CN101193476A - Control device for controlling a plurality of light emitting diode strings and related light source module - Google Patents

Abstract

The invention relates to a control device for controlling a plurality of light emitting diode serials and a related light source module, wherein the first ends of the plurality of light emitting diode serials are all electrically connected with a working voltage. One of the control devices proposed in the present invention comprises: a plurality of transistors, each having a control terminal, a first terminal and a second terminal, wherein the first terminal of each transistor is electrically connected to the second terminal of a corresponding one of the plurality of led strings, and the second terminals of the plurality of transistors are grounded through a plurality of impedance elements, respectively; and the transistor controller is electrically connected to the control ends of the plurality of transistors and used for adjusting the input signal of the control end of each transistor according to the voltage of the second end of each transistor so as to control the current of the first end of each transistor.

Description

A control device for controlling a plurality of light-emitting diode strings and related light source modules

technical field

The invention relates to the technology of controlling light emitting diodes, in particular to a control device for controlling a series of light emitting diodes and a related light source module.

Background technique

The use of light emitting diodes (LEDs) as light sources is becoming more and more common. For example, most of the backlight modules of traditional liquid crystal display panels use cold cathode fluorescent lamps (cold cathode fluorescent lamp, CCFL) as light sources. Nowadays, as the luminous efficiency of light-emitting diodes continues to increase and the cost decreases, light-emitting diodes tend to replace CCFLs as light sources for backlight modules.

In the known technology, a plurality of light-emitting diodes are often connected in series to reduce the number of driving circuits required and the total driving current of the light-emitting diodes. However, due to manufacturing process variations, it is difficult to ensure that all LEDs in different strings have completely consistent device parameters. In addition, environmental factors such as temperature may also affect the component parameters of light emitting diodes. For example, the forward voltage (VF) of different light emitting diodes often has slight differences. The structure of connecting multiple LEDs in series will add up the forward voltage errors of all LEDs in the same string, and the total accumulated forward voltage errors of different LED strings will usually be different .

In this case, even if the same operating voltage is applied to different LED strings, the current flowing through individual LED strings will be different due to the difference in the total forward voltage error accumulated by each LED string . In this way, the LED strings will have different luminances due to the current inconsistency. Therefore, when the LED series is used as the light source of the backlight module of the liquid crystal display panel, the liquid crystal display panel will often cause the undesirable phenomenon of color unevenness (Mura) due to uneven brightness of the backlight.

Contents of the invention

In view of this, one of the objectives of the present invention is to provide a control device capable of controlling the brightness of a plurality of LED strings and a related light source module, so as to solve the above-mentioned problems.

The present invention provides a control device for controlling a plurality of LED strings, wherein the first ends of the multiple LED strings are electrically connected to an operating voltage. The control device includes: a plurality of transistors, each It has a control terminal, a first terminal and a second terminal, wherein the first terminal of each transistor is electrically connected to the second terminal of a corresponding series in the plurality of LED series, and the first terminal of the plurality of transistors The two terminals are respectively grounded through a plurality of impedance elements; and the transistor controller is electrically connected to the control terminals of the plurality of transistors, and is used to adjust the input signal of the control terminal of each transistor according to the voltage of the second terminal of each transistor, so as to controls the current at the first terminal of the transistor.

The present invention also provides a light source module, which includes: a plurality of light emitting diode series, each having a first end and a second end, and the first ends of the plurality of light emitting diode series are all electrically connected to the working voltage a plurality of transistors, each having a control terminal, a first terminal and a second terminal, wherein the first terminal of each transistor is electrically connected to the second terminal of a corresponding series in the plurality of LED series, and The second ends of the plurality of transistors are respectively grounded through a plurality of impedance elements; the error calculation circuit is electrically connected to the second ends of the plurality of transistors, and is used to calculate the voltage of the second end of each transistor and the corresponding reference voltage respectively difference; and a transistor controller, electrically connected to the error calculation circuit and the control terminals of the plurality of transistors, for controlling the current of the first terminal of each transistor according to the calculation result of the error calculation circuit.

Description of drawings

FIG. 1 is a simplified schematic diagram of an embodiment of a light source module of the present invention.

FIG. 2 is a simplified schematic diagram of an embodiment of the transistor controller in FIG. 1 .

