U.S. patent application number 16/145053 was filed with the patent office on 2020-04-02 for arbitrary-ratio analog current division circuit.
This patent application is currently assigned to Lumileds LLC. Invention is credited to Yifeng Qiu.
Application Number | 20200107418 16/145053 |
Document ID | / |
Family ID | 69723576 |
Filed Date | 2020-04-02 |
United States Patent
Application |
20200107418 |
Kind Code |
A1 |
Qiu; Yifeng |
April 2, 2020 |
ARBITRARY-RATIO ANALOG CURRENT DIVISION CIRCUIT
Abstract
A circuit for dividing a single current source into two or more
current channels is disclosed. The circuit may comprise a voltage
controlled current source, a first sense resistor to sense a first
sensed voltage of a first current channel, a second sense resistor
to sense a second sensed voltage of a second current channel, a
computational device configured to compare the first sensed voltage
to the second sensed voltage to determine an output voltage, a
first voltage control switch to power a first LED array, a second
voltage control switch to power a second LED array, wherein the
output voltage is supplied to the first control switch. The
computational device may be a computational circuit or a
microcontroller.
Inventors: |
Qiu; Yifeng; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumileds LLC |
San Jose |
CA |
US |
|
|
Assignee: |
Lumileds LLC
San Jose
CA
|
Family ID: |
69723576 |
Appl. No.: |
16/145053 |
Filed: |
September 27, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/24 20200101;
H05B 45/46 20200101; H05B 45/37 20200101; H05B 45/395 20200101 |
International
Class: |
H05B 33/08 20060101
H05B033/08 |
Claims
1. A device comprising: a voltage controlled current source; a
first sense resistor to sense a first sensed voltage of a first
current channel; a second sense resistor to sense a second sensed
voltage of a second current channel; a computational circuit
comprising: an operational amplifier, and an RC circuit disposed
between an output of the operational amplifier and ground, the RC
circuit comprising a capacitor and resistor in parallel with the
capacitor, the operational amplifier configured to: provide a
charging current to charge the capacitor to increase an output
voltage of the computational circuit when the first sensed voltage
is less than the second sensed voltage, and allow the capacitor to
discharge through the resistor to decrease the output voltage when
the first sensed voltage is greater than the second sensed voltage;
a first voltage control switch to power, using the voltage
controlled current source, a first LED array based on the output
voltage of the computational circuit; and a second voltage control
switch to power, using the voltage controlled current source, a
second LED array based on the output voltage of the computational
circuit.
2. The device of claim 1, further comprising a second operational
amplifier coupled to the output voltage of the computational
circuit and the first voltage control switch.
3. The device of claim 1, further comprising a shunt regulator
coupled to a gate of the second voltage control switch.
4. The device of claim 3, wherein the shunt regulator has an
internal reference voltage of 2.5V.
5. The device of claim 1, wherein the first LED array has a
correlated color temperature (CCT) at a first tunable range and the
second LED array has a CCT at a second tunable range.
6-7. (canceled)
8. A device comprising: a voltage controlled current source; a
first sense resistor to sense a first sensed voltage of a first
current channel; a second sense resistor to sense a second sensed
voltage of a second current channel; a microcontroller configured
to: determine a ratio of the first sensed voltage to the second
sensed voltage to generate an output voltage, map a control signal
to the ratio, direct input current to the first current channel
when the control signal is at most a first predetermined voltage;
direct the input current to the second current channel when the
control signal is at least a second predetermined voltage; and
scale the input current between the first and second current
channels when the control signal is between the first and second
predetermined voltages; a first voltage control switch to power,
using the voltage controlled current source, a first LED array; a
second voltage control switch to power, using the voltage
controlled current source, a second LED array, the output voltage
to be supplied to the first voltage control switch.
9. The device of claim 8, further comprising an operational
amplifier coupled to the output voltage and the first voltage
control switch.
10. The device of claim 8, further comprising a shunt regulator in
the gate control circuit coupled to a gate of the second voltage
control switch.
11. The device of claim 10, wherein the shunt regulator has an
internal reference voltage of 2.5V.
