U.S. patent application number 14/958737 was filed with the patent office on 2017-06-08 for buck converter electronic driver with enhanced ithd.
The applicant listed for this patent is Infineon Technologies Austria AG. Invention is credited to Xiaowu Gong, Yong Siang Teo.
Application Number | 20170163151 14/958737 |
Document ID | / |
Family ID | 58722905 |
Filed Date | 2017-06-08 |
United States Patent
Application |
20170163151 |
Kind Code |
A1 |
Teo; Yong Siang ; et
al. |
June 8, 2017 |
BUCK CONVERTER ELECTRONIC DRIVER WITH ENHANCED ITHD
Abstract
Methods, devices, techniques, systems, and integrated circuits
are disclosed for variably controlling a switch on time for a
driver, which may enhance iTHD. In one example, a device includes
an input voltage sensor configured to detect an input voltage, and
a variable switch on time generator, operatively connected to the
input voltage sensor to receive a signal indicative of the input
voltage. The variable switch on time generator is configured to
determine a variable switch on time based at least in part on the
detected input voltage, and output the determined variable switch
on time for controlling switch on timing of a driver switch.
Inventors: |
Teo; Yong Siang; (Singapore,
SG) ; Gong; Xiaowu; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies Austria AG |
Villach |
|
AT |
|
|
Family ID: |
58722905 |
Appl. No.: |
14/958737 |
Filed: |
December 3, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/37 20200101;
Y02B 20/30 20130101; H02M 2001/4291 20130101; H02M 1/4208 20130101;
Y02B 70/126 20130101; Y02B 20/346 20130101; Y02B 70/10
20130101 |
International
Class: |
H02M 3/158 20060101
H02M003/158; H05B 33/08 20060101 H05B033/08 |
Claims
1. A device comprising: an input voltage sensor configured to
detect an input voltage; and a variable on time generator
comprising an on time measurement capacitor, a controller input
pin, and a voltage comparison pin, wherein the variable on time
generator is operatively connected to the input voltage sensor via
the controller input pin to receive a signal indicative of the
input voltage, and the variable on time generator is configured to:
determine a variable switch on time based at least in part on the
detected input voltage, wherein determining the variable switch on
time comprises charging the on time measurement capacitor via the
voltage comparison pin until the on time measurement capacitor
reaches a voltage level of the controller input pin; and generate
an output based on the determined variable switch on time for
controlling switch on timing of a driver switch.
2. The device of claim 1, wherein the variable switch on time
generator is further configured to determine the variable switch on
time to be proportional to the input voltage for at least a portion
of an alternating current (AC) cycle of the input voltage.
3. The device of claim 1, wherein the input voltage sensor and the
variable switch on time generator are further configured to
determine the variable switch on time to be proportional to the
input voltage at times that the input voltage is above a threshold
minimum voltage, and to determine the variable switch on time to be
constant at a threshold minimum switch on time at times that the
input voltage is below the threshold minimum voltage.
4. The device of claim 1, wherein the input voltage sensor
comprises a minimum voltage clamp coupled to a power input, wherein
the minimum voltage clamp configures the input voltage sensor to
output a signal indicative of a minimum threshold voltage to the
variable switch on time generator in response to the input voltage
falling below the minimum threshold voltage.
5. The device of claim 4, wherein the minimum voltage clamp
comprises an input pin coupled to a high voltage side of the power
input, and an alternative input pin coupled at least in part to a
low voltage side of the power input.
6. The device of claim 5, wherein the alternative input pin is
coupled via the low voltage side of the power input to a capacitor
that is coupled on its opposing side to the high voltage side of
the power input.
7. (canceled)
8. A method comprising: detecting an input voltage; determining a
variable switch on time based at least in part on the detected
input voltage, wherein determining the variable switch on time
based at least in part on the detected input voltage further
comprises charging an on time measurement capacitor via a voltage
comparison pin until the on time measurement capacitor reaches the
detected input voltage; and generating an output based on the
determined switch on time for controlling switch on timing of a
driver switch.
9. The method of claim 8, further comprising determining the
variable switch on time to be proportional to the input voltage for
at least a portion of an alternating current (AC) cycle of the
input voltage.
10. The method of claim 8, wherein determining the variable switch
on time further comprises: determining the variable switch on time
to be proportional to the input voltage at times that the input
voltage is above a threshold minimum voltage; and determining the
variable switch on time to be constant at a threshold minimum
switch on time at times that the input voltage is below the
threshold minimum voltage.
