CN204362375U - LED drive circuit - Google Patents

Abstract

The utility model discloses an LED driving circuit, which comprises an LED group circuit, an error amplifier circuit, a power supply voltage control circuit, a reference voltage source and a closed-loop connection circuit; the power supply voltage control circuit is connected to the LED group circuit; The voltage signal input terminal is connected to the LED group circuit; the second voltage signal input terminal of the error amplifier circuit is connected to the reference voltage source; the signal output terminal of the error amplifier circuit is connected to the power supply voltage control circuit; the closed-loop connection circuit is connected to the power supply voltage control circuit The output terminal of the circuit is connected with the first voltage signal input terminal of the error amplification circuit. Implementing the utility model can realize LED constant current control and prevent voltage overshoot phenomenon when the power supply is started, protect the LED, and ensure low hardware cost at the same time.

Description

A kind of LED driving circuit

technical field

The utility model relates to the technical field of LEDs, in particular to an LED driving circuit. the

Background technique

LED, or light-emitting diode, has nonlinear volt-ampere characteristics and a negative temperature coefficient. Due to the nonlinear volt-ampere characteristics, if the constant voltage source is used for driving, then when the constant voltage source is not stable enough, fluctuations will occur, which will cause large current changes in the LED, resulting in unstable luminance of the LED, and even burning the LED. Due to the negative temperature coefficient, if driven by a constant voltage source, when the temperature increases, its current will increase, but its brightness will not increase. An increase in current will only increase its temperature rise, which will increase light decay and reduce lifespan. Similarly, if driven by a constant voltage source, when the temperature drops, its current will drop, resulting in a drop in luminous brightness. Therefore, LED drivers generally use constant current sources.

The constant current drive is to adjust the size of the power supply voltage by collecting the sampling voltage of the LED to form a closed loop, so that the current passing through the LED is stable. However, since the LED itself has a turn-on voltage, when the power supply voltage is just started, it is not enough to make the LED turn on, so the sampling voltage output of the LED is zero, causing the LED drive circuit to open the loop. Therefore, the rapid rise of the power supply voltage is not controlled, and the phenomenon of output overshoot occurs, which may cause the LED to burn out in severe cases.

Utility model content

The purpose of the utility model is to overcome the deficiencies of the prior art and provide an LED driving circuit, which can realize LED constant current control and prevent voltage overshoot when the power supply is started, so as to protect the LED.

In order to achieve the above object, the utility model embodiment adopts the following technical solutions:

An LED driving circuit, comprising an LED group circuit, an error amplifier circuit, a power supply voltage control circuit, a reference voltage source, a first resistor, a second resistor, and a first capacitor;

The output terminal of the power supply voltage control circuit is connected to the power supply terminal of the LED group circuit;

The first voltage signal input end of the error amplifier circuit is connected to the signal acquisition end of the LED group circuit; the second voltage signal input end of the error amplifier circuit is connected to the reference voltage source; the error amplifier circuit The signal output terminal is connected to the input terminal of the power supply voltage control circuit;

The closed-loop connection circuit connects the output end of the power supply voltage control circuit with the first voltage signal input end of the error amplifier circuit.

Further, the closed-loop connection circuit includes a first resistor, a second resistor and a first capacitor;

The first end of the first resistor is connected to the output end of the power supply voltage control circuit;

The first end of the second resistor is connected to the second end of the first resistor, and the second end of the second resistor is grounded;

The first end of the first capacitor is connected to the second end of the first resistor, and the second end of the first capacitor is connected to the first voltage signal input end of the error amplifier circuit.

Further, the LED group circuit includes N LED lamps and sampling resistors connected in series in sequence, N≥1; wherein, the anode of the first LED lamp is the power supply terminal of the LED group circuit; the negative electrode of the Nth LED lamp is It is connected with the first end of the sampling resistor, and the second end of the sampling resistor is grounded; the first end of the sampling resistor is the signal collecting end of the LED group circuit.