12. The device of claim 8, wherein the first LED array has a
correlated color temperature (CCT) at a first tunable range and the
second LED array has a CCT at a second tunable range.
13-14. (canceled)
15. The device of claim 8, wherein: the control signal has a range
of 0-10y; the first predetermined voltage is 1V; and the second
predetermined voltage is 8V.
16. The device of claim 8, wherein the microcontroller continually
adjusts the output voltage.
17. A method comprising: receiving an input current from a voltage
controlled current source; sensing a first sensed voltage from a
first current channel; sensing a second sensed voltage from a
second current channel; calculating a ratio of the first sensed
voltage to the second sensed voltage to determine an output
voltage; mapping a control signal to the ratio; directing the input
current to the first current channel when the control signal is at
most a first predetermined voltage; directing the input current to
the second current channel when the control signal is at least a
second predetermined voltage; scaling the input current linearly
between the first and second current channel when the control
signal is between the first and second predetermined voltage; and
supplying the output voltage to the first current channel to power
a first LED array.
18. The method of claim 17, further comprising increasing the
output voltage when the first sensed voltage is less than the
second sensed voltage and decreasing the output voltage when the
first sensed voltage is greater than the second sensed voltage.
19-20. (canceled)
21. The device of claim 2, wherein an output of the second
operational amplifier is coupled to a gate of the first voltage
control switch.
22. The device of claim 21, further comprising a shunt regulator
coupled to a gate of the second voltage control switch, the output
of the second operational amplifier coupled to a reference node of
the shunt regulator through a voltage divider such that when a
voltage applied at the reference node is greater than a
predetermined shunt voltage, the shunt regulator is configured to
sink a current sufficient to pull the gate of the second voltage
control switch below a predetermined threshold and switch the
second voltage control switch off, and when the voltage applied at
the reference node is smaller than the predetermined shunt voltage,
the shunt regulator is configured to sink a quiescent current such
that a voltage at the gate of the second voltage control switch is
above the predetermined threshold and the second voltage control
switch is switched on.
23. The device of claim 1, wherein the computational circuit
further comprises a computational circuit switch having a gate
coupled with the output of the operational amplifier and a source
coupled with the RC circuit such that the computational circuit
switch is on when the first sensed voltage is less than the second
sensed voltage and off when the first sensed voltage is greater
than the second sensed voltage.
24. The device of claim 1, further comprising a plurality of
regulated current channels that is one fewer than a total number of
current channels, the first current channel being one of the
regulated current channels and the second current channel being an
unregulated current channel.
25. The device of claim 8, wherein the microcontroller is
configured to scale the input current at least one of linearly or
in a staircased manner between the first and second current
channels when the control signal is between the first and second
predetermined voltages.
26. The device of claim 25, further comprising: a shunt regulator
coupled to a gate of the second voltage control switch, an output
of the operational amplifier coupled to: a gate of the first
voltage control switch, and a reference node of the shunt regulator
through a voltage divider such that: when a voltage applied at the
reference node is greater than a predetermined shunt voltage, the
shunt regulator is configured to sink a current sufficient to pull
the gate of the second voltage control switch below a predetermined
threshold and switch the second voltage control switch off, and
when the voltage applied at the reference node is smaller than the
predetermined shunt voltage, the shunt regulator is configured to
sink a quiescent current such that a voltage at the gate of the
second voltage control switch is above the predetermined threshold
and the second voltage control switch is switched on.
Description
FIELD OF INVENTION
[0001] The present invention relates to a division circuit, and
more particularly to an analog current division circuit.
BACKGROUND
[0002] An LED circuit capable of dividing a current into two or
more channels of equal or unequal proportions provides certain
advantages. For example, multiple LED channels of different colors
may share a single channel LED driver in a correlated color
temperature (CCT) tuning system without the need for multi-channel
DC/DC converters.
[0003] In general, there are two approaches to current division.
The first method is the time-division method. In the time division
method, each channel conducts the full amplitude of the input
current within the allocated time slot. The second method is
dividing the current by amplitude. The second method operates in
the analog domain and creates multiple currents of small
amplitudes, the sum of which is equal to that of the input current.