11. The method of claim 8, further comprising: clamping a minimum
threshold voltage in response to the input voltage falling below
the minimum threshold voltage; and determining the variable switch
on time based on the minimum threshold voltage.
12. The method of claim 11, wherein clamping the minimum threshold
voltage comprises receiving a voltage from a high voltage side of a
power input, and receiving an alternative voltage at least in part
from a low voltage side of the power input.
13. The method of claim 12, wherein receiving an alternative
voltage further comprises receiving a voltage from a capacitor that
is coupled on an opposing side of the capacitor to the high voltage
side of the power input.
14. (canceled)
15. A system comprising: an on time measurement capacitor; a
controller input pin; and a voltage comparison pin, wherein the
system is configured to: detect an input voltage; determine a
variable switch on time based at least in part on the detected
input voltage, wherein determining the variable switch on time
based at least in part on the detected input voltage comprises
charging the on time measurement capacitor via the voltage
comparison pin until the on time measurement capacitor reaches a
voltage level of the controller input pin; and generate an output
based on the determined switch on time for controlling switch on
timing of a driver switch.
16. The system of claim 15, comprising an input voltage sensor
configured to detect the input voltage.
17. The system of claim 15, comprising a variable switch on time
generator, operatively connected to the input voltage sensor to
receive a signal indicative of the input voltage, the variable
switch on time generator configured to determine the variable
switch on time based at least in part on the detected input
voltage, and output the determined switch on time for controlling
switch on timing of a driver switch.
18. The system of claim 15, wherein the system is further
configured to determine the variable switch on time to be
proportional to the input voltage for at least a portion of an
alternating current (AC) cycle of the input voltage.
19. The system of claim 15, wherein the system is further
configured such that determining the variable switch on time
further comprises: determining the variable switch on time to be
proportional to the input voltage at times that the input voltage
is above a threshold minimum voltage; and determining the variable
switch on time to be constant at a threshold minimum switch on time
at times that the input voltage is below the threshold minimum
voltage.
20. (canceled)
Description
TECHNICAL FIELD
[0001] This disclosure relates to electronic drivers, and in
particular, to electronic drivers with DC-DC buck converters.
BACKGROUND
[0002] Electrical power converters are used to meet specialized
current and voltage requirements of a load with the available
source power. Buck converters are popular for use in electronic
drivers in a variety of applications, such as light-emitting diode
(LED) lighting. For example, chains of LEDs may require a certain
DC voltage and current for proper operation. LED chains may
typically be powered with two-stage control gear including an AC-DC
voltage converter and a DC-DC current converter, typically a
step-down or buck converter with a lower output voltage than input
voltage. Buck converters typically offer advantages such as low
component count, low cost, and high efficiency.
SUMMARY
[0003] In general, various examples of this disclosure are directed
to techniques and methods for a buck converter with enhanced total
harmonic distortion in current (iTHD) for electronic drivers.
Despite certain advantages, typical buck drivers have poor iTHD
(e.g., .about.13%-26%) when operating with low output voltage and
high AC mains power, due to filter-induced phase latency between
the driver input current and input voltage. Various examples of
this disclosure may combine the traditional advantages of buck
drivers with enhanced iTHD as well. Some traditional driver designs
have sought to address THD with an enhanced electromagnetic
interference (EMI) filter or an enhanced capacitor-input (pi)
filter. However, these solutions tend to be bulky, impact power
factor and output current ripple, and only have limited success in
managing THD.
[0004] Instead, various examples of this disclosure may enhance
iTHD by incorporating an input voltage sensor and a variable switch
on time generator that may vary a switch on time based on the input
voltage detected by the input voltage sensor. The input voltage
sensor and the variable switch on time generator may thereby
implement a current waveform shaping function on the current
received at the input prior to supplying the current to a load. The
input current waveform shaping function of this disclosure may
involve varying the power switching time relative to the input
voltage, as further described below. Examples of this disclosure
may improve iTHD in a way that may also enhance power factor (PF).
Examples of this disclosure may thus combine advantages of a buck
converter with enhanced iTHD while avoiding the drawbacks of
relying on an enhanced EMI filter or enhanced pi filter.
[0005] One example is directed to a device that includes an input
voltage sensor configured to detect an input voltage, and a
variable switch on time generator, operatively connected to the
input voltage sensor to receive a signal indicative of the input
voltage. The variable switch on time generator is configured to:
determine a variable switch on time based at least in part on the
detected input voltage; and output the determined variable switch
on time for controlling switch on timing of a driver switch.