[Description of main component labels]

100 Light source module

110a, 110b～110n LED series

120 Control device

130a, 130b～130n transistors

140 Error calculation circuit

150 Transistor Controller

160a, 160b～160n impedance element

210 Voltage source

220 variable resistor

230 decision units

Detailed ways

Please refer to FIG. 1 , which is a simplified schematic diagram of a light source module 100 according to an embodiment of the present invention. The light source module 100 includes a plurality of LED strings 110a˜110n, and a control device 120 for controlling the LED strings. In this embodiment, the first ends of the LED strings 110a-110n are all electrically connected to the operating voltage Vin, and the LED strings 110a-110n all have the same number of LEDs of the same color. The control device 120 in the light source module 100 is used to control the LED strings 110a-110n, so that the LED strings 110a-110n can have substantially the same brightness. As shown in FIG. 1 , the control device 120 includes: a plurality of transistors 130a-130n, an error calculation circuit 140, a transistor controller 150, and a plurality of impedance elements 160a-160n. In a preferred embodiment, the impedance elements 160 a - 160 n have substantially the same impedance value, for example, the impedance elements 160 a - 160 n can be respectively implemented by a plurality of resistance units having substantially the same resistance value. The operation of the control device 120 will be further described below.

The transistors 130 a - 130 n in the control device 120 of this embodiment are all bipolar junction transistors (bipolar junction transistors, BJT), and each transistor includes a control terminal, a first terminal and a second terminal. In this embodiment, the control terminal is a base, the first terminal is a collector and the second terminal is an emitter. As shown in FIG. 1 , the collectors of the transistors 130 a - 130 n are electrically connected to the second terminals of the LED strings 110 a - 110 n respectively, and the emitters of the transistors 130 a - 130 n are respectively grounded through impedance elements 160 a - 160 n. In practice, the transistors 130a˜130n should have substantially the same common-emitter current gain, and all operate in the active region, so as to improve performance and reduce control complexity, but this The actual implementation of the invention is not limited thereto.

As mentioned above, environmental factors such as manufacturing process deviation or temperature may cause differences in the accumulated total forward voltage errors of the individual LED strings 110 a - 110 n , thereby resulting in currents Ic1 , The sizes of Ic2~Icn are inconsistent. In this embodiment, the control device 120 uses the transistors 130a-130n to respectively control the currents Ic1-Icn of the LED strings 110a-110n, so that the brightness of these LED strings tends to be consistent.

Specifically, the control device 120 utilizes the error calculation circuit 140 to calculate the difference between the emitter voltage VFi of each of the transistors 130 a - 130 n and the corresponding reference voltage Vref. Preferably, the error calculation circuit 140 can amplify the difference between the emitter voltage VFi of each transistor and the reference voltage Vref, so as to improve the resolution of the feedback signal. In practice, the error calculation circuit 140 can be realized by one or more operational amplifiers. For example, the error calculation circuit 140 can be a single operational amplifier for sequentially calculating the difference between the emitter voltages of the transistors 130 a - 130 n and the reference voltage Vref. Alternatively, the error calculation circuit 140 can also use a plurality of operational amplifiers to simultaneously calculate the difference between the emitter voltages of the transistors 130 a - 130 n and the reference voltage Vref in parallel processing. For example, the error calculation circuit 140 can use a first operational amplifier (not shown) to calculate the difference between the emitter voltage VF1 of the transistor 130a and the reference voltage Vref, and simultaneously use a second operational amplifier (not shown) to calculate The difference between the emitter voltage VF2 of the transistor 130b and the reference voltage Vref, wherein the first and second operational amplifiers preferably have substantially the same gain.

The transistor controller 150 will adjust the base current Ibi of each of the transistors 130a-130n according to the calculation result of the error calculation circuit 140, so that the collector currents of the transistors 130a-130n (that is, flow through the LED series) The currents (Ic1˜Icn) of 110a˜110n can approach a predetermined value. The operation and implementation of the transistor controller 150 will be further described below with reference to FIG. 2 .

FIG. 2 is a simplified schematic diagram of an embodiment of the transistor controller 150 . Since the transistor controller 150 adjusts the base current and the collector current of each of the transistors 130a-130n in the same manner and structure, the following is only an example of the transistor controller 150 adjusting the base current Ib1 of the transistor 130a. Be explained. Wherein, except the transistor 130a and its corresponding LED string 110a and impedance element 160a in FIG. 2 , other transistors, LED strings, and impedance elements are omitted and not shown. As shown in FIG. 2, the transistor controller 150 of this embodiment includes a voltage source 210 for outputting a predetermined voltage Vd; a variable resistor 220 electrically connected between the voltage source 210 and the base of the transistor 130a; and a decision unit 230 , electrically connected to the error calculation circuit 140 and the variable resistor 220 , for changing the resistance value of the variable resistor 220 according to the calculation result of the error calculation circuit 140 to adjust the base current Ib1 of the transistor 130 a.