Dividing a current by amplitude provides certain advantages,
including but not limited to, avoiding switching noise and
maximizing the utilization of LEDs, thereby increasing the
efficacy.
[0004] In general, analog current division in LEDs achieved though
parallel LED arrays. Resistors are connected in series on each
array in order to linearize the forward voltage. Parallel LED
arrays are best driven with equal current so as to avoid current
hogging. Therefore the current must be divided into equal
proportions and the system can only deal with a very limited amount
of mismatch between the parallel LED arrays.
[0005] It would be beneficial to provide an LED circuit capable of
dividing a current into two or more channels via parallel LED
arrays in which the current is divided into arbitrary rations and
can deal with a large mismatch between the parallel LED arrays.
SUMMARY
[0006] Circuits and methods for dividing a single current source
into two or more current channels are provided. The circuits and
method of the present disclosure allow a single current source to
be divided into arbitrary ratios and can tolerate a large mismatch
between the current channels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a chromaticity diagram representing a color
space;
[0008] FIG. 2 is a diagram illustrating different correlated color
temperatures (CCTs) and their relationship to a black body line
(BBL) on the chromaticity diagram;
[0009] FIG. 3 is a circuit diagram of a current division circuit of
the present disclosure;
[0010] FIG. 4 is a circuit diagram of a computational circuit that
may be used with the analog current division circuit of FIG. 3
[0011] FIG. 5 is a microcontroller that may be used with the
current division circuit of FIG. 3.
[0012] FIG. 6 is graph of a control signal that is fed into the
microcontroller of FIG. 5.
[0013] FIG. 7 is a flowchart illustrating a method for analog
circuit division.
[0014] FIG. 8 is a flowchart illustrating another method for analog
circuit division.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] In the following description, numerous specific details are
set forth, such as particular structures, components, materials,
dimensions, processing steps, and techniques, in order to provide a
thorough understanding of the present embodiments. However, it will
be appreciated by one of ordinary skill of the art that the
embodiments may be practiced without these specific details. In
other instances, well-known structures or processing steps have not
been described in detail in order to avoid obscuring the
embodiments. It will be understood that when an element such as a
layer, region, or substrate is referred to as being "on" or "over"
another element, it can be directly on the other element or
intervening elements may also be present. In contrast, when an
element is referred to as being "directly on" or "directly" over
another element, there are no intervening elements present. It will
also be understood that when an element is referred to as being
"beneath," "below," or "under" another element, it can be directly
beneath or under the other element, or intervening elements may be
present. In contrast, when an element is referred to as being
"directly beneath" or "directly under" another element, there are
no intervening elements present.
[0016] In the interest of not obscuring the presentation of
embodiments in the following detailed description, some processing
steps or operations that are known in the art may have been
combined together for presentation and for illustration purposes
and in some instances may have not been described in detail. In
other instances, some processing steps or operations that are known
in the art may not be described at all. It should be understood
that the following description is rather focused on the distinctive
features or elements of various embodiments described herein.
[0017] Referring to FIG. 1, a chromaticity diagram representing a
color space is shown. A color space is a three-dimensional space;
that is, a color is specified by a set of three numbers that
specify the color and brightness of a particular homogeneous visual
stimulus. The three numbers may be the International Commission on
Illumination (CIE) coordinates X, Y, and Z, or other values such as
hue, colorfulness, and luminance. Based on the fact that the human
eye has three different types of color sensitive cones, the
response of the eye is best described in terms of these three
"tristimulus values."
[0018] A chromaticity diagram is a color projected into a
two-dimensional space that ignores brightness. For example, the
standard CIE XYZ color space projects directly to the corresponding
chromaticity space specified by the two chromaticity coordinates
known as x and y, as shown in FIG. 1.