[0006] Another example is directed to a method including detecting
an input voltage; determining a variable switch on time based at
least in part on the detected input voltage; and outputting the
determined switch on time for controlling switch on timing of a
driver switch.
[0007] Another example is directed to system configured to detect
an input voltage; determine a variable switch on time based at
least in part on the detected input voltage; and output the
determined switch on time for controlling switch on timing of a
driver switch.
[0008] The details of one or more examples of this disclosure are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages will be apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a conceptual block diagram of an electronic driver
with a driver controller that includes an input voltage responsive
variable switch on time generator ("variable on time generator"),
and an input voltage sensor operatively connected to variable on
time generator to signal a detected input voltage to variable on
time generator, in one aspect of this disclosure.
[0010] FIG. 2 is a more detailed conceptual block diagram of an
electronic driver with a variable on time generator and an input
voltage sensor, in one aspect of this disclosure.
[0011] FIG. 3 shows a graph of input voltage and switch on time
over time during one AC half-cycle of an AC power input, where the
switch on time is controlled by a variable on time generator based
at least in part on the input voltage, in one aspect of this
disclosure.
[0012] FIG. 4 shows a graph comparing a driver current over time of
a traditional buck converter driver, and a driver current over time
resulting from the operation of a variable on time generator of
this disclosure, for one full AC input cycle, in one aspect of this
disclosure.
[0013] FIG. 5 is a flowchart illustrating a method of operating an
input voltage sensor and a variable on time generator of this
disclosure in a way that may better synchronize output current with
input voltage, reduce higher-order current harmonics, and reduce
iTHD, among other advantages, in one aspect of this disclosure.
DETAILED DESCRIPTION
[0014] FIG. 1 is a conceptual block diagram of an electronic driver
100 with a driver controller 110 that includes an input voltage
responsive variable switch on time (T.sub.ON) generator 120
("variable on time generator 120"), and an input voltage sensor 130
operatively connected to variable on time generator 120 to signal a
detected input voltage to variable on time generator 120, in one
aspect of this disclosure. Electronic driver also includes 100 AC
power input terminal 102 and a filtering and conditioning block 104
connected to drive filtered and conditioned electrical power to a
load 150, such as a chain of LEDs. Filtering and conditioning block
104 may include, for example, an EMI filter, a pi filter, an input
smoothing capacitor, and/or an AC-DC current rectifier. Driver 100
may thus deliver a smoothed DC current to load 150.
[0015] Variable on time generator 120 is connected to input voltage
sensor 130 in a configuration such that variable on time generator
120 may receive an input from input voltage sensor 130 indicative
of an input voltage at AC power input terminal 102, and may control
the switch on timing of switch 126 of driver 100 with variable on
times based on the input voltage. Switch 126 may be a metal-oxide
semiconductor field effect transistor (MOSFET) or other
semiconductor switch configured to control switching a current on
and off in response to a switch on signal, in various examples.
[0016] Variable on time generator 120 may apply a higher switch on
time, or T.sub.ON time, when the sensed input voltage is high,
leading to a higher current draw by load 150 from AC power input
102 during a high-voltage portion of the AC cycle of the input
voltage. Conversely, variable on time generator 120 may apply a
lower switch on time when the sensed input voltage is low, leading
to a lower current draw by load 150 from AC power input 102 during
a low-voltage portion of the AC cycle of the input voltage. By
doing so, variable on time generator 120 may shape the current
waveform from its initial shape as received via AC power input 102,
and reduce one or more higher-order harmonics in the current, thus
reducing and enhancing the iTHD, prior to supplying the current to
load 150. Variable on time generator 120 may also limit the lower
variations in switch on time to a minimum switch on time, to ensure
sufficient current for proper operation of load 150, such as to
avoid human-perceptible flicker in an LED lighting application, for
example.
[0017] For example, variable on time generator 120 may be
configured to determine a variable switch on time to be
proportional to the input voltage, and to output a control signal
for a switch on time that is proportional to the input voltage. In
some examples, variable on time generator 120 may also enforce a
threshold minimum switch on time regardless of the input voltage
once the input voltage is below a threshold minimum voltage. In
such examples, variable on time generator 120 may be configured to
determine the variable switch on time to be proportional to the
input voltage when the input voltage is above the threshold minimum
voltage, and to determine the variable switch on time to be
constant at a threshold minimum switch on time when the input
voltage is below the threshold minimum voltage. Aspects of driver
100 with variable on time generator 120 are further described with
reference to various examples below.