Further, the error amplifier circuit includes an operational amplifier, a third resistor, a second capacitor, and a third capacitor; the non-inverting input terminal of the operational amplifier is the second voltage signal input terminal of the error amplifier circuit, and the operational The inverting input end of the amplifier is the first voltage signal input end of the error amplifier circuit, the output end of the operational amplifier is the signal output end of the error amplifier circuit; the first end of the third resistor is connected to the The output end of the operational amplifier, the second end of the third resistor is connected to the first end of the second capacitor; the second end of the second capacitor is connected to the inverting input end of the operational amplifier; the third The first terminal of the capacitor is connected to the output terminal of the operational amplifier, and the second terminal of the third capacitor is connected to the inverting input terminal of the operational amplifier.

Further, the LED driving circuit further includes a voltage divider circuit; the reference voltage source is connected to the second voltage signal input terminal of the error amplifier circuit through the voltage divider circuit.

Further, the voltage dividing circuit includes a fourth resistor, a fifth resistor and a fourth capacitor; the first end of the fourth resistor is connected to the reference voltage source, and the second end of the fourth resistor is connected to the first The first end of five resistors; the first end of the fifth resistor is connected to the second voltage signal input end of the error amplifier circuit, and the second end of the fifth resistor is grounded; the fourth capacitor and the first Five resistors are connected in parallel.

Further, the LED drive circuit further includes an RC filter circuit; the signal acquisition terminal of the LED group circuit is connected to the first voltage signal input terminal of the error amplifier circuit through the RC filter circuit.

Further, the RC filter circuit includes a sixth resistor and a fifth capacitor; the first end of the sixth resistor is connected to the signal collection end of the LED group circuit, and the second end of the sixth resistor is connected to the first The first end of the five capacitors; the second end of the fifth capacitor is grounded; the second end of the sixth resistor is connected to the first voltage signal input end of the error amplifier circuit.

Further, the LED drive circuit further includes an optocoupler isolation circuit; the signal output terminal of the error amplifier circuit is connected to the input terminal of the power supply voltage control circuit through the optocoupler isolation circuit.

Further, the first resistor is a single resistor or a resistor network composed of multiple resistors connected in parallel or in series; the second resistor is a single resistor or a resistor network composed of multiple resistors connected in parallel or in series formed resistor network. .

Compared with the prior art, the beneficial effect of the LED driving circuit provided by the embodiment of the present invention is that the output end of the power supply voltage control circuit is connected with the first voltage signal input of the error amplifier circuit through a closed-loop connection circuit. When the power supply starts, it forms a temporary closed loop, so that the output voltage Vout of the power supply can rise steadily and prevent the output from overshooting. When the power supply output voltage Vout is in a steady state, the first resistor R1 and the second resistor R2 in the closed-loop connection circuit divide the voltage, so that the first capacitor C1 can withstand a higher voltage, for example, a chip with a lower withstand voltage can be used Capacitors have lower cost and occupy a small PCB area, which has advantages in layout. At the same time, in the steady state, RB346 and RB365 are used as output dummy loads, no need to add dummy loads, and the device utilization is optimized. It can realize the LED constant current control and prevent the voltage overshoot phenomenon when the power supply is started, protect the LED, and at the same time ensure low hardware cost.

Description of drawings

Fig. 1 is the structural block diagram of a kind of LED driving circuit of the utility model embodiment;

Fig. 2 is the circuit diagram of the closed-loop connection circuit 5 in Fig. 1;

Fig. 3 is a structural block diagram of an LED drive circuit according to another embodiment of the present invention;

FIG. 4 is a circuit diagram of an LED driving circuit in FIG. 3 .

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention.

Please refer to Figure 1, which is a functional block diagram of an LED driving circuit provided by an embodiment of the present invention, including an LED group circuit 1, an error amplifier circuit 2, a power supply voltage control circuit 3, a reference voltage source 4, and a closed-loop connection circuit 5;

The output terminal of the power supply voltage control circuit 3 is connected to the power supply terminal of the LED group circuit 1;

The first voltage signal input end of the error amplifier circuit 2 is connected to the signal acquisition end of the LED group circuit 1; the second voltage signal input end of the error amplifier circuit 2 is connected to the reference voltage source 4; the The signal output end of the error amplification circuit 2 is connected with the input end of the power supply voltage control circuit 3;

The closed-loop connection circuit 5 connects the output terminal of the power supply voltage control circuit 3 and the first voltage signal input terminal of the error amplifier circuit 2 .

Specifically, the closed-loop connection circuit 5 includes a first resistor R1, a second resistor R2 and a first capacitor C1.