[0019] Chromaticity is an objective specification of the quality of
a color regardless of its luminance. Chromaticity consists of two
independent parameters, often specified as hue and colorfulness,
where the latter is alternatively called saturation, chroma,
intensity, or excitation purity. The chromaticity diagram may
include all the colors perceivable by the human eye. The
chromaticity diagram may provide high precision because the
parameters are based on the spectral power distribution (SPD) of
the light emitted from a colored object and are factored by
sensitivity curves which have been measured for the human eye. Any
color may be expressed precisely in terms of the two color
coordinates x and y.
[0020] All colors within a certain region, known as a MacAdam
ellipse (MAE) 102, may be indistinguishable to the average human
eye from the color at the center 104 of the ellipse. The
chromaticity diagram may have multiple MAEs. Standard Deviation
Color Matching in LED lighting uses deviations relative to MAEs to
describe color precision of a light source.
[0021] The chromaticity diagram includes the Planckian locus, or
the black body line (BBL) 106. The BBL 106 is the path or locus
that the color of an incandescent black body would take in a
particular chromaticity space as the blackbody temperature changes.
It goes from deep red at low temperatures through orange, yellowish
white, white, and finally bluish white at very high temperatures.
Generally speaking, human eyes prefer white color points not too
far away from the BBL 106. Color points above the black body line
would appear too green while those below would appear too pink.
[0022] One method of creating white light using light emitting
diodes (LEDs) may be to additively mix red, green and blue colored
lights. However, this method may require precise calculation of
mixing ratios so that the resulting color point is on or close to
the BBL 106. Another method may be to mix two or more phosphor
converted white LEDs of different correlated color temperatures
(CCTs). This method is described in additional detail below.
[0023] To create a tunable white light engine, LEDs having two
different CCTs on each end of a desired tuning range may be used.
For example, a first LED may have a CCT of 2700K, which is a warm
white, and a second LED may have a color temperature of 4000K,
which is a neutral white. White colors having a temperature between
2700K and 4000K may be obtained by simply varying the mixing ratio
of power provided to the first LED through a first channel of a
driver and power provided to the second LED through a second
channel of the driver.
[0024] Referring now to FIG. 2, a diagram illustrating different
CCTs and their relationship to the BBL 106 is shown. When plotted
in the chromaticity diagram, the achievable color points of mixing
two LEDs with different CCTs may form a first straight line 202.
Assuming the color points of 2700K and 4000K are exactly on the BBL
106, the color points in between these two CCTs would be below the
BBL 106. This may not be a problem, as the maximum distance of
points on this line from the BBL 106 may be relatively small.
[0025] Dividing one current sink or current source into N channels
essentially creates N current sinks or N current sources. According
to Kirchhoff's current laws, the sum of all the currents flowing
into one node must be zero. As such, at any node in an electrical
circuit, the sum of currents flowing into that node is equal to the
sum of currents flowing out of that node. Stated another way, the
algebraic sum of currents in a network of conductors meeting at a
point is zero. This principle may be stated as the following
equation:
.SIGMA..sub.k=1.sup.nI.sub.k=0. Equation (1)
[0026] However, in practice it is nearly impossible to create N
regulated currents whose sum is precisely equal to the input
current being divided. This is because, in general, the input
current is not known.
[0027] Referring to FIG. 3, a circuit diagram of a current division
circuit 300 is shown. The current division circuit 300 makes use of
various analog techniques, such as voltage sensing, voltage control
current source, and negative feedback.
[0028] As described in more detail below, the current division
circuit of the present disclosure may enable dividing an input
current into two or more current channels. The current division
circuit of the present disclosure comprises at least one regulated
current channel and the number of regulated current channels is one
less than the total number of current channels. For example, if
there is a total of three current channels, there can only be two
regulated current channels.
[0029] In an embodiment, the current division circuit may be
mounted on a converter printed circuit board (PCB) between an LED
driver 301 and a LED board. The LED driver 301 may be a
conventional LED driver known in the art. The current division
circuit may allow the LED driver 301 to be used for applications
requiring two or more LED arrays. For example, the LED driver 301
of current division circuit 300 may be used to power a first LED
array 311 and a second LED array 321.
[0030] In an embodiment, the LED driver 301 is used to power two
LED arrays having different CCTs. In other embodiments, the two LED
arrays may have different color ranges, infrared (IR) ranges, and
ultraviolet (UV) ranges.