[0018] FIG. 2 is a more detailed conceptual block diagram of an
electronic driver 200 with a variable on time generator 220 and an
input voltage sensor 230, in one aspect of this disclosure. Driver
200 of FIG. 2 may be an implementation of electronic driver 100
shown in FIG. 1. In FIG. 2, electronic driver 200 also includes an
AC power input 202, a filtering and conditioning block 204, a
driver controller 210, and a switch 226 that are analogous to their
counterparts described above with reference to FIG. 1. Switch 226
may be a metal-oxide semiconductor field effect transistor (MOSFET)
or other semiconductor switch configured to control switching a
current on and off in response to a switch on signal, in various
examples. Driver 200 drives a load 250, such as a chain of LED
lights, analogously to driver 100 driving load 150 as shown in FIG.
1.
[0019] Analogously to FIG. 1, filtering and conditioning block 204
may include, for example, an EMI filter, a pi filter, an input
smoothing capacitor, and/or an AC-DC current rectifier. Driver 200
may thus deliver a smoothed DC current to load 250, with timing of
the supply of current to load 250 controlled via switch 226. The
timing of switch 226 in turn is controlled by driver controller
210, which includes variable on time generator 220 in operative
communication with input voltage sensor 230. Driver controller 210
may further include additional features and components and
implement additional functions as described below.
[0020] Driver 200 as illustrated in FIG. 2 shows further detail on
how input voltage sensor 230 may detect the input voltage of AC
power input 202 and output a signal indicative of input voltage of
AC power input 202 to variable on time generator 220. Driver 200 as
illustrated in FIG. 2 also shows further detail on how variable on
time generator 220 may receive the signal indicative of the input
voltage of AC power input 202 from input voltage sensor 230, and
how variable on time generator 220 may be configured to determine a
switch on time based at least in part on the input voltage, and
output the determined switch on time to switch 226. Variable on
time generator 220 may cause switch 226 to switch on for longer on
times proportionally to higher input voltages, at least during part
of an AC half-cycle of input voltages. Variable on time generator
220 may thus shape the waveform of the current received via AC
power input 202 before delivering the waveform-shaped current to
load 250 by driver 200, thereby causing an enhanced, lower iTHD and
enhanced power factor, among other advantages.
[0021] Input voltage sensor 230 may be implemented with an input
pin 232, a resistor ladder 234, and a sampling pin 236, in this
example. Input voltage sensor 230 may receive the voltage of AC
power input 202 via input pin 232, pass the input voltage through
resistor ladder 234, and sample a voltage at sampling pin 236.
Resistor ladder 234 may be tuned or adjusted to adjust iTHD
performance of driver 200. Resistor ladder 234 is illustratively
depicted as including two resistors in FIG. 2., one on either side
of sampling pin 232, but may include any number and arrangement of
resistors in other examples. Resistor ladder 234 may be tuned or
adjusted by tuning or adjusting the resistance values, number,
and/or arrangement of its constituent resistors, for example.
[0022] Input voltage sensor 230 may also include minimum voltage
clamp 238 applied to input pin 232. Minimum voltage clamp 238 may
contribute to ensuring a minimum voltage detected and signaled by
input voltage sensor 230, independently of the voltage at AC power
input 202 if the voltage at AC power input 202 falls below a
certain minimum threshold voltage that may be defined or
implemented by minimum voltage clamp 238. In the example depicted
in FIG. 2, minimum voltage clamp 238 is implemented with parallel,
isotropic diodes disposed on input pin 232 and on alternative input
pin 233. Input pin 232 is coupled simply to the high voltage side
203 of AC power input 202, with its diode admitting current from AC
power input 202. Alternative input pin 233 is coupled via its diode
to the low voltage side 205 of AC power input 202, and thereby to a
capacitor that is also coupled on its opposing side to high voltage
side 203 of AC power input 202. Minimum voltage clamp 238 is thus
implemented to draw at least a minimum voltage from AC power input
202, regardless of the voltage at the high side of AC power input
202.
[0023] Minimum voltage clamp 238 thus includes input pin 232
coupled to high voltage side 203 of AC power input 202, and
alternative input pin 233 coupled at least in part to low voltage
side 205 of AC power input 202. Alternative input pin 233 is
coupled at least in part to the low voltage side of AC power input
202 inasmuch as it is also coupled to capacitor 209 which is
coupled on its opposing side to high side 203 of AC power input
202, in the example of FIG. 2. This is one more particular example
of how minimum voltage clamp 238 may be implemented to draw at
least a minimum voltage from AC power input 202, regardless of the
voltage at the high side of AC power input 202. Thus, minimum
voltage clamp 238 of input voltage sensor 230 may clamp a minimum
threshold voltage in alternative to the input voltage, and
determine the variable switch on time based on the minimum
threshold voltage in response to the input voltage falling below
the minimum threshold voltage, in some examples.
