control loop 102. In the example of FIG. 1, the
functions of the comparator are performed by microcontroller 108.
In further examples, the functions of changed load detector 112 are
performed by microcontroller 108.
[0034] Such a driver circuit as described may be useful for
controlling a plurality of LED chains in a vehicle headlight
illumination system. As example, plurality of LED chains 106 are
connected in series, wherein each LED chain of the plurality of LED
chains 106 provides a particular function for the vehicle
illumination system. For example, a first LED chain provides
high-beam functionality, a second LED chain provides low-beam
functionality, a third LED chain provides corner light
functionality, a fourth LED chain provides daytime running light
(DRL) functionality, and a fifth LED chain provides positioning
light functionality. Other types of vehicles may have different
types of configurations as well.
[0035] The driver circuit described herein may be suitable for any
type of vehicle headlight illumination system, for example, such as
those used in automobiles, such as cars, trucks, and sport utility
vehicles (SUV), watercraft and ships, aircraft, military vehicles,
such as tanks, jeeps, and half-tracks, amphibious vehicles,
transportation vehicles, such as semi-trucks and trailers,
construction vehicles, such as bulldozers, tractors, backhoes, and
cranes, heavy machinery, trains, motorcycles, mopeds, recreational
vehicles such as golf carts, dune buggies, and all-terrain vehicles
(ATV), unpowered vehicles, such as bicycles, and many other types
of vehicles not explicitly described herein.
[0036] FIG. 2 is a block diagram illustrating an example control
loop 104 for the driver circuit 100 of FIG. 1, in accordance with
the techniques of the disclosure. Control loop 104 of FIG. 2 is an
example of the voltage regulation control loop 104 of FIG.1.
[0037] As shown, voltage control regulation loop 104 includes an
input port 230, voltage dividers 206A, 206B, a switch 205, a
comparator 202, an error amplifier 208, a switch 215, and an output
port 590.
[0038] Comparator 202 is a circuit that receives two inputs and
outputs a comparison of the two inputs. In some examples,
comparator 202 outputs a signal indicating which of the two inputs
is larger. In other examples, comparator 202 outputs a signal
indicating the magnitude of the difference.
[0039] Error amplifier 208 generates an error control signal
indicating a difference between a feedback signal and a target
reference. In some examples, error amplifier 208 is an operational
amplifier.
[0040] S&H circuit 212 may be implemented using a switch 205
and a capacitor 204. Capacitor 204 is any device that includes at
least two electrical conductors or plates that are separated by a
dielectric material such that the dielectric material stores energy
when polarized by an electrical field. In some examples, capacitor
204 is a ceramic capacitor, a film or power film capacitor, an
electrolytic capacitor, an integrated capacitor, a power capacitor,
or a variable capacitor. In some examples, the dielectric of the
capacitor comprises glass, ceramic, plastic film, air, vacuum,
paper, mica, or oxide layers.
[0041] The voltage control regulation loop 104 is adapted to
regulate power supply 101 from an initial output voltage to a
target output voltage by manipulating resistances of the voltage
dividers 206A, 206B in accordance with a ratio between an initial
load (e.g., the number of circuit elements in the chain prior to
changing the chain's length) and a final load (e.g., the number of
circuit elements in the chain after changing the chain's length).
The number of resistors in the voltage dividers 206A, 206B may be
equal to the max number of LEDs of plurality of LED chains 106 that
can be connected to the output. The voltage divider 206A represents
the load during the first period (e.g., a first number of LED
chains 106A of plurality of LED chains 106), and the voltage
divider 206B represents the target load at the beginning of the
second period (e.g., a second number of LED chains 106B of
plurality of LED chains 106). For example, if the load is being
decreased from four LEDs to three LEDs, then the voltage divider
206A connects four series-connected resistors and the voltage
divider 206B connects three series-connected resistors.
[0042] The input port 230 is configured to receive a feedback
signal (V.sub.FB) that is indicative of the output voltage of power
supply 101. For example, the feedback signal (V.sub.FB) indicates
that the output voltage is approximately equal to the initial
voltage at the beginning of the transition period. The feedback
signal then flows over the respective voltage dividers 206A, 206B,
after which the outputs of the voltage dividers 206A, 206B are
sampled to obtain a first sampled signal (V.sub.FB1). Opening
switch 205 stores the initial value of the first sampled signal in
the capacitor of S&H circuit 212, while closing the switch 215
allows an error correction signal from the error amplifier 208 to
regulate power supply 101.