[0031] Each current channel of the current division circuit
comprises a sense resistor. For example, in an embodiment with two
current channels, the current division circuit comprises a first
sense resistor (R.sub.s1) 312 to sense a first sensed voltage of
the first current channel 310 at V.sub.sense1 313 and a second
sense resistor (R.sub.s2) 322 to sense a second voltage of the
second current channel 320 at V.sub.sense2 323. The voltage at
V.sub.sense1 313 is representative of the current flowing through
the first sense resistor (R.sub.s1) 312 and the voltage at
V.sub.sense2 323 is representative of the current flowing through
the second sense resistor (R.sub.s2) 322.
[0032] The current division circuit 300 of the present disclosure
further comprises a computational device (not shown). The
computational device is configured to compare the first sensed
voltage (V.sub.sense1) 313 and the second sensed voltage
(V.sub.sense2) 323 to determine a set voltage (V.sub.set) 350. If
the first sensed voltage (V.sub.sense1) 313 is lower than the
second sensed voltage .DELTA.(V.sub.sense2) 323, the computational
device is configured to increase V.sub.set. If the first sensed
voltage (V.sub.sense1) device is greater than the second sensed
voltage (V.sub.sense2) 323, the computational device is configured
to decrease the set voltage (V.sub.set) 350.
[0033] The set voltage (V.sub.set) 350 may be fed to a voltage
controlled current source, which may be implemented with a first
operational amplifier (opamp) 330. The first opamp 330 may provide
a first gate voltage (V.sub.g1) 314. The first gate voltage
(V.sub.g1) 314 may be input to a first transistor (M1) 315 that is
used to provide a driving current for the first LED array 311. The
first transistor (M1) 315 may be a conventional metal oxide
semiconductor field effect transistor (MOSFET). The first
transistor M1 may be an n-channel MOSFET.
[0034] A second transistor (M2) 325 may control power to the second
LED array 321. The second transistor (M2) 325 may be a conventional
metal oxide semiconductor field effect transistor (MOSFET). The
second transistor M2 may be an n-channel MOSFET. The second
transistor (M2) 325 may only be switched on when the first circuit
channel 310 is in regulation. A second gate voltage (V.sub.g2) 324
may flow through the second transistor (M2) 325.
[0035] The second gate voltage (V.sub.g2) 324 may be fed to a REF
input of a shunt regulator 340. In an embodiment, the shunt
regulator 340 has an internal reference voltage of 2.5V. When the
voltage applied at the REF node is higher than 2.5V, the shunt
regulator 140 may sink a large current. When the voltage applied at
the REF node is lower than 2.5V, the first shunt regulator may sink
a very small quiescent current.
[0036] The large sinking current may pull the gate voltage of the
second transistor (M2) 325 down to a level below its threshold,
which may switch off the second transistor (M2) 325. The shunt
regulator 340 may not be able to pull their cathodes more than the
forward voltage (V.sub.f) of a diode below their REF nodes.
Accordingly, the second transistor (M2) 325 may have a threshold
voltage that is higher than 2.5V. Alternatively, a shunt regulator
with a lower internal reference voltage, such as 1.24V, may be
used.
[0037] Referring to FIG. 4, the computational device may be a
computational circuit 400. The computational circuit 400 may
comprise a second opamp 430, a capacitor 440 between the location
of the set voltage (V.sub.set) 350 and the ground, and a resistor
450 in parallel to the capacitor 440. The first sensed voltage
(V.sub.sense1) 313 and the second sensed voltage (V.sub.sense2) 323
are fed to the second op amp 430. The computational circuit 400 may
be configured to compare the first sensed voltage (V.sub.sense1)
313 to the second sensed voltage (V.sub.sense2) 323 by subtracting
the first sensed voltage (V.sub.sense1) 313 from the second sensed
voltage (V.sub.sense2) 323.