[0024] Variable on time generator as implemented in the example of
FIG. 2 includes a voltage clamp 222, an on time measurement
capacitor 224, and a switch (e.g., MOSFET) 228, interconnected as
depicted in FIG. 2. Driver controller 210 further includes
components and features such as controller input pin 242; a drain
pin 244; a supply voltage (V.sub.CC) pin 246; an output (CS) pin
248 coupled to a current sense resistor 249; a voltage comparison
pin 252 coupled to a current comparison capacitor 253; a variable
current selection unit 254; a valley detector 256; a peak detector
258; a voltage comparison amplifier 260; operational amplifiers (op
amps) 262 and 264; a set-reset latch 266 ("latch 266"); and a
switch (e.g., MOSFET) 268, interconnected as depicted in FIG. 2.
Driver controller 210 may thus implement supply of a switch on time
to switch 226 based on the detection of the input voltage and
operation of generating variable switch on time by input voltage
sensor 230 and variable on time generator 220. Various
implementations may also include additional features or components
besides those shown in FIG. 2 and described herein, and/or may omit
one or more of the illustrative features and components of driver
controller 210 as shown in FIG. 2 and described herein.
[0025] As shown in FIG. 2, variable on time generator 220 may
receive a voltage signal indicative of the input voltage from input
voltage sensor 230 via controller input pin 242. Variable on time
generator 220 may use the voltage or voltage signal at controller
input pin 242 as a reference voltage. Voltage clamp 222 of variable
on time generator 220 is coupled to controller input pin 242 and to
one input of op amp 262. The other input of op amp 262 is coupled
to on time measurement capacitor 224 and one input of switch 228 of
variable on time generator 220. The output of op amp 262 is coupled
to a reset pin of latch 266, while valley detector 256 is coupled
to the set pin of latch 266. Valley detector 256 may detect a
minimum output voltage.
[0026] Voltage comparison pin 252 is coupled to voltage comparison
amplifier 260 and to one input of op amp 264. Voltage comparison
amplifier 260 may have a gain of 3.5 as shown in the example of
FIG, 2, and may have a gain of a higher or lower value in other
examples. Peak detector 258 is coupled to voltage comparison
amplifier 260. Peak detector 258 may detect a peak output voltage.
The other input of op amp 264 is coupled to a reference voltage,
which is 1.5 volts as shown in the example of FIG. 2, and may have
a higher or lower value in other embodiments.
[0027] Op amp 264 is coupled to variable current selection unit
254, which in turn is coupled to on time measurement capacitor 224
and switch 228 of variable on time generator 220 and to the
corresponding input of op amp 262. Variable on time generator 220
may thus use a variable current that is dependent on a voltage
level via voltage comparison pin 252 to charge up on time
measurement capacitor 224. When the voltage at the on time
measurement capacitor 224 reaches the voltage level of controller
input pin 242, variable on time controller 220 causes the gate of
switch 228 of variable on time generator 20 to turn off, thereby
controlling the signal timing of controller 210.
[0028] The output of latch 266 is coupled to switch 268 of
controller 210, which in turn is coupled to drain 244 and thereby
to switch 226 of driver 200. The output of latch 266 is also
coupled to switch 228 of variable on time controller 220.
Controller 210 and variable on time generator 220 may thus
implement variable switching times of switch 226 of driver 200
based on the detected input voltage at AC power input 202 as sensed
by input voltage sensor 230, and proportional to the detected input
voltage across at least a portion of the voltage range of the input
voltage. Controller 210, variable on time generator 220, and input
voltage sensor 230 may thus regulate the output current of driver
200, with reference to current comparison capacitor 253, and ensure
that driver 200 supplies load 250 with current proportional to the
input voltage, at least across a portion of the input voltage
range. Controller 210, variable on time generator 220, and input
voltage sensor 230 may also be implemented in a variety of other
ways and with other specific features, components, and
interconnections among them in other examples.