[0043] The error correction signal has a magnitude that corresponds
to a difference between the initial value of the first sampled
signal (V.sub.FB1(n-1)) and the present value of the second sampled
signal (V.sub.FB2(n)). The output voltage of power supply 101 may
be reduced in accordance with the magnitude of the error correction
signal. For example, the output voltage of power supply 101 may be
reduced at a fixed rate so long as the magnitude of the error
correction signal exceeds a threshold. As another example, the
output voltage of power supply 101 may be reduced at a rate that is
proportional to the magnitude of the error correction signal, in
which case the rate of voltage regulation decreases as the output
voltage of the power supply approaches the target voltage.
[0044] Accordingly, such a voltage regulation control loop 104 may
allow a driver circuit 100 to more closely synchronize the delivery
of power to plurality of LED chains 106 while dynamically enabling
and disabling one or more of LED chains 106. In contrast to other
systems that do not implement the techniques of the disclosure,
such a driver circuit 100 may avoid inducing overcurrent plurality
of LED chains 106, and prevent damage to or decreasing the
operating life of plurality of LED chains 106.
[0045] FIG. 3 is a block diagram illustrating an example changed
load detector 112 for the driver circuit 100 of FIG. 1, in
accordance with the techniques of the disclosure. The example
changed load detector 112 operates to detect a changed load within
plurality of LED chains 106 of FIG. 1 (e.g., when the number of
selected LED chains of the plurality of LED chains 106 changes).
The comparator 202 and S&H circuit 212 may function in a
substantially similar fashion to the like elements of FIG. 2.
[0046] As depicted in FIG. 3, changed load detector 112 further
includes a current sense amplifier 302. Current sense amplifier 302
senses the voltage drop on a shunt resistor 106 (that is
proportional to LED current) and translates this in a voltage value
referred to ground. In some examples, current sense amplifier 302
is a component of current regulation control loop 102 and functions
to regulate the current flowing through plurality of LED chains
106.
[0047] S&H 212 receives, as an input, the output of current
sense amplifier 302, and stores the value when the voltage target
is reached. Comparator 202 receives, as a first input, the voltage
of the capacitor 204 (e.g., the stored value of S&H 212).
Comparator 202 uses the sampled voltage of capacitor 204 as an
inverting input, and comparator 202 receives, as a non-inverting
input, a partition of the voltage at the output of current sense
amplifier 302. Thus, comparator 202 continuously monitors the
output current of the plurality of LED chains 106 to determine
whether the output current increases over the sampled value. In
this fashion, comparator 202 may determine when microcontroller 108
activates one of the plurality of bypasses switch 110 and adjusts
the number of active LED chains of the plurality of LED chains 106.
A ratio .sub.R of resistor dividers 306 sets the threshold of
comparator 202. For example, when the output current of the
plurality of LED chains 106 is higher than the sampled current by a
factor 1/(3, the output of comparator 202 becomes high. The output
of comparator 202 may be used as to deactivate the voltage
regulation control loop and activate the current regulation control
loop again.
[0048] The changed load detector 112 of FIG. 3 is an example of the
changed load detector 112 of FIG. 1. Therefore, driver circuit 100
may more closely synchronize the delivery of power to plurality of
LED chains 106 while dynamically enabling and disabling one or more
of LED chains 106. In contrast to other systems that do not
implement the techniques of the disclosure, such a driver circuit
100 may avoid inducing overcurrent plurality of LED chains 106, and
prevent damage to or decreasing the operating life of plurality of
LED chains 106. Furthermore, the changed load detector 112 does not
require microcontroller 108 to continuously poll the output current
of the plurality of LED chains 106 to detect a change in the output
current or in the number of active LED chains 106. Thus, such a
driver circuit as described herein may implement automatic
synchronization between activating a bypass switch to bypass the
one or more LED chains and reactivating the current regulation
control loop.
[0049] FIG. 4A is a chart illustrating example signals of the
driver circuit 100 of FIG. 1, in accordance with the techniques of
the disclosure. In the example of FIG. 4A, driver circuit 100
drives a first number of active LED chains of the plurality of LED
chains 106. Subsequently, microcontroller 108 selectively activates
a second number of LED chains of the plurality of LED chains 106.