As shown in FIG. 2 , it is a circuit diagram of the closed-loop connection circuit 5 in FIG. 1 .

The first end of the first resistor R1 is connected to the output end of the power supply voltage control circuit 3;

The first end of the second resistor R2 is connected to the second end of the first resistor R1, and the second end of the second resistor R2 is grounded;

The first terminal of the first capacitor C1 is connected to the second terminal of the first resistor R1 , and the second terminal of the first capacitor C1 is connected to the first voltage signal input terminal of the error amplifier circuit 2 .

Wherein, the first resistor R1 is a single resistor or a resistor network composed of multiple resistors connected in parallel or in series; the second resistor R2 is a single resistor or a resistor network composed of multiple resistors connected in parallel or in series Resistive network formed by way. The first capacitor C1 plays a role of "DC blocking" when the output voltage Vout of the power supply is stable.

The working principle of an LED driving current provided in this embodiment is as follows: when the output voltage Vout of the power supply rises from 0 and the LED group is not turned on, the output voltage Vout of the power supply passes through the first circuit in the closed-loop connection circuit 5 The resistor R1 and the first capacitor C1 are input to the first voltage signal input end of the error amplifier circuit 2; the error amplifier circuit 2 outputs a control signal after comparing the output voltage Vout of the power supply with the reference voltage to control the output of the power supply Voltage Vout, so there will be no overshoot phenomenon during the rising phase of Vout. When the power supply output voltage Vout is in a steady state, the LED group is turned on, the error amplifier circuit collects the voltage signal of the LED group, compares it with the reference voltage, and outputs a control signal after comparison to control the power supply output voltage Vout, thus Can control LED group constant current.

Compared with the prior art, the closed-loop connection circuit in the embodiment of the utility model connects the output terminal of the power supply voltage control circuit and the first voltage signal input terminal of the error amplifier circuit, and forms a temporary closed loop when the power supply is started. circuit, so that the output voltage Vout of the power supply can rise steadily and prevent output overshoot; when the output voltage Vout of the power supply is in a steady state, the first resistor R1 and the second resistor R2 divide the voltage, so that the first capacitor C1 can withstand a higher voltage. For example, a 50V withstand voltage chip capacitor can be used, which has a lower cost and occupies a small PCB area, which has advantages in layout. At the same time, in the steady state, RB346 and RB365 are used as output dummy loads, no need to add dummy loads, and the device utilization is optimized.

As shown in FIG. 3 , it is a structural block diagram of an LED driving circuit according to another embodiment of the present invention. The LED drive circuit provided by another embodiment of the utility model includes the LED group circuit 1, the error amplifier circuit 2, the power supply voltage control circuit 3, the reference voltage source 4 and the closed-loop connection circuit 5 in the previous embodiment. In addition, It includes a voltage divider circuit 6 and an RC filter circuit 7 . The reference voltage source 4 is connected to the second voltage signal input end of the error amplifier circuit 2 through the voltage divider circuit 6 . The signal acquisition end of the LED group circuit 1 is connected to the first voltage signal input end of the error amplifier circuit 2 through the RC filter circuit 7 .

Please refer to FIG. 4 , which is a circuit diagram of an LED driving circuit in FIG. 3 . Wherein, Vout is the output voltage of the power supply voltage control circuit 3 (not shown in FIG. 4 ), V0 is the reference voltage, and V1 is the output voltage of the error amplifier circuit 2 .

The LED group circuit 1 includes N LED lamps connected in series and a sampling resistor Rs, N≥1; wherein, the anode of the first LED lamp is the power supply terminal of the LED group circuit 1; the negative electrode of the Nth LED lamp is It is connected with the first end of the sampling resistor Rs, and the second end of the sampling resistor Rs is grounded; the first end of the sampling resistor Rs is the signal collecting end of the LED group circuit 1 . In this embodiment, N=3, and the LED group circuit 1 includes D1 , D2 , D3 and the sampling resistor Rs in FIG. 4 . The function of the sampling resistor Rs is to convert the current signal flowing through the LED group circuit 1 into a voltage signal for processing by the error amplifier circuit 2 .