[0038] When the second opamp 430 is in regulation, the
computational circuit 400 may be configured to convert the
difference of the first sensed voltage (V.sub.sense1) 313 and the
second sensed voltage (V.sub.sense2) 323 into a charging current to
charge the capacitor 440 to increase the set voltage (V.sub.set)
350 when the first sensed voltage (V.sub.sense1) 313 is less than
the second sensed voltage (V.sub.sense2) 323. The computational
circuit 400 may be configured to convert the difference of the
first sensed voltage (V.sub.sense1) 313 and the second sensed
voltage (V.sub.sense2) 323 into a discharging resistor 450 to
decrease the set voltage (V.sub.set) 350 when the first sensed
voltage (V.sub.sense1) 313 is greater than the second sensed
voltage (V.sub.sense2) 323.
[0039] Therefore, if the first sensed voltage (V.sub.sense1) 313 is
higher than the second sensed voltage (V.sub.sense2) 323, the
computational circuit 400 may decrease the set voltage (V.sub.set)
350 which in turn decreases the first gate voltage (V.sub.g1) 314
which supplies power to the first current channel 310. Stated
another way, when the second opamp 430 is in regulation, the first
sensed voltage (V.sub.sense1) 313 is approximately equal to second
sensed voltage (V.sub.sense2) 323. Therefore during steady state,
the ratio of the current of the first current channel 310 to the
current of the second current channel 320 is equal to the value of
the second sense resistor (R.sub.s2) 322 to the value of the first
sense resistor (R.sub.s1) 312, and the following equations are
satisfied:
I Rs 1 = V set R s 1 ; Equation ( 2 ) I Rs 2 = V set R s 2 .
Equation ( 3 ) ##EQU00001##
[0040] Therefore, when the value of the first sense resistor
(R.sub.s1) 312 equals the value of the second sense resistor
(R.sub.s2) 322, the current flowing through the first resistor
(I.sub.Rs1) equals the current flowing through the second resistor
(I.sub.Rs2) and the current division circuit 300 divides the
current into two equal parts, assuming the current drawn by the
auxiliary circuits, such as supply voltage generation, is
negligible.
[0041] It should be noted that the computational circuit 400 should
be tested for closed-loop behavior and stability and adjusted
accordingly.
[0042] It should further be noted that, as will be appreciated by
one having ordinary skill in the art, the computational circuit 400
illustrated in FIG. 4 is one of many possible implementations.
[0043] As previously noted, the current division circuit 300 may be
divided into three or more channels. For example, the first current
channel 310 may be replicated so that there is a first current
channel, a second current channel, and a third current channel. The
first current channel and the second current channel would be
regulated current channels, such as the first current channel 310
of the current division circuit 300 shown in FIG. 3. The third
current channel would not be regulated and would resemble the
second current channel 320 of the current division circuit 300
shown in FIG. 3.
[0044] It should also be noted that the computational circuit 400
illustrated in FIG. 4 may become complicated for circuit division
circuits dividing one current source into three or more current
channels. As such, the computation circuit illustrated in FIG. 4
may be replaced with a microcontroller.
[0045] Referring to FIG. 5, in one embodiment, the computational
device may be a microcontroller 500, which can handle complex
signal processing with less PCB resources than analog circuits. The
microcontroller 500 digitizes three analog signals with its
internal ADC: the first sensed voltage (V.sub.sense1) 313, the
second sensed voltage (V.sub.sense2) 323, and a control signal 501.
As the value of the first sense resistor (R.sub.s1) 312 and the
value of the second sense resistor (R.sub.s2) 322 are known, the
total input current is determined using the following equation:
I total = Vsense 1 Rs 1 + Vsense 2 R s 2 . Equation ( 4 )
##EQU00002##
[0046] Referring to FIG. 6, a ratio of the first sensed voltage
(V.sub.sense1) 313 to the second sensed voltage (V.sub.sense2) 323
is modulated by a control signal 501 of the microcontroller. The
microcontroller calculates the ratio of the first sensed voltage
(V.sub.sense1) 313 to the second sensed voltage (V.sub.sense2) 323.