[0029] FIG. 3 shows a graph 300 of input voltage 312 and switch on
time 322 over time during one AC half-cycle of an AC power input
302, where switch on time 322 is controlled by a variable on time
generator 320 based at least in part on the input voltage 312, in
one aspect of this disclosure. Input voltage 312 oscillates from 0
to 330 volts and back again, as shown relative to the upper y axis,
and switch on time 322 is varied under control of variable on time
generator 320 between 320 and 385 microseconds in this example, as
shown relative to the lower y axis, both over an AC half-cycle
duration of 10 milliseconds, as shown relative to the x axis.
[0030] In the example of FIG. 3, variable on time generator 320
enforces a threshold minimum on time of 320 microseconds at times
that input voltage 312 falls below a threshold minimum voltage of
220 volts. The threshold minimum voltage is a threshold minimum as
observed by variable on time generator 320, and not by AC power
input 302, for purposes of enforcing the threshold minimum on time.
When input voltage 312 is above the threshold minimum voltage of
220 volts, variable on time generator 320 controls the switch on
time 322 to vary proportionally with input voltage 312, such that
as input voltage 312 rises and falls, switch on time 322 rises and
falls in proportion with input voltage 312. In this example,
variable on time generator 320 controls switch on time 322 to rise
from the threshold minimum on time of 320 microseconds up to a peak
on time of 385 microseconds, in tandem with input voltage rising
from the threshold minimum voltage of 220 volts to a peak voltage
of 330 volts. Switch on time 322 may also have a brief sigmoidal
transition between the constant portion and the proportional
portion of switch on time 322, and the transition from proportional
portion back to constant portion of switch on time 322. Variable on
time generator 320 may thus advantageously raise the switch on time
322 and the resulting current delivered to a load proportionately
to higher levels of input voltage 312, while still maintaining
sufficient current delivered to the load during times of lower
levels of input voltage 312. Variable on time generator 320 may
thus inhibit one or more higher harmonics in the current and reduce
iTHD.
[0031] In theory, the iTHD is commonly defined as the ratio of the
root mean square (RMS) amplitude of a set of higher harmonic
frequencies to the RMS amplitude of the first harmonic, or
fundamental, frequency. The formula for iTHD is given below:
iTHD = I 2 2 + I 3 2 + I 4 2 + + I N 2 I 1 ( Equation 1 )
##EQU00001##
where I is the RMS current of the Nth harmonic and N=1 is the
fundamental harmonic. In some typical drivers, current passes from
the input through an EMI filter and a pi filter with a bulk
capacitor to the load, which causes the current to be out of phase
with the voltage, and diverts a substantial amount of the energy in
the current into higher order harmonics of the current,
particularly the first one or more harmonics, thereby causing
relatively high iTHD. In contrast, as shown in FIG. 3, variable on
time generator 320 may shape the current waveform delivered to the
load and inhibit one or more higher harmonics in the current and
reduce iTHD, as further demonstrated in FIG. 4.
[0032] FIG. 4 shows a graph 400 comparing a driver output current
412 over time of a traditional buck converter driver, and a driver
output current 422 over time resulting from the operation of a
variable on time generator of this disclosure, for one full AC
input cycle, in one aspect of this disclosure. Graph 400 also shows
an original AC input voltage 402 and a rectified AC input voltage
404 over a corresponding AC input cycle for comparison. Driver
output current 412 of a traditional buck converter driver displays
a substantially uneven shape relative to a sine wave, indicative of
significant current-voltage phase latency, substantial higher-order
current harmonics, and relatively high iTHD.
[0033] On the other hand, driver output current 422 resulting from
the operation of a variable on time generator of this disclosure
(e.g., variable on time generator 120, 220, 320), in cooperation
with direct sensing of the input voltage via an input voltage
sensor of this disclosure (e.g., input voltage sensor 130, 230),
shows substantially closer adherence to an ideal sine wave shape,
indicative of lower current-voltage phase latency, reduced
higher-order current harmonics, and relatively low iTHD. As a
particular example, some implementations of this disclosure may
particularly substantially reduce energy in the third current
harmonic (I.sub.3). Some implementations of this disclosure may
particularly substantially reduce energy in both the third and
fifth current harmonics (I.sub.3 and I.sub.5). Other
implementations may significantly reduce energy across a wide
variety of current harmonics in favor of the fundamental
frequency.
[0034] When the detected input voltage sensed by the input voltage
sensor and communicated to the variable on time generator is
relatively high, the variable on time generator causes the switch
on time to be relatively high, leading to more current drawn from
the AC power input. On the other hand, when the detected input
voltage sensed by the input voltage sensor and communicated to the
variable on time generator is relatively low, the variable on time
generator causes the switch on time to be relatively low, leading
to less current drawn from the AC power input. Driver output
current 422 resulting from the operation of a variable on time
generator of this disclosure may thus shape the waveform of driver
output current 422 and reduce distortion in the output current due
to voltage-current phase lag.