The error amplifier circuit 2 includes an operational amplifier A1, a third resistor R3, a second capacitor C2 and a third capacitor C3. The non-inverting input terminal of the operational amplifier A1 is the second voltage signal input terminal of the error amplifier circuit 2, and the inverting input terminal of the operational amplifier A1 is the first voltage signal input terminal of the error amplifier circuit 2, The output end of the operational amplifier A1 is the signal output end of the error amplifier circuit 2; the first end of the third resistor R3 is connected to the output end of the operational amplifier A1, and the second end of the third resistor R3 Connect the first terminal of the second capacitor C2; the second terminal of the second capacitor C2 is connected to the inverting input terminal of the operational amplifier A1; the first terminal of the third capacitor C3 is connected to the operational amplifier A1 The output terminal of the third capacitor C3 is connected to the inverting input terminal of the operational amplifier A1. The operational amplifier A1, the third resistor R3, the second capacitor C2 and the third capacitor C3 form a negative feedback amplifier circuit.

The voltage divider circuit 6 includes a fourth resistor R4, a fifth resistor R5, and a fourth capacitor C4; the first end of the fourth resistor R4 is connected to the reference voltage source 4, and the second end of the fourth resistor R4 Connect the first end of the fifth resistor R5; the first end of the fifth resistor R5 is connected to the second voltage signal input end of the error amplifier circuit 2, and the second end of the fifth resistor R5 is grounded; The fourth capacitor C4 is connected in parallel with the fifth resistor R5. The reference voltage source 4 can provide a lower (lower than 1V) reference voltage for the error amplifier circuit 2 after being divided by the voltage divider circuit 6; by adjusting the fourth resistor R4 and the fifth The ratio of resistor R5 can output different reference voltages. The fourth capacitor C4 is used to filter high frequency components in the reference voltage source 4 .

The RC filter circuit 7 includes a sixth resistor R6 and a fifth capacitor C5; the first end of the sixth resistor R6 is connected to the signal collection end of the LED group circuit 1, and the second end of the sixth resistor R6 is connected to The first end of the fifth capacitor C5; the second end of the fifth capacitor C5 is grounded; the second end of the sixth resistor R6 is connected to the first voltage signal input end of the error amplifier circuit 2 . The sixth resistor R6 acts as a current limiter in the circuit, and the fifth capacitor C5 acts as a smoothing filter; the amplitude-frequency of the circuit can be improved by adjusting the sixth resistor R6 and the fifth capacitor C5 characteristics and phase-frequency characteristics.

As a further improvement of this embodiment, the LED drive circuit may also include an optocoupler isolation circuit; the signal output end of the error amplifier circuit 2 is connected to the input end of the power supply voltage control circuit 3 through the optocoupler isolation circuit . The optocoupler isolation circuit can isolate the power supply voltage control circuit 3 from the error amplifier circuit 2 to prevent the strong current in the error amplifier circuit 2 from interfering with the weak current signal in the power supply voltage control circuit 3 .

It should be noted that another embodiment of the utility model is just a better embodiment, but the voltage divider circuit 6, RC filter circuit 7 and optocoupler isolation circuit are not necessary, that is, in the previous embodiment The LED driving circuit can also realize the basic purpose of the utility model.

The beneficial effect of the LED driving circuit provided by the embodiment of the present invention is that: the output end of the power supply voltage control circuit and the first voltage signal input end of the error amplifier circuit are connected through a closed-loop connection circuit. When the power supply is started, A temporary closed loop is formed so that the output voltage Vout of the power supply can rise steadily and prevent output overshoot. When the output voltage Vout of the power supply is in a steady state, the first resistor R1 and the second resistor R2 divide the voltage so that the first capacitor C1 can withstand a higher voltage. For example, a chip capacitor with a lower withstand voltage value can be used, and the cost is lower. , and occupies a small PCB area, which has advantages in layout. At the same time, in the steady state, RB346 and RB365 are used as output dummy loads, no need to add dummy loads, and the device utilization is optimized. It can realize LED constant current control and prevent voltage overshoot when the power supply is started, protect LED, and the cost of hardware is relatively low.

The above are only preferred implementations of the present utility model, and it should be noted that the above preferred implementations should not be regarded as limitations on the present utility model. The protection scope of the present utility model should be determined by the scope defined in the claims. For those skilled in the art, without departing from the spirit and scope of the utility model, some improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the utility model.