The control signal 501 is mapped to the ratio of the first sensed
voltage (V.sub.sense1) 313 to the second sensed voltage
(V.sub.sense2) 323. When the control signal 501 is less than or
equal to a first predetermined voltage 601, all of the input
current is directed to the first current channel. When the control
signal 501 is greater than or equal to a second predetermined
voltage 602, all of the input current is directed to the second
current channel. When the control signal 501 is between the first
predetermined voltage 601 and the second predetermined voltage 602,
the current may be scaled linearly between the first current
channel and the second current channel. The current may also be
scaled according to other curves and knee points. For example,
between the first predetermined voltage 601 and the second
predetermined 602 threshold the current may be staircased to
provide stepped control.
[0047] In one embodiment, the control signal 501 has a range of
0-10V and the first predetermined voltage is 1V and the second
predetermined voltage is 8V. Therefore, when the 0-10V control
signal is less than or equal to 1V, all of the input current goes
to the first current channel. When the 0-10V signal is greater than
or equal to 8V, all of the input current goes to the second current
channel. When the 0-10V signal is between 1V and 8V, the current is
scaled linearly between the two channels.
[0048] The choice of the value of the first resistor (R.sub.s1) 312
and the value of the second resistor (R.sub.s2) 322 is a trade-off
between resolution and power consumption. For the same current, the
higher the value of the first resistor (R.sub.s1) 312 and the value
of the second resistor (R.sub.s2) 322, the higher the first sensed
voltage (V.sub.sense1) 313 and the second sensed voltage
(V.sub.sense2) 323 are. A higher first sensed voltage
(V.sub.sense1) 313 and second sensed voltage (V.sub.sense2) 323
allow the use of cheaper and less precise electrical circuits at
the cost of increased power dissipation and reduced efficiency. If
the value of the first resistor (R.sub.s1) 312 is too large, it may
be necessary to choose a larger MOSFET in order to have a lower
internal resistance (Rds(on)). Additionally or alternatively, if
the value of the first resistor (R.sub.s1) 312 is too large, it may
be necessary to have a higher supply voltage (V.sub.dd), which
makes it necessary to choose signal processing circuits capable of
running at a higher voltage. This may potentially increase the cost
of the circuit.
[0049] It should be noted that well-known structures shown in FIGS.
3 and 4, including one or more resistors, diodes, and capacitors,
and processing steps have not been described in detail in order to
avoid obscuring the embodiments described herein.
[0050] Referring now to FIG. 7, a flowchart illustrating a method
for analog circuit division is shown. At step 701, an input current
is received from a voltage controlled current source, such as an
LED driver. At step 702, a first sensed voltage of a first current
channel is sensed. At step 703, a second voltage of a second
current channel is sensed. At step 704, the first sensed voltage
and the second sensed voltage are compared to determine an output
voltage. At step 705, if the first sensed voltage is lower than the
second sensed voltage, the output voltage increases. If the first
sensed voltage is higher than the second sensed voltage, output
voltage decreases. At step 706, the output voltage is provided to
the first current channel to power a first LED array. At step 707,
the current that is left over after the first LED array has taken
its share is automatically provided to the second current channel
to power a second LED array.
[0051] The method shown in FIG. 7 may be performed by the current
division circuit 300 utilizing the computational circuit 400
illustrated in FIG. 4. For example, at step 701, an input current
may be received from the LED driver 301. At step 702, the first
sense resistor (R.sub.s1) 312 may sense a first sensed voltage
(V.sub.sense1) 313 of the first current channel 310. At step 702,
the second sense resistor (R.sub.s2) 322 may sense a second sensed
voltage (V.sub.sense) of the second current channel 320. At step
704, the first sensed voltage (V.sub.sense1) 313 and the second
sensed voltage (V.sub.sense2) 323 may be fed into the second op amp
430 of the computational circuit 400 which compares the first
sensed voltage (V.sub.sense1) 313 and the second sensed voltage
(V.sub.sense2) 323 by subtracting the first sensed voltage
(V.sub.sense1) 313 from the second sensed voltage (V.sub.sense2)
323. At step 705, the computational circuit 400 may convert the
difference of the first sensed voltage (V.sub.sense1) 313 and the
second sensed voltage (V.sub.sense2) 323 into a charging current to
charge the capacitor 440 to increase the set voltage (V.sub.set)
350 when the first sensed voltage (V.sub.sense1) 313 is less than
the second sensed voltage (V.sub.sense2) 323. Further, the
computational circuit 400 may convert the difference of the first
sensed voltage (V.sub.sense1) 313 and the second sensed voltage
(V.sub.sense2) 323 into a discharging resistor 450 to decrease the
set voltage (V.sub.set) 350 when the first sensed voltage
(V.sub.sense1) 313 is greater than the second sensed voltage
(V.sub.sense2) 323. The set voltage (V.sub.set) 350 may then be
supplied to the first current channel 310 to power the first LED
array 311. The current that is left over after the first LED array
311 has taken its share is automatically provided to the second
current channel 320 to power a second LED array 321.