[0035] As in the example of FIG. 3, the variable on time generator
may also enforce a minimum switch on time to ensure that crossover
distortion is not worsened, and that current supplied to the load
does not fall below a minimum threshold. The minimum threshold may
be set or selected based on the operating parameters of the load.
For example, the load may be an LED chain, and the minimum
threshold may be set or selected to ensure that the current
supplied to the LED chain does not fall low enough to cause any
human-perceptible flickering or faltering of the light emitted by
the LED chain.
[0036] FIG. 5 is a flowchart illustrating a method 500 of operating
an input voltage sensor and a variable on time generator of this
disclosure in a way that may better synchronize output current with
input voltage, reduce higher-order current harmonics, and reduce
iTHD, among other advantages, in one aspect of this disclosure.
Method 500 may be a more generalized form of the operation of
various input voltage sensors and/or variable on time generators of
this disclosure, including a generalized form of the operation of
input voltage sensors 130 and 230 and/or variable on time
generators 120, 220, and 320, including in producing switch on time
322 and/or output current 422, as described above with reference to
FIGS. 1-4.
[0037] In the example of FIG. 5, method 500 includes detecting an
input voltage (e.g., input voltage sensors 130 or 230 detecting the
input voltage of AC power input 102 or 202 as described with
reference to FIGS. 1 and 2) (502). Method 500 further includes
determining a variable switch on time based at least in part on the
detected input voltage (e.g., variable on time generators 120, 220,
or 320 determining a variable switch on time based at least in part
on the detected input voltage indicated by input voltage sensors
130 or 230, and potentially also based on a constant threshold
minimum switch on time at times when the input voltage is below a
threshold minimum voltage, as described with reference to FIGS.
1-4) (504). Method 500 further includes outputting the determined
switch on time for controlling switch on timing of a driver switch
(e.g., variable on time generators 120, 220, or 320 outputting a
switch on timing signal for communication to switch 126 or 226,
potentially by way of additional processing functions performed by
other components of a driver controller 110 or 210 as shown
particularly in FIG. 2, resulting in switch on times characterized
by graphs 300 and 400 of FIGS. 3 and 4) (506).
[0038] Any of the circuits, devices, and methods described above
may be embodied in or performed in whole or in part by any of
various types of integrated circuits, chip sets, and/or other
devices, and/or as software executed by a computing device, for
example. This may include processes performed by, executed by, or
embodied in one or more microcontrollers, central processing units
(CPUs), processing cores, field-programmable gate arrays (FPGAs),
programmable logic devices (PLDs), virtual devices executed by one
or more underlying computing devices, or any other configuration of
hardware and/or software.
[0039] For example, a variable on time generator and/or an input
voltage sensor of this disclosure (e.g., variable on time
generators 120, 220, or 320, input voltage sensors 130 or 230) may
be implemented or embodied with one or more integrated circuits
configured, via any combination of hardware, logic, general purpose
processors, application specific integrated circuits (ASICs), field
programmable gate arrays (FPGAs), and/or general processing
circuits, which may execute software instructions in some examples,
to perform various functions described herein. A variable on time
generator and/or an input voltage sensor of this disclosure may
also be configured with various other circuit elements and with
operative connections therebetween. The integrated circuits and
other circuit elements may be configured to perform any of the
functions or processes described above.
[0040] Additional aspects of this disclosure are enumerated as
follows as aspects A1-A20.
[0041] A1. In one aspect A1 of this disclosure, a device includes
an input voltage sensor configured to detect an input voltage; and
a variable switch on time generator, operatively connected to the
input voltage sensor to receive a signal indicative of the input
voltage, the variable switch on time generator configured to:
determine a variable switch on time based at least in part on the
detected input voltage; and output the determined variable switch
on time for controlling switch on timing of a driver switch.
[0042] A2. A device of aspect A1, wherein the variable switch on
time generator is further configured to determine the variable
switch on time to be proportional to the input voltage for at least
a portion of an alternating current (AC) cycle of the input
voltage.
[0043] A3. A device of aspect A1 or A2, wherein the input voltage
sensor and the variable switch on time generator are further
configured to determine the variable switch on time to be
proportional to the input voltage at times that the input voltage
is above a threshold minimum voltage, and to determine the variable
switch on time to be constant at a threshold minimum switch on time
at times that the input voltage is below the threshold minimum
voltage.
[0044] A4. A device of any of aspects A1-A3, wherein the input
voltage sensor comprises a minimum voltage clamp coupled to a power
input, wherein the minimum voltage clamp configures the input
voltage sensor to output a signal indicative of a minimum threshold
voltage to the variable switch on time generator in response to the
input voltage falling below a minimum threshold voltage.
[0045] A5. A device of any of aspects A1-A4, wherein the minimum
voltage clamp comprises an input pin coupled to a high voltage side
of the power input, and an alternative input pin coupled at least
in part to a low voltage side of the power input.
[0046] A6. A device of any of aspects A1-A5, wherein the
alternative input pin is coupled via the low voltage side of the
power input to a capacitor that is coupled on its opposing side to
the high voltage side of the power input.
[0047] A7. A device of any of aspects A1-A6, wherein the variable
on time generator comprises an on time measurement capacitor and a
controller input pin, wherein the variable on time generator is
configured to charge the on time measurement capacitor via the
voltage comparison pin until the on time measurement capacitor
reaches a voltage level of the controller input pin.
[0048] A.8. In another aspect A8 of this disclosure, a method
includes detecting an input voltage; determining a variable switch
on time based at least in part on the detected input voltage; and
outputting the determined switch on time for controlling switch on
timing of a driver switch.
[0049] A9. A method of aspect A8, further comprising determining
the variable switch on time to be proportional to the input voltage
for at leak a portion of an alternating current (AC) cycle of the
input voltage.
[0050] A10. A method of aspects A8 or A9, wherein determining the
variable switch on time further includes: determining the variable
switch on time to be proportional to the input voltage at times
that the input voltage is above a threshold minimum voltage; and
determining the variable switch on time to be constant at a
threshold minimum switch on time at times that the input voltage is
below the threshold minimum voltage.
[0051] A11. A method of any of aspects A8-A10, further including:
clamping a minimum threshold voltage in alternative to the input
voltage; and determining the variable switch on time based on the
minimum threshold voltage in response to the input voltage falling
below the minimum threshold voltage.
[0052] A12. A method of any of aspects A8-A11, wherein clamping the
minimum threshold voltage comprises receiving a voltage from a high
voltage side of a power input, and receiving an alternative voltage
at least in part from a low voltage side of the power input.
[0053] A13. A method of any of aspects A8-A12, wherein receiving an
alternative voltage further comprises receiving a voltage from a
capacitor that is coupled on its opposing side to the high voltage
side of the power input.
[0054] A14. A method of any of aspects A8-A13, wherein determining
the variable switch on time based at least in part on the detected
input voltage further comprises charging an on time measurement
capacitor via a voltage comparison pin until the on time
measurement capacitor reaches the detected input voltage.
[0055] A15. In another aspect A15 of this disclosure, a system is
configured to: detect an input voltage; determine a variable switch
on time based at least in part on the detected input voltage; and
output the determined switch on time for controlling switch on
timing of a driver switch.
[0056] A16. A system of aspect A15, comprising an input voltage
sensor configured to detect the input voltage.
[0057] A17. A system of aspects A15 or A16, comprising a variable
switch on time generator, operatively connected to the input
voltage sensor to receive a signal indicative of the input voltage,
the variable switch on time generator configured to determine the
variable switch on time based at least in part on the detected
input voltage, and output the determined switch on time for
controlling switch on timing of a driver switch.
[0058] A18. A system of any of aspects A15-A17, wherein the system
is further configured to determine the variable switch on time to
be proportional to the input voltage for at least a portion of an
alternating current (AC) cycle of the input voltage.
[0059] A19. A system of any of aspects A15-A18, wherein the system
is further configured such that determining the variable switch on
time further comprises:
[0060] determining the variable switch on time to be proportional
to the input voltage at times that the input voltage is above a
threshold minimum voltage; and
[0061] determining the variable switch on time to be constant at a
threshold minimum switch on time at times that the input voltage is
below the threshold minimum voltage.
[0062] A20. A system of any of aspects A15-A19, wherein the
variable on time generator comprises an on time measurement
capacitor and a controller input pin, wherein the variable on time
generator is configured to charge the on time measurement capacitor
via the voltage comparison pin until the on time measurement
capacitor reaches a voltage level of the controller input pin.
[0063] Various examples of the invention have been described. These
and other examples are within the scope of the following
claims.
* * * * *