CN112637996B - LED driving circuit and control method - Google Patents

Abstract

The present invention proposes an LED driving circuit and a control method. The LED driving circuit includes a first regulating circuit and a second regulating circuit. The first regulating circuit is connected in series with the LED load to form a first series circuit. The first regulating circuit receives the first A reference voltage, the first reference voltage adjusts the LED load current through the first adjustment circuit; the second adjustment circuit is connected in series with the first capacitor to form a second series circuit, and the second series circuit and the first series circuit in parallel. When the input voltage is greater than the LED load voltage, the input voltage supplies power to the LED load; when the input voltage is lower than the LED load voltage, the second capacitor supplies power to the LED load. The invention effectively prevents the LED stroboscopic phenomenon caused by too low input voltage, reduces the volume of the electrolytic capacitor used as the first capacitor, and accelerates the LED voltage to quickly enter a steady state during the LED start-up process.

Description

LED driving circuit and control method

technical field

The invention relates to the field of power electronics, in particular to an LED driving circuit and a control method.

Background technique

The prior art linear LED driving circuit includes a regulating transistor M1, a filter capacitor C0 and a driving circuit for driving the regulating transistor. The driving circuit obtains a reference voltage through the dimming signal, and performs operational amplification on the reference voltage and the LED current sampling signal to adjust the LED current.

The prior art linear LED drive circuit is shown in FIG. 1 , a capacitor C0 is connected in parallel to both ends of the LED, and when the input voltage is lower than the LED load voltage, the capacitor C0 supplies power to the LED load. The disadvantage of this method is that when the capacitor C0 is small, the capacitor voltage may not be sufficient to provide the voltage required by the LED load during the discharge of the capacitor C0, resulting in flickering of the LED, and it is necessary to connect a large capacitor in parallel or increase the flicker removal The chip can reduce the stroboscopic degree, but at the same time, the cost is increased, which is not conducive to the integration of the circuit. Linear drive circuits are difficult to meet high-efficiency applications.

Contents of the invention

The object of the present invention is to provide an LED drive circuit and control method for suppressing LED current ripple, to solve the technical problem of LED flickering in the prior art, and also help to improve the start-up speed and power supply efficiency of the LED.

In order to achieve the above object, the present invention provides an LED drive circuit, the input voltage is obtained after the AC input is rectified, including:

The first regulating circuit is connected in series with the LED load to form a first series circuit, the first regulating circuit receives a first reference voltage, and the first reference voltage regulates the LED load current through the first regulating circuit;

A second regulating circuit, connected in series with the first capacitor to form a second series circuit, the second series circuit is connected in parallel with the first series circuit;

When the input voltage is greater than the LED load voltage, the input voltage supplies power to the LED load; when the input voltage is lower than the LED load voltage, the second capacitor supplies power to the LED load.

Optionally, the second adjustment circuit includes a second adjustment tube and a first control circuit, the second adjustment tube is connected in series with the first capacitor; the first control circuit is connected to the control terminal of the second adjustment tube connected, the first control circuit receives the first control signal and the second control signal, and by controlling the second adjusting tube, the second control signal approaches the first control signal, so that the first The valley value of the voltage across the capacitor is greater than the LED load voltage.

Optionally, the first control circuit includes a second operational amplifier and a second capacitor, and the two input terminals of the second operational amplifier respectively receive the first control signal representing the LED load voltage and the voltage representing the voltage across the first capacitor. The second control signal, the output end of which is connected to the second capacitor; the output end of the second operational amplifier is the first node, and the first node voltage or its converted value is used as the second reference signal for sampling The current flowing through the second adjustment transistor is used as the second sampling signal, which is compared with the second reference signal, so that the second sampling signal approaches the second reference signal.

Optionally, the first control circuit further includes a third operational amplifier, and two input terminals of the third operational amplifier respectively receive the second reference signal and the second sampling signal.

Optionally, the first control circuit further includes a reference conversion module, the reference conversion module receives the first node voltage and compensates it, so as to obtain a second reference signal.

Optionally, the second reference signal has a concave shape during half of the power frequency cycle.

Optionally, the reference conversion module makes a difference between the first node voltage and a compensation parameter to obtain a second reference signal, and the compensation parameter has the same variation trend as the input voltage.

Optionally, the LED driving circuit is characterized in that: the compensation parameter represents the difference between the input voltage and the LED load voltage.

Optionally, the second regulating circuit further includes a first diode, and the first diode and the second regulating transistor are connected in antiparallel.

Optionally, the first adjustment circuit includes a first adjustment transistor and a first operational amplifier, the first adjustment transistor is connected in series with the LED load, and the output terminal of the first operational amplifier is connected to the first adjustment transistor The two input terminals of the first operational amplifier respectively receive the first reference voltage and the first sampling signal representing the LED load current, so that the first sampling signal approaches the first reference voltage. The first reference voltage adjusts the LED load current by adjusting the first adjustment transistor.

The present invention also provides an LED control method. Based on the LED control circuit, the LED drive circuit includes a first regulating circuit and a second regulating circuit, and is characterized in that: the first regulating circuit is connected in series with the LED load to form a first series circuit, The first adjustment circuit receives a first reference voltage, and the first reference voltage adjusts the LED load current through the first adjustment circuit; the second adjustment circuit is connected in series with the first capacitor to form a second series circuit, and the second A series circuit and the first series circuit; when the input voltage is greater than the LED load voltage, the input voltage supplies power to the LED load; when the input voltage is less than the LED load voltage, the second regulating circuit supplies power to the LED load LED load power supply.

Compared with the prior art, the present invention has the following advantages: adopting the present invention, when the input voltage is lower than the LED load voltage, the valley value of the voltage across the first capacitor is greater than the LED load voltage, and the second capacitor has an effect on the LED load voltage. The above LED load power supply. The present invention effectively prevents the LED stroboscopic phenomenon caused by too low input voltage, reduces the volume of the electrolytic capacitor used as the first capacitor, and at the same time accelerates the establishment of the voltage of the electrolytic capacitor during the LED start-up process to help the LED voltage enter quickly steady state.

Description of drawings

Fig. 1 is the schematic diagram of the prior art LED control circuit;

Fig. 2 is a schematic diagram of the LED control circuit of the present invention;

Fig. 3 is a schematic diagram of the first regulating circuit of the present invention;

Fig. 4 is the schematic diagram of the second regulation circuit of the present invention;

Fig. 5 is a waveform diagram of the LED control circuit of the present invention;

Detailed ways

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any alternatives, modifications, equivalent methods and schemes made within the spirit and scope of the present invention.

In order to provide the public with a thorough understanding of the present invention, specific details are set forth in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details.

In the following paragraphs the invention is described more specifically by way of example with reference to the accompanying drawings. It should be noted that all the drawings are in a relatively simplified form and use inaccurate scales to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention.

Fig. 2 schematically shows the schematic diagram of the LED driving circuit of the present invention, the AC input is rectified to obtain the input voltage VIN, the LED load conduction voltage is VLED, and the LED driving circuit includes a first regulating circuit U1 and a second regulating circuit U2, the second A regulating circuit and the LED load are connected in series to form a first series circuit, a second regulating circuit and the first capacitor C1 are connected in series to form a second series circuit, and the first series circuit and the second series circuit are connected in parallel. When VIN>VLED, the input voltage VIN supplies power to the LED load; when VIN<VLED, the first capacitor C1 supplies power to the LED load.

Fig. 3 shows the schematic diagram of the first regulation circuit of the present invention, including the first regulation transistor M1 and the first operational amplifier U11, the first regulation transistor M1 is connected in series with the LED load, and the output terminal of the first operational amplifier U11 is connected to the first operational amplifier U11. The control terminal of an adjustment transistor M1 is connected, and the two input terminals of the first operational amplifier U11 respectively receive the first reference voltage VREF1 and the first sampling signal VCS1 representing the LED load current, so that the first sampling signal VCS1 approaches the first A reference voltage VREF1, that is, to keep the current flowing through the first adjustment transistor M1 relatively constant, and the first reference voltage VREF1 adjusts the LED load current by adjusting the first adjustment transistor M1. Of course, a dimming control circuit may also be provided to control the first reference voltage VREF1 so as to control and change the current flowing through the first adjustment tube M1.

Fig. 4 illustrates the schematic diagram of the second adjustment circuit of the present invention, including the second adjustment tube M2 and the first control circuit, the second adjustment tube M2 is connected in series with the first capacitor C1, the first control circuit and the control terminal of the second adjustment tube M2 connected to adjust the voltage across the first capacitor C1 to keep it stable. The first control circuit includes a second operational amplifier U12 and a second capacitor C2. The two input terminals of the second operational amplifier U12 respectively receive the first control signal VLED' representing the LED load voltage and the second control signal VLED' representing the voltage across the first capacitor. For the control signal VCAP', the output end of the second operational amplifier U12 is connected to the second capacitor C2. By controlling the second adjustment transistor M2, the second control signal VCAP' approaches the first control signal VLED', so that the voltage across the first capacitor C1 approaches the LED load voltage. The output terminal of the second operational amplifier U11 is the first node, and the voltage VCOMP of the first node or the converted value thereof is used as the second reference signal VREF2. Sampling the current flowing through the second adjustment transistor M2 as the second sampling signal VCS2, connecting it to the first input terminal of the third operational amplifier U13, and connecting the second reference signal VREF2 to the second input terminal of the third operational amplifier U13, so that The second sampling signal VCS2 approaches the second reference signal VREF2. According to the comparison result between the non-inverting input terminal and the inverting input terminal of the third operational amplifier U13, the control terminal of the second adjustment transistor is pulled up or pulled down, and then the charging current of the first capacitor is controlled to control the voltage across the first capacitor.

Further, in order to realize efficient functions, the first control circuit further includes a reference conversion module, which receives the difference between the first node voltage VCOMP and the compensation parameter to obtain the second sampling signal VREF2, and the compensation parameter and the input voltage change The trend is the same. In order to improve the quick start-up capability on the basis of efficient control, the compensation coefficient is set according to the following rule: the compensation parameter represents the difference between the input voltage VIN and the LED load voltage VLED.

The second regulating circuit further includes a first diode D1, and the first diode and the second regulating transistor M2 are connected in antiparallel.

On the basis of the circuit in Fig. 4, Fig. 5 illustrates the working waveform diagram of the LED drive circuit of the present invention, wherein IC1 corresponds to the charge and discharge current waveform of the first capacitor C1 in Fig. 2, ILED is the LED current waveform, and IOUT is the output current waveform of the rectifier circuit, The concave current makes the circuit of the present invention exhibit high efficiency performance.

Based on the above LED driving circuit, a corresponding LED control method can be obtained. The LED driving circuit includes a first regulating circuit and a second regulating circuit, and is characterized in that: the first regulating circuit is connected in series with the LED load to form a first series circuit, so The first regulating circuit receives a first reference voltage, and the first reference voltage regulates the LED load current through the first regulating circuit; the second regulating circuit is connected in series with the first capacitor to form a second series circuit, and the second series circuit The circuit is connected in parallel with the first series circuit; when the input voltage is greater than the LED load voltage, the input voltage supplies power to the LED load; when the input voltage is lower than the LED load voltage, the second regulation circuit supplies power to the LED load power supply.

In addition, the technical features of the LED driving circuit of the present invention can be used in the LED control method of the present invention.

The implementation methods described above do not constitute a limitation to the scope of protection of the technical solution. Any modifications, equivalent replacements and improvements made within the spirit and principles of the above implementation methods shall be included in the protection scope of the technical solution.

Claims (9)

1. An LED driving circuit, in which an ac input is rectified to obtain an input voltage, comprising:

the first regulating circuit is connected with the LED load in series to form a first series circuit, and the first regulating circuit receives a first reference voltage, and the first reference voltage regulates the current of the LED load through the first regulating circuit;

the second regulating circuit is connected with the first capacitor in series to form a second series circuit, and the second series circuit is connected with the first series circuit in parallel;

when the input voltage is larger than the LED load voltage, the input voltage supplies power to the LED load; when the input voltage is smaller than the LED load voltage, the first capacitor supplies power to the LED load;

the second adjusting circuit comprises a second adjusting tube and a first control circuit, and the second adjusting tube is connected in series with the first capacitor; the first control circuit is connected with the control end of the second adjusting tube, receives a first control signal and a second control signal, and enables the second control signal to approach to the first control signal and enables the voltage valley value at the two ends of the first capacitor to be larger than the LED load voltage by controlling the second adjusting tube;

the first control circuit comprises a second operational amplifier and a second capacitor, wherein two input ends of the second operational amplifier respectively receive a first control signal representing the load voltage of the LED and a second control signal representing the voltage at two ends of the first capacitor, and the output end of the second operational amplifier is connected with the second capacitor; the output end of the second operational amplifier is a first node, the voltage of the first node or the converted value is used as a second reference signal, the current flowing through the second adjusting tube is sampled to be used as a second sampling signal, and the second sampling signal is compared with the second reference signal, so that the second sampling signal approaches to the second reference signal.

2. The LED driving circuit according to claim 1, wherein: the first control circuit further comprises a third operational amplifier, two input ends of the third operational amplifier respectively receive the second reference signal and the second sampling signal, and an output end of the third operational amplifier is connected with a control end of the second adjusting tube.

3. The LED driving circuit according to claim 1, wherein: the first control circuit further includes a reference conversion module that receives and compensates for the first node voltage to obtain a second reference signal.

4. The LED driving circuit according to claim 3, wherein: the second reference signal is concave in a half power frequency period.

5. The LED driving circuit of claim 4, wherein: the reference conversion module is used for obtaining a second reference signal by making a difference between the first node voltage and a compensation parameter, wherein the compensation parameter is the same as the variation trend of the input voltage.

6. The LED driving circuit of claim 5, wherein: the compensation parameter characterizes a difference between an input voltage and an LED load voltage.

7. The LED driving circuit according to claim 2, wherein: the second regulating circuit further comprises a first diode, and the first diode and the second regulating tube are connected in anti-parallel.

8. A LED driving circuit according to any one of claims 1-3, characterized in that: the first adjusting circuit comprises a first adjusting tube and a first operational amplifier, the first adjusting tube is connected with the LED load in series, the output end of the first operational amplifier is connected with the control end of the first adjusting tube, and the two input ends of the first operational amplifier respectively receive a first reference voltage and a first sampling signal representing the LED load current, so that the first sampling signal approaches to the first reference voltage, and the first reference voltage adjusts the LED load current through adjusting the first adjusting tube.

9. An LED control method based on the LED driving circuit of any one of claims 1-8, the LED driving circuit comprising a first regulation circuit and a second regulation circuit, characterized in that: the first regulating circuit is connected with the LED load in series to form a first series circuit, and the first regulating circuit receives a first reference voltage, and the first reference voltage regulates the current of the LED load through the first regulating circuit; the second regulating circuit is connected with the first capacitor in series to form a second series circuit, and the second series circuit is connected with the first series circuit in parallel; when the input voltage is larger than the LED load voltage, the input voltage supplies power to the LED load; the second regulation circuit supplies power to the LED load when the input voltage is less than the LED load voltage.

Images