[0052] Referring now to FIG. 8, a flowchart illustrating a method
for analog circuit division performed by a current division circuit
comprising a microcontroller is shown. At step 801, an input
current is received from a voltage controlled current source, such
as an LED driver. At step 802, a first sensed voltage of a first
current channel is sensed. At step 803, a second voltage of a
second current channel is sensed. At step 804, a ratio of the first
sensed voltage to the second sensed voltage is determined. At step
805, a control signal is mapped to the ratio of the first sensed
voltage of the second sensed voltage. At step 806, when the signal
is less than or equal to a first predetermined voltage, all of the
input current is directed to the first current channel. If the
signal is greater than or equal to a second predetermined voltage,
all of the input current is directed to the second current channel.
If the signal is between the first predetermined voltage and the
second predetermined voltage, the current is scaled between the
first current channel and the second current channel.
[0053] The method shown in FIG. 8 may be performed by the current
division circuit 300 utilizing the microcontroller 500 illustrated
in FIG. 5. For example, at step 801, an input current may be
received from the LED driver 301. At step 802, the first sense
resistor (R.sub.s1) 312 may sense a first sensed voltage
(V.sub.sense1) 313 of the first current channel 310. At step 803,
the second sense resistor (R.sub.s2) 322 may sense a second sensed
voltage (V.sub.sense) of the second current channel 320. At step
804, the first sensed voltage (V.sub.sense1) 313, the second sensed
voltage (V.sub.sense2) 323, and the control signal 501 are fed into
the microcontroller 500 which determines a ratio of the first
sensed voltage to the first sensed voltage (V.sub.sense1) 313 to
the second sensed voltage (V.sub.sense2) 323. At step 805, the
microcontroller maps the ratio of the first sensed voltage
(V.sub.sense1) 313 to the second sensed voltage (V.sub.sense2) 323.
At step 806, the microcontroller directs all of input current to
the first current channel 310 if signal is less than or equal to a
first predetermined voltage 601, directs all of input current to
second current channel 320 if the control signal 501 is greater
than or equal to a second predetermined voltage 60, and scales the
current between the first current channel 310 and the second
current channel 320 if the control signal 501 is between the first
predetermined voltage 601 and the second predetermined voltage
602.
[0054] Although features and elements are described above in
particular combinations, one of ordinary skill in the art will
appreciate that each feature or element can be used alone or in any
combination with the other features and elements. In addition, the
methods described herein may be implemented in a computer program,
software, or firmware incorporated in a computer-readable medium
for execution by a computer or processor. Examples of
computer-readable media include electronic signals (transmitted
over wired or wireless connections) and computer-readable storage
media. Examples of computer-readable storage media include, but are
not limited to, a read only memory (ROM), a random access memory
(RAM), a register, cache memory, semiconductor memory devices,
magnetic media such as internal hard disks and removable disks,
magneto-optical media, and optical media such as CD-ROM disks, and
digital versatile disks (DVDs).
[0055] Having described the invention in detail, those skilled in
the art will appreciate that, given the present disclosure,
modifications may be made to the invention without departing from
the spirit of the inventive concepts described herein. Therefore,
it is not intended that the scope of the invention be limited to
the specific embodiments illustrated and described.
* * * * *