When the transistor 130a operates in the active region, the collector current Ic1 and the base current Ib1 have the following linear relationship:

Ic1=β×Ib1(1)

where β is the common emitter current gain of transistor 130a.

The operation of the error calculation circuit 140 to calculate the voltage difference Ver1 between the emitter voltage VF1 of the transistor 130a and the reference voltage Vref can be expressed by the following formula:

Ver1=A×(Vref-VF1)(2)

Where A is the gain of the error calculation circuit 140 .

Assuming that the resistance value of the variable resistor 220 is R1, the relationship between R1 and the base current Ib1 of the transistor 130a is as follows:

Ib1×R1=Ver1-(VF1+Vbe)(3)

Where Vbe is the voltage across the base and emitter of the transistor 130a. It can be seen from formula (3):

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Ib"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">Ib</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Ver</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="VF"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">VF</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Substituting formula (2) into formula (4) can get:

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Ib"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">Ib</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Vref</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; VF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="VF"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">VF</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; Vref</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; VF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Then, substituting formula (1) into formula (5) can get the following relationship:

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="IC"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">IC</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; Vref</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; VF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Assuming K1=β×A, K2=β×(A+1), since the gain A of the error calculation circuit 140 is usually much larger than 1, K1 and K2 will be very close. Therefore, formula (6) can be rewritten as the following formula:

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="IC"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">IC</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="K"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">K</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Vref</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; VF</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="K"\; filenames="A20061016253400121.png"\; state="\{\{state\}\}">K</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; Ver</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vbe</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

K1, Vbe, and β in formula (7) are all fixed values, therefore, the decision unit 230 in the transistor controller 150 can change the resistance value of the variable resistor 220 according to the calculation result Ver1 output by the error calculation circuit 140 R1 to adjust the base current Ib1 of the transistor 130a. In this way, the purpose of controlling the collector current Ic1 of the transistor 130a can be achieved. In this embodiment, the determination unit 230 controls the collector current Ic1 of the transistor 130 a within a predetermined value or within a predetermined range by adjusting the resistance value R1 of the variable resistor 220 . Likewise, the transistor controller 150 can use the same architecture to adjust the collector currents Ic2 -Icn of other transistors 130b - 130n in the control device 120 . In this way, the currents Ic1 , Ic2 ˜ Icn flowing through the LED strings 110 a ˜ 110 n tend to be consistent, so the situation that the brightness of the LED strings 110 a ˜ 110 n are not equal can be greatly improved.

From the above description, it can be seen that using the light source module 100 disclosed above as the light source of the backlight module of the liquid crystal display panel can effectively solve the phenomenon of color unevenness (Mura) of the liquid crystal display panel.

Although the light-emitting diodes included in each light-emitting diode series in the aforementioned light source module 100 are light-emitting diodes of the same color, this is only an example and does not limit the practical application scope of the present invention. In practice, the colors of the LED series 110 a - 110 n may also be different from each other. For example, the LED strings 110 a - 110 n may include at least one string of the first color and at least one string of the second color. In practice, the total forward voltage values of LED strings of different colors may be different. Therefore, the error calculation circuit 140 can use different reference voltages to compare the feedback voltages VFi corresponding to the LED strings of different colors. Alternatively, the decision unit 230 in the transistor controller 150 can set different target current values for LED strings of different colors, and use the aforementioned feedback control method to control the brightness performance of individual LED strings.

In addition, some or all of the bipolar junction transistor (BJT) transistors 130a˜130n in the aforementioned control device 120 can be replaced by a plurality of insulated-gate bipolar transistors (insulated-gate bipolar transistor, IGBT), and these insulated-gate bipolar transistors Polar transistors preferably have substantially the same conduction characteristics (Transconductance). For the IGBT, the control terminal is the gate, and the first terminal and the second terminal are the same as the bipolar junction transistor, which are respectively the collector and the emitter. In this architecture, the error calculation circuit 140 calculates the error value according to the emitter voltage of each IGBT, and the transistor controller 150 adjusts the IGBT according to the calculation result of the error calculation circuit 140 . The gate input voltage of the bipolar transistor is used to control the collector current of the IGBT.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims (26)