In this example, the second number of active LED chains has an
operating voltage that is less than the threshold voltage
(V.sub.TH) of the first number of active LED chains. By using the
techniques of the present disclosure, driver circuit 100 may
prevent overcurrent induced in the second number of active LED
chains, thus preventing damage or degradation in the second number
of active LED chains.
[0050] As depicted in FIG. 4A, at time t0, microcontroller
disconnects, via a switch, current regulation control loop 102 and
connects voltage regulation control loop 104. The connection status
of current regulation control loop 102 is depicted as line 408. At
this time, the output current 402 of current regulation control
loop 102 and the output current 404 flowing through the first
number of LED chains of the plurality of LED chains 106 falls.
Because voltage regulation control loop 104 is driving the forward
voltage 406 of the first number of LED chains of the plurality of
LED chains 106 to the lower target forward voltage for the second
number of LED chains, the forward voltage 406 similarly falls.
[0051] At time t1, the forward voltage 406 falls to the target
voltage. Upon the forward voltage 406 reaching the target voltage,
S&H circuit 212 stores the output current 404 flowing through
the first number of LED chains of the plurality of LED chains 106.
Since the second number of active LED chains has an operating
voltage that is less than the threshold voltage (V.sub.TH) of the
first number of active LED chains, at time t1, there is no residual
current flowing through the LED chains.
[0052] At time t2, microcontroller 108 activates one or more bypass
switches 110 to selectively activate the second number of LED
chains of the plurality of LED chains 106. The switch from the
first number of LED chains to the second number of LED chains one
or more bypass switches 110 is depicted as line 410. After
activating the second number of LED chains, changed load detector
112 waits until the output current flowing through the second
number of LED chains is higher than the sampled current by a factor
1/(3. Upon determining that the output current is higher than the
sampled current, the driver circuit 100 automatically deactivates,
via a switch, voltage regulation control loop 104 and reactivates
current regulation control loop 102. The connection status of the
current regulation control loop is depicted as line 408.
[0053] S&H circuit 212 of changed load detector 112 is included
to ensure the detection of a change in the plurality of LED chains
106. For example, if a fixed threshold is used, if the threshold is
too high, changed load detector 112 may not detect a small load
change. Similarly, if the fixed threshold is too low, changed load
detector 112 may reactivate the current regulation control loop 102
too soon, which may cause the plurality of LED chains 106 to suffer
an overcurrent condition.
[0054] As seen in FIG. 4A, the driver circuit 100 of the present
disclosure may regulate a constant voltage across the plurality of
LED chains 106 while the number of active LEDs of plurality of LED
chains 106 changes. Therefore, driver circuit 100 may more closely
synchronize the delivery of power to plurality of LED chains 106
while dynamically enabling and disabling one or more of LED chains
106. In contrast to other systems that do not implement the
techniques of the disclosure, such a driver circuit 100 may avoid
inducing ripples, distortions, and overcurrent in the plurality of
LED chains 106, and therefore prevent damage to or decreasing the
operating life of the plurality of LED chains 106. Furthermore, the
driver circuit 100 does not require microcontroller 108 to
continuously poll the output current of the plurality of LED chains
106 to detect a change in the output current or in the number of
active LED chains 106. Thus, such a driver circuit as described
herein may use less power and provide greater precision than other
driver circuits.
[0055] FIG. 4B is a chart illustrating example signals of the
driver circuit 100 of FIG. 1, in accordance with the techniques of
the disclosure. In the example of FIG. 4B, driver circuit 100
drives a first number of active LED chains of the plurality of LED
chains 106. Subsequently, microcontroller 108 selectively activates
a second number of LED chains of the plurality of LED chains 106.
In this example, the second number of active LED chains has an
operating voltage that is greater than the threshold voltage
(V.sub.TH) of the first number of active LED chains. By using the
techniques of the present disclosure, driver circuit 100 may
prevent overcurrent induced in the second number of active LED
chains, thus preventing damage or degradation in the second number
of active LED chains.
[0056] As depicted in FIG. 4B, at time t0 microcontroller
disconnects, via a switch, current regulation control loop 102 and
connects voltage regulation control loop 104. The connection status
of current regulation control loop 102 is depicted as line 408. At
this time, the output current 402 of current regulation control
loop 102 and the output current 414 flowing through the first
number of LED chains of the plurality of LED chains 106 falls (but
does not reach zero). Because voltage regulation control loop 104
is driving the forward voltage 406 of the first number of LED
chains of the plurality of LED chains 106 to the lower target
forward voltage for the second number of LED chains, the forward
voltage 406 similarly falls.