Claims (10)

1. a LED drive circuit, is characterized in that: comprise LED group circuit, error amplifying circuit, source voltage control circuit, reference voltage source and closed loop connecting circuit;

The output of described source voltage control circuit connects the power end of described LED group circuit;

First voltage signal inputs of described error amplifying circuit is connected with the signals collecting end of described LED group circuit; Second voltage signal inputs of described error amplifying circuit is connected with described reference voltage source; The signal output part of described error amplifying circuit is connected with the input of described source voltage control circuit;

Described closed loop connecting circuit connects the output of described source voltage control circuit and the first voltage signal inputs of described error amplifying circuit.

2. a kind of LED drive circuit as claimed in claim 1, is characterized in that:

Described closed loop connecting circuit comprises the first resistance, the second resistance and the first electric capacity;

The first end of described first resistance connects the output of described source voltage control circuit;

The first end of described second resistance connects the second end of described first resistance, and the second end ground connection of described second resistance;

The first end of described first electric capacity connects the second end of described first resistance, and the second end of described first electric capacity connects the first voltage signal inputs of described error amplifying circuit.

3. a kind of LED drive circuit as claimed in claim 1, is characterized in that: described LED group circuit comprises N number of LED and sampling resistor of connecting successively, N >=1; Wherein, the power end of the just very described LED group circuit of first LED; The negative pole of N number of LED is connected with the first end of described sampling resistor, the second end ground connection of described sampling resistor; The first end of described sampling resistor is the signals collecting end of described LED group circuit.

4. a kind of LED drive circuit as claimed in claim 1, is characterized in that: described error amplifying circuit comprises operational amplifier, the 3rd resistance, the second electric capacity and the 3rd electric capacity; The normal phase input end of described operational amplifier is the second voltage signal inputs of described error amplifying circuit, the inverting input of described operational amplifier is the first voltage signal inputs of described error amplifying circuit, and the output of described operational amplifier is the signal output part of described error amplifying circuit; The first end of described 3rd resistance connects the output of described operational amplifier, and the second end of described 3rd resistance connects the first end of described second electric capacity; Second end of described second electric capacity connects the inverting input of described operational amplifier; The first end of described 3rd electric capacity connects the output of described operational amplifier, and the second end of described 3rd electric capacity connects the inverting input of described operational amplifier.

5. a kind of LED drive circuit as claimed in claim 1, is characterized in that: described LED drive circuit also comprises bleeder circuit; Described reference voltage source is connected to the second voltage signal inputs of described error amplifying circuit by described bleeder circuit.

6. a kind of LED drive circuit as claimed in claim 5, is characterized in that: described bleeder circuit comprises the 4th resistance, the 5th resistance and the 4th electric capacity; The first end of described 4th resistance connects described reference voltage source, and the second end of described 4th resistance connects the first end of described 5th resistance; The first end of described 5th resistance connects the second voltage signal inputs of described error amplifying circuit, the second end ground connection of described 5th resistance; Described 4th electric capacity and described 5th resistor coupled in parallel.

7. a kind of LED drive circuit as claimed in claim 1, is characterized in that: described LED drive circuit also comprises RC filter circuit; The signals collecting end of described LED group circuit is connected with the first voltage signal inputs of described error amplifying circuit by described RC filter circuit.

8. a kind of LED drive circuit as claimed in claim 7, is characterized in that: described RC filter circuit comprises the 6th resistance and the 5th electric capacity; The first end of described 6th resistance connects the signals collecting end of described LED group circuit, and the second end of described 6th resistance connects the first end of described 5th electric capacity; Second end ground connection of described 5th electric capacity; Second end of described 6th resistance connects the first voltage signal inputs of described error amplifying circuit.

9. a kind of LED drive circuit as claimed in claim 1, is characterized in that: described LED drive circuit also comprises optical coupling isolation circuit; The signal output part of described error amplifying circuit is connected with the input of described source voltage control circuit by described optical coupling isolation circuit.

10. a kind of LED drive circuit as claimed in claim 1, is characterized in that: the resistor network that described first resistance is single resistor or is made up of in mode that is in parallel or series connection multiple resistor; The resistor network that described second resistance is single resistor or is made up of in mode that is in parallel or series connection multiple resistor.