1. A control device for controlling a plurality of LED strings, wherein the first ends of the multiple LED strings are electrically connected to an operating voltage, the control device includes: A plurality of transistors all have a control terminal, a first terminal and a second terminal, wherein the first terminal of each transistor is electrically connected to the second terminal of a corresponding series in the plurality of light emitting diode series, and the The second ends of the plurality of transistors are respectively grounded through a plurality of impedance elements; and The transistor controller is electrically connected to the control terminals of the plurality of transistors, and is used for adjusting the input signal of the control terminal of each transistor according to the voltage of the second terminal of each transistor, so as to control the current of the first terminal of the transistor. 2. The control device according to claim 1, further comprising an error calculation circuit, electrically connected to the transistor controller and the second terminals of the plurality of transistors, for calculating the voltage of the second terminal of each transistor and the corresponding The difference between the reference voltages, wherein the transistor controller adjusts the input signal of the control terminal of the transistor according to the calculation result of the error calculation circuit. 3. The control device according to claim 2, wherein the error calculation circuit amplifies the difference between the voltage at the second terminal of each transistor and the reference voltage. 4. The control device according to claim 2, wherein the error calculation circuit comprises a first operational amplifier for calculating the difference between the voltages of the second terminals of the plurality of transistors and the reference voltage respectively. 5. The control device according to claim 4, wherein the error calculation circuit further comprises a second operational amplifier for calculating a difference between a voltage at a second terminal of a second transistor among the plurality of transistors and the reference voltage. 6. The control device according to claim 5, wherein the first and second operational amplifiers have substantially the same gain. 7. The control device according to claim 1, wherein the plurality of transistors are all bipolar transistors. 8. The control device according to claim 7, wherein the plurality of transistors have substantially the same common emitter current gain. 9. The control device according to claim 7, wherein the transistor controller comprises: a voltage source for outputting a predetermined voltage; a variable resistor electrically connected between the voltage source and a control terminal of a corresponding transistor of the plurality of transistors; and The determination unit is electrically connected to the error calculation circuit and the variable resistor, and is used for changing the resistance value of the variable resistor according to the calculation result of the error calculation circuit, so as to adjust the input current of the control terminal of the corresponding transistor. 10. The control device according to claim 1, wherein the plurality of transistors are IGBTs. 11. The control device according to claim 10, wherein the plurality of transistors have substantially the same conduction characteristics. 12. The control device according to claim 10, wherein the transistor controller adjusts the input voltage of the control terminal of each transistor according to the calculation result of the error calculation circuit, so as to control the current of the first terminal of the transistor. 13. The control device according to claim 1, wherein the plurality of transistors comprise at least one BJT and at least one IGBT. 14. The control device according to claim 1, wherein the plurality of impedance elements have substantially the same impedance value. 15. The control device according to claim 1, wherein the plurality of series of LEDs comprises a first series corresponding to a first color and a second series corresponding to a second color. 16. The control device according to claim 1, wherein the plurality of transistors are all operated in an active region. 17. The control device according to claim 1, wherein the control terminal is a base, the first terminal is a collector, and the second terminal is an emitter. 18. A light source module, comprising: A plurality of light emitting diode strings each have a first end and a second end, wherein the first ends of the plurality of light emitting diode strings are all electrically connected to an operating voltage; A plurality of transistors all have a control terminal, a first terminal and a second terminal, wherein the first terminal of each transistor is electrically connected to the second terminal of a corresponding series in the plurality of light emitting diode series, and the The second terminals of the multiple transistors are respectively grounded through multiple impedance elements; an error calculation circuit, electrically connected to the second terminals of the plurality of transistors, and used to calculate the difference between the voltage of the second terminal of each transistor and the corresponding reference voltage; and The transistor controller is electrically connected to the error calculation circuit and the control terminals of the plurality of transistors, and is used for controlling the current of the first terminal of each transistor according to the calculation result of the error calculation circuit. 19. The light source module according to claim 18, wherein the plurality of transistors are bipolar transistors. 20. The light source module according to claim 19, wherein the transistor controller adjusts the input current of the control terminal of each transistor according to the calculation result of the error calculation circuit, so as to control the current of the first terminal of the transistor. 21. The light source module according to claim 19, wherein the plurality of transistors have substantially the same common emitter current gain. 22. The light source module according to claim 18, wherein the plurality of transistors are IGBTs. 23. The light source module according to claim 22, wherein the transistor controller adjusts the input voltage of the control terminal of each transistor according to the calculation result of the error calculation circuit, so as to control the current of the first terminal of the transistor. 24. The light source module according to claim 18, wherein the plurality of LED strings correspond to the same color. 25. The light source module according to claim 18, wherein the plurality of transistors are all operated in an active region. 26. The light source module according to claim 18, wherein the control terminal is a base, the first terminal is a collector, and the second terminal is an emitter.

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