[0057] At time t1, the forward voltage 406 falls to the target
voltage. Upon the forward voltage 406 reaching the target voltage,
S&H circuit 112 stores the output current 414 flowing through
the first number of LED chains of the plurality of LED chains 106.
Since the second number of active LED chains has an operating
voltage that is greater than the threshold voltage (V.sub.TH) of
the first number of active LED chains, at time t1 there is still
residual current flowing on the LED chains.
[0058] At time t2, microcontroller 108 activates one or more bypass
switches 110 to selectively activate the second number of LED
chains of the plurality of LED chains 106. The switch from the
first number of LED chains to the second number of LED chains one
or more bypass switches 110 is depicted as line 410. After
activating the second number of LED chains, changed load detector
112 waits until the output current flowing through the second
number of LED chains is higher than the sampled current by a factor
1/(3. Upon determining that the output current flowing through the
second number of LED chains is higher than the sampled current, the
driver circuit 100 automatically deactivates, via a switch, voltage
regulation control loop 104 and reactivates current regulation
control loop 102. The connection status of the current regulation
control loop is depicted as line 408.
[0059] As seen in FIG. 4B, the driver circuit 100 of the present
disclosure may regulate a constant voltage across the plurality of
LED chains 106 while the number of active LEDs of plurality of LED
chains 106 changes. Therefore, driver circuit 100 may more closely
synchronize the delivery of power to plurality of LED chains 106
while dynamically enabling and disabling one or more of LED chains
106. In contrast to other systems that do not implement the
techniques of the disclosure, such a driver circuit 100 may avoid
inducing ripples, distortions, and overcurrent in the plurality of
LED chains 106, and therefore prevent damage to or decreasing the
operating life of the plurality of LED chains 106. Furthermore, the
driver circuit 100 does not require microcontroller 108 to
continuously poll the output current of the plurality of LED chains
106 to detect a change in the output current or in the number of
active LED chains 106. Thus, such a driver circuit as described
herein may use less power and provide greater precision than other
driver circuits.
[0060] FIG. 5 is a circuit diagram illustrating an example driver
circuit 500 for a plurality of LED chains in accordance with the
techniques of the disclosure. In general, driver circuit 500 of
FIG. 5 functions in a substantially similar fashion to that of
driver circuit 100 of FIG. 1, but is illustrated in further detail.
For example, driver circuit 500 of FIG. 5 includes a current
regulation control loop 102 for regulating a current flowing
through a plurality of LED chains 106, and a voltage regulation
control loop 104 for regulating a voltage across the plurality of
LED chains 106. Driver circuit 500 further includes a plurality of
bypass switches 110 for selectively bypassing one or more LED
chains of the plurality of LED chains 106. Driver circuit 500
includes an S&H circuit 112 that functions to sample an output
current of the plurality of LED chains 106 for comparison to a
current of the changed LED chain by comparator 202.
[0061] In an operation to bypass one or more LED chains of
plurality of LED chains 106, driver circuit 500 deactivates current
regulation control loop 102 and activates voltage regulation
control loop 104. Driver circuit 500 waits until the forward
voltage across the plurality of LED chains 106 falls to a desired
voltage value (e.g., the target operating voltage for a set of
active LED chains of plurality of LED chains 106 that subsequently
are to be enabled). Upon reaching the desired voltage value, driver
circuit 500 activates the S&H circuit which stores the output
current flowing through the plurality of LED chains 106. Further,
driver circuit 500 activates at least one bypass switch of
plurality of bypass switches 110 to bypass the one or more LED
chains of plurality of LED chains 106.
[0062] A comparator 202 compares the output of S&H circuit 112
to a partition of the voltage at the output of a current sense
amplifier. The partition is established by a ratio of resistor
dividers 306. Upon detecting that the current flowing through the
remaining one or more LED chains of plurality of LED chains 106 is
higher than the current stored by changed load detector 112 by a
factor 1/.beta., comparator 202 generates an output indicating
such. In response to the output of comparator 202, driver circuit
500 deactivates voltage regulation control loop 104 and reactivates
current regulation control loop 102.
[0063] Accordingly, the driver circuit 500 of FIG. 5 may regulate a
constant voltage across the plurality of LED chains 106 while the
number of active LEDs of plurality of LED chains 106 changes.
