CN103763825B - LED constant current PWM drive circuit and three-primary color LED mixed light drive circuit - Google Patents

Abstract

The invention provides an LED constant-current PWM drive circuit and a three-primary-color LED mixed-light drive circuit. The LED constant current PWM drive circuit includes: a three-terminal bidirectional switch circuit, connected to an AC power supply, for converting a sinusoidal AC signal provided by the AC power supply into a sinusoidal chopping waveform signal; a PWM waveform signal generation circuit, connected to the three-terminal A bidirectional switch circuit is connected to generate a PWM waveform signal by using the sine chopping waveform signal; an LED constant current drive circuit is connected to the PWM waveform signal generating circuit and is used to control the LED light source by using the PWM waveform signal Turning on and off, so as to realize the constant current PWM driving of the LED. In the present invention, the three-terminal bidirectional switch circuit directly drives a resistive load instead of a capacitive load, so the technical solution can ensure a high power factor without affecting the quality of the entire power grid.

Description

LED constant current PWM drive circuit and tricolor LED mixed light drive circuit

technical field

The invention relates to the technical field of LEDs, in particular to an LED constant-current PWM drive circuit and a three-primary-color LED mixed-light drive circuit.

Background technique

Light Emitting Diode (LED for short) has become one of the most potential substitutes for traditional light sources due to its advantages of small size, energy saving, environmental protection, and long service life.

There are many ways to produce LED white light sources. One is to use blue LEDs to excite yellow phosphors to produce white light. However, the light output of white LEDs produced by this method is relatively random, and due to the aging of phosphors, the efficiency of LEDs will decrease. will decrease. The three-primary-color mixed light is a better white light generation method. The three-primary color mixing is to use red LED, blue LED and green LED to mix light. According to the CIE (International Commission on Illumination) chromaticity diagram, the ratio of the color temperature of light to the three primary colors r(λ), g(λ) and b(λ) is related, and satisfies the condition r(λ)+g(λ)+b(λ)=1, therefore, the three-primary-color mixed light can not only change the pulse width of the LED current to achieve brightness adjustment, but also can adjust the brightness according to the user's preference Change the ratio of lumens of the three primary colors to adjust the color temperature of the LED. At present, the commonly used dimming technologies of LEDs include PWM dimming and analog dimming. The dimming principle of the former is to control the conduction time of the current flowing through the LED, and the dimming principle of the latter is to directly control the magnitude of the current flowing through the LED.

A three-terminal bidirectional switch (TRIAC, bidirectional thyristor) is a commonly used rectifier device in the field of power electronics, and its conduction in two directions can be realized through the control signal of the gate. When the TRIAC is turned on, the gate control signal loses its control effect, and when the current passing through the TRIAC is lower than the holding current, the TRIAC turns from on to off. TRIAC-based dimmers are currently widely used in dimming applications for purely resistive loads such as incandescent lamps and halogen lamps. Load) voltage regulation, so as to achieve the purpose of dimming.

For LED lighting fixtures with capacitive loads, TRIAC dimmers will bring five major adverse effects, so strictly speaking, this is not a high-quality dimming technology. The first major adverse effect is that TRIAC dimming will inevitably destroy the power factor, because it uses a chopping method for dimming, especially when deep dimming, the power factor will become very low, and then affect the quality of the entire power grid; The second major adverse effect is that TRIAC dimming will produce serious EMI interference, because when the load is capacitive, the thyristor will be turned on and off to generate a strong surge on the output current waveform, and this surge current will cause serious EMI interference; the third major adverse effect is that TRIAC dimming will cause the power conversion efficiency of the entire lamp to be low, and when deep dimming is performed, the efficiency will be lower than 20%; the fourth major adverse effect is the TRIAC dimmer and LED lighting fixtures It is not matched, and this will easily cause the problem of output light flicker, affect the consumer experience, and even cause health problems; the fifth major adverse effect is that TRIAC dimmers will cause serious THD (Total Harmonic Distortion) problems , while international energy standards such as current harmonic standards compatibility test EN61000-3-2 began to require strict THD specifications.

Contents of the invention

(1) Technical problems to be solved

In view of the above technical problems, the present invention provides an LED constant-current PWM drive circuit and a three-primary-color LED mixed light drive circuit to improve the existing LED TRIAC dimming scheme and overcome the above five major problems.

(2) Technical solution

According to one aspect of the present invention, an LED constant current PWM driving circuit is provided. The LED constant current PWM drive circuit includes: a three-terminal bidirectional switch circuit, connected to an AC power supply, used to convert the sinusoidal AC signal provided by the AC power supply into a sinusoidal chopping waveform signal; a PWM waveform signal generation circuit, connected to the three-terminal bidirectional switch The circuit is connected to generate a PWM waveform signal by using the sine chopping waveform signal; the LED constant current drive circuit is connected to the PWM waveform signal generating circuit and used to control the on and off of the LED light source by using the PWM waveform signal, thereby realizing LED constant current PWM drive.

According to another aspect of the present invention, a three-primary-color LED mixed light driving circuit is also provided. The three-primary-color LED mixed-light driving circuit includes: a first LED constant-current PWM driving circuit, a second LED constant-current PWM driving circuit and a third LED constant-current PWM driving circuit; wherein, the three LED constant-current PWM driving circuits are all The LED constant current PWM driving circuit described above drives the red LED light source, the blue LED light source and the green LED light source respectively.

(3) Beneficial effects

It can be seen from the above technical solutions that the LED constant-current PWM drive circuit and the three-primary-color LED mixed-light drive circuit of the present invention have the following beneficial effects:

(1) The three-terminal bidirectional switch (TRIAC) circuit directly drives the load as a resistive load, not a capacitive load, so this technical solution can ensure a high power factor and will not affect the quality of the entire power grid;

(2) The three-terminal bidirectional switch (TRIAC) circuit directly drives the load as a resistor, so this technical solution will not generate strong surges on the output waveform, and then will not cause serious EMI interference;

(3) The three-terminal bidirectional switch (TRIAC) circuit directly drives the load as a resistor, and the power conversion efficiency is mainly determined by the efficiency of the LED constant current PWM drive circuit. Obviously, the efficiency of the LED constant current PWM drive circuit in this technical solution is higher than that of the traditional TRIAC. High dimming;

(4) Adopt constant current drive and PWM regulation, high compatibility with LED lamps;

(5) Since the three-terminal bidirectional switch (TRIAC) circuit in this technical solution is linear, it is regulated by PWM, and there is no harmonic generation, so the problem of THD will not occur.

Description of drawings

1 is a schematic structural diagram of an LED constant current PWM drive circuit according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a three-terminal bidirectional switch circuit in the LED constant current PWM drive circuit shown in FIG. 1;

FIG. 3 is a schematic structural diagram of a PWM waveform signal generating circuit in the LED constant current PWM drive circuit shown in FIG. 1;

4 is a schematic structural diagram of the LED constant current drive circuit in the LED constant current PWM drive circuit shown in FIG. 1;

Fig. 5 is a waveform signal diagram of some nodes in the LED constant current PWM driving circuit shown in Fig. 1;

FIG. 6 is a schematic structural diagram of a three-primary-color LED mixed light driving circuit according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be noted that, in the drawings or descriptions of the specification, similar or identical parts all use the same figure numbers. Implementations not shown or described in the accompanying drawings are forms known to those of ordinary skill in the art. Additionally, while illustrations of parameters including particular values may be provided herein, it should be understood that the parameters need not be exactly equal to the corresponding values, but rather may approximate the corresponding values within acceptable error margins or design constraints.

The invention provides an LED constant-current PWM driving circuit and a three-primary-color LED mixed-light driving circuit based on the LED constant-current PWM driving circuit. The LED constant current drive circuit includes a temperature negative feedback circuit, so that the LED will automatically reduce the operating current when the temperature is too high to prevent the temperature from rising further, ensuring the high efficiency and long life of the LED.

In the first exemplary embodiment of the present invention, an LED constant current PWM driving circuit is provided. FIG. 1 is a schematic structural diagram of an LED constant current PWM driving circuit according to a first embodiment of the present invention. Please refer to Figure 1, the LED constant current PWM drive circuit in this embodiment includes:

A three-terminal bidirectional switch (TRIAC) circuit, connected to an AC power source, is used to convert the sinusoidal AC signal provided by the AC power source into a sinusoidal chopping waveform signal;

A PWM waveform signal generation circuit, connected to a three-terminal bidirectional switch circuit, for generating a PWM waveform signal by using the sine chopping waveform signal;

The LED constant current driving circuit is connected with the PWM waveform signal generating circuit, and is used to control the on and off of the LED light source by using the PWM waveform signal, so as to realize the constant current PWM driving of the LED.

Each component in the LED constant current driving circuit of this embodiment will be described in detail below.

Three-terminal bidirectional switch circuit

FIG. 2 is a schematic structural diagram of a three-terminal bidirectional switch circuit in the LED constant current drive circuit shown in FIG. 1 . Please refer to Figure 2, the triac circuit includes:

The double RC delay loop, whose input end is connected to the first end of the AC power supply V _ac , is used to delay the output signal of the AC power supply V _ac , including:

The first capacitor C1, the first end of which is connected to the first end of the AC power supply V _ac ;

The second capacitor C2, the first end of which is connected to the first end of the AC power supply V _ac ;

A fourth resistor R4, the first terminal of which is connected to the second terminal of the first capacitor C1, and the second terminal of which is connected to the second terminal of the second capacitor C2;

a third resistor R3, the first terminal of which is connected to the second terminal of the first capacitor C1;

A three-terminal bidirectional switch (TRIAC), its second anode end is connected to the first end of the AC power supply V _ac , its control end is connected to the second end of the second capacitor C2 in the double RC delay loop through a bidirectional trigger diode (DIAC), Its first anode end is connected to the second end of the third resistor R3;

A first load resistor R1 and a second load resistor R2 connected in series, wherein the first end of the first load resistor R1 is connected to the second end of the AC power supply V _ac , and the second end of the second load resistor R2 is connected to the third The second terminal of resistor R3.

Wherein, the first end of the first load resistor R1 is used as the first output end of the tri-terminal bidirectional switch circuit, and the second end thereof is used as the second output end of the tri-terminal bidirectional switch circuit.

In this embodiment, the AC power supply V _ac is an AC voltage of 220V.

The double RC delay loop can delay the start of the triac until it reaches the trigger point voltage of the bidirectional trigger diode DIAC. In addition, both the third resistor R3 and the fourth resistor R4 in the double RC delay loop can be adjusted to change the conduction time.

In addition, the resistance values of the first load resistor R1 and the second load resistor R2 can also be adjusted. By adjusting the resistance values of the two, the amplitude of the output signal of the three-terminal bidirectional switch circuit can be changed.

PWM waveform signal generation circuit

FIG. 3 is a schematic structural diagram of a PWM waveform signal generating circuit in the LED constant current driving circuit shown in FIG. 1 . Please refer to Figure 3, the PWM waveform signal generating circuit includes:

A bridge rectifier circuit Z composed of four diodes, its first end is connected to the first output end of the three-terminal bidirectional switch circuit, its second end is connected to the second output end of the three-terminal bidirectional switch circuit, and its third end connected to ground;

The zero-crossing comparator EA1 has its negative phase input terminal connected to the ground, its positive phase input terminal connected to the fourth terminal of the bridge rectifier circuit Z, and its output terminal is the output terminal of the PWM waveform signal generating circuit.

The bridge rectifier circuit Z is used to rectify the sinusoidal chopping signal output by the three-terminal bidirectional switch circuit to obtain the rectification waveform signal of the sinusoidal chopping waveform, and the zero-crossing comparator EA1 is used to convert the rectification waveform signal of the sinusoidal chopping waveform into PWM waveform signal.

LED constant current drive circuit

FIG. 4 is a schematic structural diagram of the LED constant current driving circuit in the LED constant current driving circuit shown in FIG. 1 . Please refer to Figure 4, the LED constant current drive circuit includes:

Voltage comparator EA2, its positive phase input terminal is connected to the reference voltage - about 1.43V (related to the current flowing through the LED and the resistance values of R6 and R7);

Transistor Q, its base is connected to the output end of the PWM waveform signal generating circuit, its collector is connected to the negative pole of the LED light source, and connected to the ground through a feedback resistor RT with a positive temperature coefficient;

Amplifier Av, its positive input terminal is connected to the ground through the seventh resistor R7, its negative input terminal is connected to the emitter of the transistor Q; its output terminal is connected to its positive output terminal through the sixth resistor R6, and connected to the voltage Negative input of comparator EA2;

The gate of the adjustment transistor PMOS is connected to the output terminal of the voltage comparator EA2 , the drain is connected to the anode of the LED light source, and the source is connected to the circuit power supply V _IN .

When the circuit power supply V _IN is powered on, the input voltage varies from 6.5V to 30V, and the reference voltage generates a reference voltage, which is input to the non-inverting input terminal of the voltage comparator EA2. Use the positive temperature coefficient of the feedback resistor RT to set the current flowing through the LED. The Av amplifier amplifies the detection voltage of the positive temperature coefficient feedback resistor RT proportionally and then inputs it to the negative phase input terminal of the voltage comparator EA2. Amplifier Av, voltage comparator EA2 and adjustment tube PMOS form a negative feedback network for regulating the output current. When the output current changes, the voltage across the positive temperature coefficient feedback resistor RT is amplified and compared with the reference voltage, and the difference between the two is amplified and used to control the gate of the adjustment tube, thereby stabilizing the output current. The PWM signal output by the PWM waveform signal generating circuit can control the turn-on and turn-off of the triode Q so as to realize the dimming control of the LED light source. A resistor with a positive temperature coefficient has a positive temperature coefficient. As the ambient temperature rises, its resistance value becomes larger, so that the current flowing through the LED light source becomes smaller, which in turn reduces the power consumption of the circuit and lowers the temperature. The resistor with a positive temperature coefficient can play a role of temperature negative feedback, which is beneficial to prevent the temperature rise of the LED light source from causing problems such as a decrease in efficiency and a decrease in life.

In the present invention, the adjusting transistor can be a PMOS or NMOS transistor. Wherein, the LED light source is a single LED tube or an LED array composed of multiple series and/or parallel LED tubes.

FIG. 5 is a waveform signal diagram of some nodes in the LED constant current PWM driving circuit shown in FIG. 1 . Please refer to FIG. 5 , the dotted line (light-colored line) corresponds to the input sinusoidal signal, and the solid line (dark-colored line) represents the signals P0, P1 and P2 extracted from some nodes in the LED constant current PWM driving circuit of this embodiment. P0 is a sinusoidal chopping waveform signal output by the three-terminal bidirectional switch circuit. From the signal waveform of P0, the three-terminal bidirectional switch circuit accurately converts the 220V AC signal output by the AC power supply V _ac into its sinusoidal chopping waveform signal . P1 is the rectified waveform signal of the sinusoidal chopping waveform rectified by the bridge rectifier circuit Z, and P2 is the PWM waveform signal output by the PWM waveform signal generating circuit.

So far, the introduction of the LED constant current PWM driving circuit of this embodiment is completed.

In the second exemplary embodiment of the present invention, a three-primary-color LED mixed light driving circuit based on the LED constant current PWM driving circuit is also provided.

FIG. 6 is a schematic structural diagram of a three-primary-color LED mixed light driving circuit according to an embodiment of the present invention. Please refer to FIG. 6 , the three-primary-color LED mixed-light driving circuit in this embodiment includes: a first LED constant-current PWM driving circuit, a second LED constant-current PWM driving circuit and a third LED constant-current PWM driving circuit. The three LED constant-current PWM drive circuits are the above-mentioned LED constant-current PWM drive circuits, and their input terminals are connected to the AC power supply V _AC to drive the red LED light source, the blue light LED light source and the green light LED light source respectively.

Through the third resistor R3 and the fourth resistor R4 in the LED constant current PWM drive circuit, the conduction time of the three-terminal bidirectional switch circuit can be changed, thereby changing the duty ratio of the sinusoidal chopping waveform output by it, thereby adjusting the PWM waveform signal. The duty cycle, and then realize the dimming of the LED light source. Wherein, the adjustable range of the third resistor R3 and the fourth resistor R4 is 300 kΩ˜600 kΩ, which is determined by the AC frequency and the capacitance values of the first capacitor C1 and the second capacitor C2. By dimming the three LED light sources in the three LED constant-current PWM drive circuits, the ratio of the RGB three-color light can be changed, thereby adjusting the color temperature of the RGB three-color light after mixing.

So far, two embodiments of the present invention have been described in detail with reference to the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the LED constant-current PWM drive circuit and the three-primary-color LED mixed light drive circuit of the present invention.

In addition, the above definitions of each element and method are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and those skilled in the art can easily modify or replace them.

To sum up, the present invention provides an LED constant-current PWM driving circuit and a three-primary-color LED mixed-light driving circuit. The LED constant current PWM driving circuit changes the capacitive load of the LED light source into a resistive load, thereby ensuring a high power factor without affecting the quality of the entire power grid, and has extremely high application value.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. a LED constant current PWM drive circuit, is characterized in that, comprising:

Three terminal bidirectional switching circuit, is connected with AC power, and the sinusoidal ac signal for AC power being provided converts sinusoidal chopped waveform signal to;

PWM waveform produces circuit, is connected with described three terminal bidirectional switching circuit, produces PWM waveform for utilizing described sinusoidal chopped waveform signal;

Constant current driver circuit for LED, produces circuit with described PWM waveform and is connected, and for the turn-on and turn-off utilizing described PWM waveform to control LED light source, thus the constant current PWM realizing LED drives, and comprising:

Voltage comparator (EA2), its normal phase input end is connected to reference voltage;

Triode (Q), its base stage is connected to the output that described PWM waveform produces circuit, and its collector electrode is connected to the negative pole of LED light source, and is connected to ground by the feedback resistance (RT) of positive temperature coefficient;

Amplifier (Av), its normal phase input end is connected to ground by the 7th resistance (R7), and its negative input is connected to the emitter of triode (Q); Its output is connected to its forward output by the 6th resistance (R6), and is connected to the negative input of voltage comparator (EA2);

Correctional tube, its grid is connected to the output of voltage comparator (EA2), and its drain electrode is connected to the positive pole of LED light source, and its source electrode is connected to circuit power (V _iN).

2. LED constant current PWM drive circuit according to claim 1, is characterized in that, described Correctional tube is PMOS or NMOS tube.

3. LED constant current PWM drive circuit according to claim 1, is characterized in that, described circuit power V _iNchange range of input voltage is 6.5V ~ 30V.

4. LED constant current PWM drive circuit according to claim 1, is characterized in that, described LED light source is the LED array of the LED pipe composition of single led pipe or multiple series connection and/or parallel connection.

5. LED constant current PWM drive circuit according to any one of claim 1 to 4, it is characterized in that, the sinusoidal chopped waveform signal that described three terminal bidirectional switching circuit exports is exported by its first output and the second output, and described PWM waveform produces circuit and comprises:

Bridge rectifier (Z), be made up of four diodes, its first end is connected to the first output of described three terminal bidirectional switching circuit, its second end is connected to the second output of described three terminal bidirectional switching circuit, its three-terminal link is to ground, and the sinusoidal chopping signal rectification that three terminal bidirectional switching circuit exports by this bridge rectifier (Z) obtains the rectified waveform signal of sinusoidal chopped waveform;

Zero-crossing comparator (EA1), its negative-phase input is connected to ground, its normal phase input end is connected to the 4th end of described bridge rectifier (Z), its output is the output that PWM waveform produces circuit, and the rectified waveform signal that described bridge rectifier (Z) exports sinusoidal chopped waveform is changed into PWM waveform by this zero-crossing comparator (EA1).

6. LED constant current PWM drive circuit according to any one of claim 1 to 4, is characterized in that, described three terminal bidirectional switching circuit comprises:

Two RC delay loop, its input is connected to AC power V _acfirst end, for AC power V _acoutput signal postpones, and comprising:

First electric capacity (C1), its first end is connected to AC power V _acfirst end;

Second electric capacity (C2), its first end is connected to AC power V _acfirst end;

4th resistance (R4), its first end is connected to the second end of the first electric capacity (C1), and its second end is connected to the second end of the second electric capacity (C2);

3rd resistance (R3), its first end is connected to the second end of the first electric capacity (C1);

Three terminal bidirectional switch (TRIAC), its second plate end is connected to AC power V _acfirst end, it controls extreme the second end being connected to the second electric capacity (C2) in described pair of RC delay loop by bidirectional trigger diode (DIAC), and its first anode end is connected to the second end of the 3rd resistance (R3);

First load resistance (R1) of mutual series connection and the second load resistance (R2), wherein, the first end of the first load resistance (R1) is connected to AC power V _acthe second end, the second end of the second load resistance (R2) is connected to the second end of the 3rd resistance (R3);

Wherein, the first end of the first load resistance (R1) is as the first output of this three terminal bidirectional switching circuit, and its second end is as the second output of this three terminal bidirectional switching circuit.

7. LED constant current PWM drive circuit according to claim 6, is characterized in that, described AC power V _acexport the alternating voltage of 220V.

8. LED constant current PWM drive circuit according to claim 6, it is characterized in that, described 3rd resistance (R3) and the 4th resistance (R4) are adjustable resistance, wherein, the adjustable extent of the 3rd resistance (R3) and the 4th resistance (R4) is between 300k Ω ~ 600k Ω;

By regulating the resistance of the 3rd resistance (R3) and the 4th resistance (R4), change the ON time of described three terminal bidirectional switching circuit, thus change the duty ratio that it exports sinusoidal chopped waveform, and then regulate PWM waveform to produce the duty ratio of circuit output PWM waveform, the final brightness regulating LED light source.

9. a three-primary color LED mixed light drive circuit, is characterized in that, comprising: the first LED constant current PWM drive circuit, the second LED constant current PWM drive circuit and the 3rd LED constant current PWM drive circuit;

Wherein, these three LED constant current PWM drive circuit are the LED constant current PWM drive circuit according to any one of claim 1 to 8, drive red-light LED light source, blue light LED light source and green light LED light source respectively.