Therefore, driver circuit 500 may more closely synchronize the
delivery of power to plurality of LED chains 106 while dynamically
enabling and disabling one or more of LED chains 106. In contrast
to other systems that do not implement the techniques of the
disclosure, such a driver circuit 500 may avoid inducing
overcurrent plurality of LED chains 106, and prevent damage to or
decreasing the operating life of plurality of LED chains 106.
Furthermore, the driver circuit 500 of FIG. 5 does not require a
microcontroller to continuously poll the output current of the
plurality of LED chains 106 to detect a change in the output
current or in the number of active LED chains 106. Thus, such a
driver circuit as described herein may be cheaper, use less power,
and provide greater precision than other driver circuits.
[0064] FIG. 6 is a circuit diagram illustrating an example control
loop 600 for the driver circuit of FIG. 5, in accordance with the
techniques of the disclosure. In general, the current regulation
control loop 102 and the voltage regulation control loop 104 of
control loop 600 function in a substantially similar fashion to the
like elements of FIG. 5. However, control loop 600 further includes
additional circuitry to provide additional robustness to driver
circuit 500 to correctly detect a change in plurality of LED chains
106, even when the sampled current would be too high for changed
load detector 112 of FIG. 3 to function correctly. In the example
control loop 600 of FIG. 6, current regulation control loop 102
further includes a reference changer 602. Reference changer 602 may
dynamically adjust the ratio of reference resistors 603 so that the
current regulation control loop 102 may still function, but at a
lower reference point. For example, in response to a
microcontroller trigger, control loop 600 selects a lower reference
via resistors 603 for the current regulation control loop 102 and
enables a voltage regulation control loop 104 such that the driver
circuit 500 selects the minimum of two regulation loops (e.g., one
of current regulation control loop 102 and voltage regulation
control loop 104). Thus, output current is always lower or equal to
the lowered reference before driver circuit 500 activates S&H
circuit 212, which stores the output current flowing through the
plurality of LED chains 106. Upon switching the selected number of
the plurality of LED chains 106, driver circuit 500 restores the
reference changer circuit 602 to its original setting, restoring
function to current regulation control loop 102.
[0065] As one example of the above, in response to a
microcontroller trigger, control loop 600 dynamically adjusts, via
reference changer 602, a ratio of reference resistors 603 such that
current regulation control loop 102 operates at a lower reference
point. Further, control loop 600 senses a first output current of
current regulation control loop 102 and a second output current of
voltage regulation control loop 104. Driver circuit 500 determines
a minimum of the first output current and the second output
current, e.g., determines the lesser of the first output current of
current regulation control loop 102 and the second output current
of voltage regulation control loop 104. Based on the determination
of the lesser of the first output current of current regulation
control loop 102 and the second output current of voltage
regulation control loop 104, driver circuit 500 selects one of
current regulation control loop 102 and voltage regulation control
loop 104 to regulate the forward voltage of the plurality of LED
chains 106. For example, if the first output current of current
regulation control loop 102 is less than the second output current
of voltage regulation control loop 104, driver circuit 500
regulates the forward voltage of the plurality of LED chains 106
via current regulation control loop 102. In contrast, if the first
output current of current regulation control loop 102 is greater
than the second output current of voltage regulation control loop
104, driver circuit 500 regulates the forward voltage of the
plurality of LED chains 106 via voltage regulation control loop
104.
[0066] Accordingly, the control loop 600 of FIG. 6 may allow driver
circuit 500 to select one of a current regulation control loop 102
and a voltage regulation control loop 104 when switching the
selected number of the plurality of LED chains 106 such that the
plurality of LED chains do not suffer overcurrent. Such a control
loop may allow driver circuit 500 to correctly detect a change in
the output current of plurality of LED chains 106, even when the
magnitude of the sampled output current would otherwise be too high
for changed load detector 112 to function correctly. Therefore,
driver circuit 500 may more closely synchronize the delivery of
power to plurality of LED chains 106 while dynamically enabling and
disabling one or more of LED chains 106. In contrast to other
systems that do not implement the techniques of the disclosure,
such a driver circuit 500 may avoid inducing overcurrent plurality
of LED chains 106, and prevent damage to or decreasing the
operating life of plurality of LED chains 106. Furthermore, the
control loop 500 does not require a microcontroller to continuously
poll the output current of the plurality of LED chains 106 to
detect a change in the output current or in the number of active
LED chains 106. Thus, such a driver circuit as described herein may
use less power, be cheaper, and provide greater precision than
other driver circuits.
[0067] FIG. 7 is a flowchart illustrating an example operation of
the driver circuit for the plurality of LED chains of FIG. 1, in
accordance with the techniques of the disclosure. For convenience,
FIG. 7 is described with respect to FIG. 1.
[0068] In the example of FIG. 7, driver circuit 100 drives a first
number of active LED chains of the plurality of LED chains 106. In
an operation to activate a second number of LED chains of the
plurality of LED chains 106 (e.g., to bypass one or more LED chains
of plurality of LED chains 106), microcontroller 108 disconnects
the current regulation control loop 102 (700). Further,
microcontroller 108 activates voltage regulation control loop 104
to regulate the forward voltage across the first number of LED
chains of the plurality of LED chains 106 to the target operating
voltage of the second number of LED chains (702).
[0069] Voltage regulation control loop 104 determines whether the
forward voltage across the plurality of LED chains 106 is equal to
a target operating voltage for the second number of LED chains of
the plurality of LED chains 106 to be activated (704). If the
forward voltage across the plurality of LED chains 106 has not
fallen to the target operating voltage (e.g., "NO" block of 704),
voltage regulation control loop 104 continues to wait. If the
forward voltage across the plurality of LED chains 106 has reached
the target operating voltage (e.g., "YES" block of 704), voltage
regulation control loop 104 activates changed load detector 112 to
store the output current flowing through the first number of LED
chains. Further, microcontroller 108 activates at least one bypass
switch of plurality of bypass switches 110 to bypass one or more
LED chains of the plurality of LED chains 106 (706).
[0070] Changed load detector 112 monitors the output current of the
remaining one or more LED chains of the plurality of LED chains 106
to determine when the output current is higher than the stored
value of the changed load detector 112 (708). If this output
current flowing through the plurality of LED chains 106 has not
risen to the target output current (e.g., "NO" block of 708),
changed load detector 112 continues to wait. Upon determining that
the output current for the remaining one or more LED chains of
plurality of LED chains 106 is higher than the stored value of the
changed load detector 112 by a factor 1/0 (e.g., "YES" block of
708), changed load detector 112 deactivates voltage regulation
control loop 104 (710) and reactivates current regulation control
loop 102 (712).
[0071] Accordingly, the driver circuit 100 as described herein may
regulate a constant voltage across the plurality of LED chains 106
prior to changing the number of active LEDs of plurality of LED
chains 106. Therefore, driver circuit 100 may more closely
synchronize the delivery of power to plurality of LED chains 106
while dynamically enabling and disabling one or more of LED chains
106. In contrast to other systems that do not implement the
techniques of the disclosure, such a driver circuit 100 may avoid
inducing overcurrent plurality of LED chains 106, and prevent
damage to or decreasing the operating life of plurality of LED
chains 106. Furthermore, the changed load detector 112 does not
require microcontroller 108 to continuously poll the output current
of the plurality of LED chains 106 to detect a change in the output
current or in the number of active LED chains 106. Thus, such a
driver circuit as described herein may use less power and provide
greater precision than other driver circuits.
[0072] The techniques described in this disclosure may be
implemented, at least in part, in hardware, software, firmware or
any combination thereof. For example, various aspects of the
described techniques may be implemented within one or more
processors, including one or more microprocessors, digital signal
processors (DSPs), application specific integrated circuits
(ASICs), field programmable gate arrays (FPGAs), or any other
equivalent integrated or discrete logic circuitry, as well as any
combinations of such components. The term "processor" or
"processing circuitry" may generally refer to any of the foregoing
logic circuitry, alone or in combination with other logic
circuitry, or any other equivalent circuitry. A control unit
comprising hardware may also perform one or more of the techniques
of this disclosure.
[0073] Such hardware, software, and firmware may be implemented
within the same device or within separate devices to support the
various operations and functions described in this disclosure. In
addition, any of the described units, modules or components may be
implemented together or separately as discrete but interoperable
logic devices. Depiction of different features as modules or units
is intended to highlight different functional aspects and does not
necessarily imply that such modules or units must be realized by
separate hardware or software components. Rather, functionality
associated with one or more modules or units may be performed by
separate hardware or software components, or integrated within
common or separate hardware or software components.
[0074] The techniques described in this disclosure may also be
embodied or encoded in a computer-readable medium, such as a
computer-readable storage medium, containing instructions.
Instructions embedded or encoded in a computer-readable storage
medium may cause a programmable processor, or other processor, to
perform the method, e.g., when the instructions are executed.
Computer readable storage media may include random access memory
(RAM), read only memory (ROM), programmable read only memory
(PROM), erasable programmable read only memory (EPROM),
electronically erasable programmable read only memory (EEPROM),
flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette,
magnetic media, optical media, or other computer readable
media.
[0075] The following examples may illustrate one or more aspects of
the disclosure.
EXAMPLE 1
[0076] A method comprising: deactivating a current regulation
control loop, wherein the current regulation control loop is
connected to a plurality of light-emitting diode (LED) chains in
series; regulating, via a voltage regulation control loop connected
to the plurality of LED chains, a forward voltage of the plurality
of LED chains; upon determining that a forward voltage of the
plurality of LED chains is equal to a target operating voltage for
a subset of the plurality of LED chains, bypassing at least one of
the plurality of LED chains such that only the subset of the
plurality of LED chains is connected to the current regulation
control loop and the voltage regulation control loop; and upon
determining that an output current of the subset of the plurality
of LED chains is equal to a target operating current for the subset
of the plurality of LED chains: deactivating the voltage regulation
control loop; and activating the current regulation control
loop.
EXAMPLE 2
[0077] The method of example 1, wherein determining that the output
current of the subset of the plurality of LED chains is equal to
the target operating current comprises: sensing, via a
microcontroller, the output current of the subset of the plurality
of LED chains; and determining, via the microcontroller, that the
output current is equal to the target operating current.
EXAMPLE 3
[0078] The method of example 1, wherein determining that the output
current of the subset of the plurality of LED chains is equal to
the target operating current comprises: sensing, via a changed load
detector circuit, an output current of the plurality of LED chains;
storing, via a sample and hold circuit of the changed load detector
circuit, a value of the sensed output current of the plurality of
LED chains; and comparing, via a comparator of the changed load
detector circuit, the stored value to an output current of the
subset of the plurality of LED chains.
EXAMPLE 4
[0079] The method of any of examples 1-3, wherein regulating the
forward voltage of the plurality of LED chains comprises:
dynamically adjusting a ratio of reference resistors such that the
current regulation control loop operates at a lower reference
point; sensing a first output current of the current regulation
control loop; sensing a second output current of the voltage
regulation control loop; determining a minimum of the first output
current and the second output current; and regulating the forward
voltage of the plurality of LED chains via one of the current
regulation control loop and the voltage regulation control loop
based on the determined minimum of the first output current and the
second output current.
EXAMPLE 5
[0080] The method of any of examples 1-4, wherein one of a DC-DC
current regulator or a linear current regulator comprises the
current regulation control loop.
EXAMPLE 6
[0081] The method of any of examples 1-5, wherein the plurality of
LED chains provides a plurality of different functions for a
vehicle illumination system.
EXAMPLE7
[0082] The method of example 6, wherein: a first LED chain of the
plurality of LED chains provides high-beam headlight functionality
for the vehicle illumination system; a second LED chain of the
plurality of LED chains provides low-beam headlight functionality
for the vehicle illumination system; a third LED chain of the
plurality of LED chains provides corner light functionality for the
vehicle illumination system; a fourth LED vehicle illumination
system of the plurality of LED chains provides daytime running
light functionality for the vehicle; and a fifth LED chain of the
plurality of LED chains provides positioning light functionality
for the vehicle illumination system.
EXAMPLE 8
[0083] A driver circuit for a plurality of light-emitting diode
(LED) chains, configured to: deactivate a current regulation
control loop, wherein the current regulation control loop is
connected to a plurality of light-emitting diode (LED) chains;
regulate, via a voltage regulation control loop connected to the
plurality of LED chains, a forward voltage of the plurality of LED
chains; upon determining that a forward voltage of the plurality of
LED chains is equal to a target operating voltage for a subset of
the plurality of LED chains, bypass at least one of the plurality
of LED chains such that only the subset of the plurality of LED
chains is connected to the current regulation control loop and the
voltage regulation control loop; and upon determining that an
output current of the subset of the plurality of LED chains is
equal to a target operating current for the subset of the plurality
of LED chains: deactivate the voltage regulation control loop; and
activate the current regulation control loop.
EXAMPLE 9
[0084] The driver circuit of example 8, wherein the driver circuit
comprises a microcontroller configured to: sense the output current
of the subset of the plurality of LED chains; and determine that
the output current is equal to the target operating current.
EXAMPLE 10
[0085] The driver circuit of example 8, wherein the driver circuit
further comprises: a changed load detector circuit configured to
sense an output current of the plurality of LED chains; a sample
and hold circuit of the changed load detector circuit configured to
store a value of the sensed output current of the plurality of LED
chains; and a comparator of the changed load detector circuit
configured to compare the stored value to an output current of the
subset of the plurality of LED chains.
EXAMPLE 11
[0086] The driver circuit of any of examples 8-10, wherein the
driver circuit is further configured to: dynamically adjust a ratio
of reference resistors such that the current regulation control
loop operates at a lower reference point; sense a first output
current of the current regulation control loop; sense a second
output current of the voltage regulation control loop; determine a
minimum of the first output current and the second output current;
and regulate the forward voltage of the plurality of LED chains via
one of the current regulation control loop and the voltage
regulation control loop based on the determined minimum of the
first output current and the second output current.
EXAMPLE 12
[0087] The driver circuit of any of examples 8-11, wherein one of a
DC-DC current regulator or a linear current regulator comprises the
current regulation control loop.
EXAMPLE 13
[0088] The driver circuit of any of examples 8-12, wherein the
plurality of LED chains provides a plurality of different functions
for a vehicle illumination system.
EXAMPLE 14
[0089] A system comprising: a driver circuit, configured to:
deactivate a current regulation control loop, wherein the current
regulation control loop is connected to a plurality of
light-emitting diode (LED) chains; regulate, via a voltage
regulation control loop connected to the plurality of LED chains, a
forward voltage of the plurality of LED chains; upon determining
that a forward voltage of the plurality of LED chains is equal to a
target operating voltage for a subset of the plurality of LED
chains, bypass at least one of the plurality of LED chains such
that only the subset of the plurality of LED chains is connected to
the current regulation control loop and the voltage regulation
control loop; and upon determining that an output current of the
subset of the plurality of LED chains is equal to a target
operating current for the subset of the plurality of LED chains:
deactivate the voltage regulation control loop; and activate the
current regulation control loop; and the plurality of LED
chains.
EXAMPLE 15
[0090] The system of example 14, wherein the driver circuit
comprises a microcontroller configured to: sense the output current
of the subset of the plurality of LED chains; and determine that
the output current is equal to the target operating current.
EXAMPLE 16
[0091] The system of example 14, wherein the driver circuit further
comprises: a changed load detector circuit configured to sense an
output current of the plurality of LED chains; a sample and hold
circuit of the changed load detector circuit configured to store a
value of the sensed output current of the plurality of LED chains;
and a comparator of the changed load detector circuit configured to
compare the stored value to an output current of the subset of the
plurality of LED chains.
EXAMPLE 17
[0092] The system of examples 14-16, wherein the driver circuit is
further configured to: dynamically adjust a ratio of reference
resistors such that the current regulation control loop operates at
a lower reference point; sense a first output current of the
current regulation control loop; sense a second output current of
the voltage regulation control loop; determine a minimum of the
first output current and the second output current; and regulate
the forward voltage of the plurality of LED chains via one of the
current regulation control loop and the voltage regulation control
loop based on the determined minimum of the first output current
and the second output current.
EXAMPLE 18
[0093] The system of any of examples 14-17, wherein one of a DC-DC
current regulator or a linear current regulator comprises the
current regulation control loop.
EXAMPLE 19
[0094] The system of any of examples 14-18, wherein the plurality
of LED chains provides a plurality of different functions for a
vehicle illumination system.
EXAMPLE 20
[0095] The driver circuit of example 19, wherein: a first LED chain
of the plurality of LED chains provides high-beam headlight
functionality for the vehicle illumination system; a second LED
chain of the plurality of LED chains provides low-beam headlight
functionality for the vehicle illumination system; a third LED
chain of the plurality of LED chains provides corner light
functionality for the vehicle illumination system; a fourth LED
vehicle illumination system of the plurality of LED chains provides
daytime running light functionality for the vehicle; and a fifth
LED chain of the plurality of LED chains provides positioning light
functionality for the vehicle illumination system.
[0096] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *