A thyristor LED dimming circuit

Abstract

The present invention discloses a thyristor LED dimming circuit, the thyristor LED dimming circuit comprises a thyristor dimmer, an LED driving circuit and a constant current control circuit, the LED driving circuit is arranged between the thyristor dimmer and the LED, the constant current control circuit is respectively connected to the LED and the LED driving circuit, the LED driving circuit comprises an input rectifier circuit, an auxiliary rectifier circuit, an input filter circuit, a flyback switch circuit, a first output rectifier circuit, a first output filter circuit, a second output rectifier circuit and a second output filter circuit, the constant current control circuit comprises a sampling circuit, a constant current and constant voltage controller, an optical coupler, a PWM controller and peripheral circuits. The implementation of the present invention can overcome the problem of the thyristor dimmer being unable to work stably when used for LED dimming and the LED flickering during the dimming process, can effectively avoid the LED flickering problem caused by the control chip power supply voltage being in a critical state during the dimming process, and can also avoid the problem of LED color change caused by using the thyristor dimmer to directly dim the LED.

Description

Technical Field

[0001] The invention relates to the field of LED dimming, and in particular to a thyristor LED dimming circuit. Background Art

[0002] The traditional thyristor dimmer dimming is to change the average current flowing through the load by adjusting the conduction angle of the thyristor, thereby dimming the incandescent lamp. Since the incandescent lamp consumes a lot of power and emits light through thermal effects, there is thermal inertia, so this dimming method can achieve a good dimming effect.

[0003] As LED lighting becomes more and more popular, dimming LED light sources has greater practical significance. When thyristor dimmers are used with LED light sources, there is a problem that the load current is small, causing the thyristor dimmer to fail to work normally or stably, or the LED flickers due to abnormal shutdown of the thyristor or the LED driver chip during the dimming process. At the same time, using a thyristor dimmer to directly dim the LED light source will also affect the color change of the LED. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a thyristor LED dimming circuit, which can solve the problems existing in the existing thyristor LED dimming method.

[0005] In order to solve the above technical problems, the present invention provides a thyristor LED dimming circuit, the thyristor LED dimming circuit includes a thyristor dimmer, an LED driving circuit and a constant current control circuit, the LED driving circuit is arranged between the thyristor dimmer and the LED, the constant current control circuit is connected to the LED and the LED driving circuit respectively, the LED driving circuit includes an input rectifier circuit, an auxiliary rectifier circuit, an input filter circuit, a flyback switch circuit, a first output rectifier circuit, a first output filter circuit, a second output rectifier circuit and a second output filter circuit, the constant current control circuit includes a sampling circuit, a constant current and constant voltage controller, an optocoupler, a PWM controller and a peripheral circuit; the thyristor dimmer is connected to the input end of the flyback switch circuit through the input rectifier circuit and the input filter circuit in sequence, and the thyristor dimmer is also connected to the power supply end of the PWM controller through the auxiliary rectifier circuit; the flyback The switch circuit includes a transformer and a switch tube, the transformer includes a primary coil, a secondary coil and an auxiliary coil, the primary coil is the input end of the flyback switch circuit and is grounded through the switch tube, the secondary coil is the first output end of the flyback switch circuit, the auxiliary coil is the second output end of the flyback switch circuit, the first output end is connected to the power supply end of the light emitter of the optocoupler, the power supply end of the constant current and constant voltage controller and the LED through the first output rectifier circuit and the first output filter circuit in sequence, the second output end is connected to the PWM controller and the power supply end of the light receiver of the optocoupler through the second output rectifier circuit and the second output filter circuit in sequence; the LED is connected to the sampling current input end of the constant current and constant voltage controller through the sampling circuit, the output end of the constant current and constant voltage controller is connected to the feedback end of the PWM controller through the optocoupler, and the driving end of the PWM controller is connected to the switch tube in the flyback switch circuit.

[0006] Preferably, the input rectifier circuit is a full-bridge rectifier bridge, which includes two AC input terminals, an output positive electrode and an output negative electrode. The two AC input terminals are used to connect a thyristor dimmer, the output positive electrode is connected to the input terminal of the filter circuit, and the output negative electrode is grounded.

[0007] Preferably, the auxiliary rectification circuit is composed of a half-bridge rectifier bridge and two rectifier diodes in the full-bridge rectifier bridge, the half-bridge rectifier bridge includes two AC input terminals and one output positive pole, the two AC input terminals of the half-bridge rectifier bridge are respectively connected to the two AC input terminals of the full-bridge rectifier bridge, and connected to the two output terminals of the thyristor dimmer; the output positive pole of the half-bridge rectifier bridge is connected to the power supply terminal of the PWM controller.

[0008] Preferably, the output positive pole of the half-bridge rectifier is connected to the power supply end of the PWM controller through a voltage divider circuit, the voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor, the output positive pole of the half-bridge rectifier is respectively connected to the power supply end of the PWM controller and one end of the second voltage divider resistor through the first voltage divider resistor, and the other end of the second voltage divider resistor is grounded.

[0009] Preferably, filter capacitors are provided at both ends of the second voltage-dividing resistor.

[0010] Preferably, the flyback switch circuit further includes an RCD absorption circuit, and the RCD absorption circuit is connected in parallel to both ends of the primary coil of the transformer in the flyback switch circuit.

[0011] Preferably, the second output rectifier circuit is grounded through a limiting circuit, and the limiting circuit includes a current limiting resistor and a voltage regulator diode connected in series, one end of the current limiting resistor is connected to the second output rectifier circuit, and the other end is connected to the power supply end of the PWM controller.

[0012] Preferably, the first output rectifier circuit is grounded via a rectifier diode, a current limiting resistor and a voltage regulator diode in sequence, a filter capacitor is connected in parallel at both ends of the voltage regulator diode, and the power supply end of the light emitter of the optocoupler is connected to the node between the current limiting resistor and the voltage regulator diode.

[0013] Preferably, the switch tube in the flyback switch circuit is grounded via a first sampling resistor, and is also connected to the PWM controller via a first buffer resistor.

[0014] Preferably, the sampling circuit comprises a second sampling resistor and a second buffer resistor, the LED is connected to the constant current and constant voltage controller via the second buffer resistor, and the LED is grounded via the second sampling resistor.

[0015] The beneficial effects of implementing the present invention are:

[0016] The thyristor LED dimming circuit provided by the present invention inputs alternating current into a thyristor dimmer, the thyristor dimmer outputs chopped alternating current, the chopped alternating current is used to synchronously control the opening and closing of a PWM controller, the LED driving circuit outputs a pulse signal to an LED, and then the pulse signal is subjected to constant current processing by a constant current control circuit to form a periodic constant current square wave pulse. The thyristor dimmer is adjusted to dim the LED. Since the switching frequency of the PWM controller is very high, the problem of the thyristor dimmer being unable to work stably when used for LED dimming and the LED flickering during the dimming process can be overcome. On the other hand, the auxiliary rectifier circuit provides a starting voltage to the PWM controller, so that the power supply of the PWM controller is synchronized with the chopped alternating current, which can effectively avoid the LED flickering problem caused by the critical state of the power supply voltage of the PWM controller during the dimming process. In addition, the present invention converts the simulated chopped alternating current output by the thyristor dimmer into a constant current square wave pulse to power the LED, and can also avoid the LED color change problem caused by the direct dimming of the LED using the thyristor dimmer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a dimming principle diagram provided by the present invention;

[0018] Figure 2 It is a structural diagram of a dimming circuit provided by the present invention;

[0019] Figure 3 It is a circuit diagram of the dimming circuit provided by the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. It is hereby stated that the directional terms such as up, down, left, right, front, back, inside, outside, etc. that appear or will appear in the text of the present invention are only based on the accompanying drawings of the present invention, and are not specific limitations of the present invention.

[0021] like Figure 1 As shown, the present invention provides an LED dimming circuit, which includes a thyristor dimmer 1, an LED driving circuit 2 and a constant current control circuit 3. The LED driving circuit 2 is arranged between the thyristor dimmer 1 and the LED 4, and the constant current control circuit 3 is connected to the LED 4 and the LED driving circuit 2 respectively. The LED driving circuit 2 is used to drive the LED 4, and combines with the constant current control circuit 3 to realize constant current driving.

[0022] like Figure 2As shown, the LED driving circuit 2 includes an input rectifying circuit 201, an auxiliary rectifying circuit 203, an input filtering circuit 202, a flyback switching circuit 204, a first output rectifying circuit 205, a first output filtering circuit 206, a second output rectifying circuit 207 and a second output filtering circuit 208. The constant current control circuit 3 includes a sampling circuit 301, a constant current and constant voltage controller 302, an optocoupler 303, a PWM controller 304 and peripheral circuits.

[0023] The flyback switch circuit 204 includes a transformer and a switch tube. The transformer includes a primary coil, a secondary coil and an auxiliary coil. The primary coil is the input end of the flyback switch circuit 204 and is grounded through the switch tube. The secondary coil is the first output end of the flyback switch circuit 204. The auxiliary coil is the second output end of the flyback switch circuit 204.

[0024] The thyristor dimmer 1 is connected to the input end of the flyback switch circuit 204 through the input rectification circuit 201 and the input filtering circuit 202 in sequence, and performs rectification and filtering on the chopped AC power passing through the thyristor dimmer 1 and then transmits it to the flyback switch circuit 204 .

[0025] The thyristor dimmer 1 is also connected to the power supply end of the PWM controller 304 through the auxiliary rectifier circuit 203, and the drive output end of the PWM controller 304 is connected to the switch tube in the flyback switch circuit 204 to control the on and off of the switch tube. When the power supply voltage meets the starting voltage, the PWM controller 304 is started to control the on and off of the switch tube; when the starting voltage is not met, the PWM controller 304 is turned off to control the switch tube to be completely turned off.

[0026] The first output end of the flyback switch circuit 204 is connected to the power supply end of the light emitter of the optocoupler 303, the power supply end of the constant current and constant voltage controller 302 and the LED through the first output rectifier circuit 205 and the first output filter circuit 206 in sequence, and is used to drive the LED and provide working power to the light emitter of the optocoupler 303 and the constant current and constant voltage controller 302.

[0027] The second output end of the flyback switch circuit 204 is connected to the power supply end of the PWM controller 304 and the light receiver of the optocoupler 303 through the second output rectifier circuit 207 and the second output filter circuit 208 in sequence, so as to provide working power to the PWM controller 304 and the light receiver of the optocoupler 303.

[0028] The LED4 is connected to the input end of the constant current and constant voltage controller 302 through the sampling circuit 301, that is, the collected LED current signal is converted into a voltage signal, and then input into the constant current and constant voltage controller 302. The output end of the constant current and constant voltage controller 302 is connected to the feedback end of the PWM controller 304 through the optical coupler 303. The constant current and constant voltage controller 302 outputs an error signal to the optical coupler 303 according to the voltage signal collected by the sampling circuit 301, and further feeds back to the PWM controller 304 to control the duty cycle of the switch tube and realize the constant current drive of the LED.

[0029] The present invention controls the on and off of the PWM controller 304 through a thyristor dimmer, further controls the on and off of the switch tube, outputs a pulse DC signal through a flyback switch circuit 204, drives LED4 to work, controls the on (or off) time of the PWM controller 304 by changing the conduction angle of the thyristor dimmer, changes the duty cycle of the output pulse DC signal, and realizes LED dimming. At the same time, the constant current and constant voltage controller 302 outputs an error signal to the optocoupler 303 according to the voltage signal collected by the sampling circuit 301, and further feeds back to the PWM controller 304 to control the duty cycle of the switch tube and realize constant current drive of the LED. The present invention connects the auxiliary rectifier circuit 203 with the power supply end of the PWM controller 304 to start the operation of the PWM controller 304, rather than directly connecting the power supply end of the PWM controller 304 with the input filter circuit. This is because when the thyristor dimmer 1 is turned off, there is residual charge in the capacitor in the input filter circuit, and the power supply end voltage of the PWM controller 304 cannot immediately become zero. This problem can be avoided by the auxiliary rectifier circuit 203, so that the power supply end voltage of the PWM controller follows the voltage change of the thyristor dimmer output, thereby overcoming the LED flickering problem caused by the PWM controller power supply voltage being in a critical state.

[0030] like Figure 3As shown, the input rectifier circuit 201 is a full-bridge rectifier bridge, and the full-bridge rectifier bridge includes two AC input terminals, an output positive electrode and an output negative electrode. The two AC input terminals are used to connect the thyristor dimmer 1, the output positive electrode is connected to the input terminal of the input filter circuit, and the output negative electrode is grounded. Further, the auxiliary rectifier circuit 203 is composed of a half-bridge rectifier bridge and two rectifier diodes in the full-bridge rectifier bridge. The half-bridge rectifier bridge includes two AC input terminals and an output positive electrode. The two AC input terminals of the half-bridge rectifier bridge are respectively connected to the two AC input terminals of the full-bridge rectifier bridge, and the output positive electrode of the half-bridge rectifier bridge is connected to the power supply terminal of the PWM controller 304 through a first voltage-dividing resistor. In the present invention, the auxiliary rectifier circuit 203 is formed by the two rectifier diodes in the input rectifier circuit 201 and another half-bridge rectifier bridge, which can reduce the manufacturing cost without affecting the rectification effect.

[0031] Preferably, the output positive pole of the half-bridge rectifier is connected to the power supply terminal of the PWM controller 304 through a voltage divider circuit, and the voltage divider circuit includes a first voltage divider resistor R7 and a second voltage divider resistor R5. The output positive pole of the half-bridge rectifier is connected to the power supply terminal of the PWM controller 304 (U2) and one end of the second voltage divider resistor R5 through the first voltage divider resistor R7, and the other end of the second voltage divider resistor R5 is grounded. The resistance of R7 is relatively large (500k~1M) relative to R5, providing a starting voltage for U2 and also having a current limiting effect. Furthermore, filter capacitors are provided at both ends of the second voltage divider resistor R5 to reduce the interference of ripple on the operation of the PWM controller 304.

[0032] Preferably, the flyback switch circuit 204 also includes an RCD absorption circuit, which is connected in parallel to the two ends of the primary coil of the transformer in the flyback switch circuit. The RCD absorption circuit includes an absorption resistor R1, an absorption capacitor C2 and an absorption diode D3 to prevent high spike voltage from appearing on the drain of the switch tube and damaging the switch tube.

[0033] Furthermore, the second output rectifier circuit 207 is grounded through a limiting circuit, the limiting circuit includes a current limiting resistor R4 and a voltage stabilizing diode ZD1 connected in series, one end of the current limiting resistor R4 is connected to the second output rectifier circuit, and the other end is connected to the power supply terminal of the PWM controller. The limiting circuit can prevent the transformer from generating high voltage spikes and clamp voltages higher than 18V to prevent damage to the PWM controller.

[0034] More preferably, the first output rectifier circuit 205 is grounded in sequence through a rectifier diode D2, a current limiting resistor R3 and a voltage zener diode ZD2, filter capacitors C6 and C9 are connected in parallel at both ends of the voltage zener diode ZD2, and the power supply end of the light emitter of the optocoupler 303 is connected to the node between the current limiting resistor R3 and the voltage zener diode ZD2, which respectively provide rectification, voltage stabilization and filtering effects for the power supply process of the optocoupler, thereby stabilizing the working voltage of the optocoupler.

[0035] Preferably, the switch tube in the flyback switch circuit 204 is grounded through a first sampling resistor R15, and is also connected to the PWM controller through a first buffer resistor R12. The first sampling resistor R15 is used to collect the primary coil current of the flyback switch circuit, and input it to the sampling pin of the PWM controller through the first buffer resistor R12, so as to control the primary coil current not to exceed a certain peak value, thereby playing a current limiting protection role.

[0036] Furthermore, the sampling circuit 301 includes a second sampling resistor Rsense and a second buffer resistor R17, the LED is connected to the constant current and constant voltage controller through the second buffer resistor R17, and the LED is grounded through the second sampling resistor Rsense.

[0037] At the same time, the constant current and constant voltage controller is preferably TSM1052, but not limited thereto, and the TSM1052 includes pins: OUT, VCC, Vctrl, Ictrl, Vsense, GND. Its peripheral circuit includes a negative feedback network composed of C7 and R9, which is connected in parallel between OUT and Vctrl to stabilize the operation of U3; it also includes a current limiting resistor R8, one end of which is connected to OUT and the other end is connected to the optocoupler to protect the normal operation of the optocoupler; it also includes C8 and R16 necessary for the operation of the constant current and constant voltage controller, and OUT is grounded through C8 and R16 in turn; it also includes R6 and R14, one end of R6 is connected to the positive electrode of the rectifier diode D2, and the other end is connected to Vctrl, Vctrl is grounded through R14, and forms a voltage stabilizing circuit with the voltage loop op amp inside the constant current and constant voltage controller to stabilize the working voltage of the constant current and constant voltage controller. The PWM controller is preferably NCP1606, but not limited thereto, and the NCP1606 includes pins: FB, CTRL, CT, VCC, GND, DRV, ZCD, CS. Its peripheral circuit includes a gate resistor R10, which is connected to the gate of the switch tube and the other end is connected to DRV, and is used to adjust the steepness of the leading and trailing edges of the control pulse and prevent oscillation; it also includes R11 and R13, which are necessary for operation, one end of R11 is connected to FB, and the other end is respectively connected to the output end of the optocoupler and grounded through R13.

[0038] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A thyristor LED dimming circuit, comprising a thyristor dimmer, an LED drive circuit and a constant current control circuit, wherein the LED drive circuit is arranged between the thyristor dimmer and the LED, and the constant current control circuit is connected to the LED and the LED drive circuit respectively, characterized in that: The LED driving circuit includes an input rectifier circuit, an auxiliary rectifier circuit, an input filter circuit, a flyback switch circuit, a first output rectifier circuit, a first output filter circuit, a second output rectifier circuit and a second output filter circuit, and the constant current control circuit includes a sampling circuit, a constant current and constant voltage controller, an optocoupler, a PWM controller and peripheral circuits; The flyback switch circuit includes a transformer and a switch tube, the transformer includes a primary coil, a secondary coil and an auxiliary coil, the primary coil is the input end of the flyback switch circuit and is grounded through the switch tube, the secondary coil is the first output end of the flyback switch circuit, the auxiliary coil is the second output end of the flyback switch circuit, the first output end is connected to the power supply end of the light emitter of the optocoupler, the power supply end of the constant current and constant voltage controller and the LED through the first output rectifier circuit and the first output filter circuit in sequence, and the second output end is connected to the PWM controller and the power supply end of the light receiver of the optocoupler through the second output rectifier circuit and the second output filter circuit in sequence; The thyristor dimmer is connected to the input end of the flyback switch circuit through the input rectification circuit and the input filtering circuit in sequence, and the thyristor dimmer is also connected to the power supply end of the PWM controller through the auxiliary rectification circuit; The LED is connected to the sampling current input terminal of the constant current and constant voltage controller through a sampling circuit, the output terminal of the constant current and constant voltage controller is connected to the feedback terminal of the PWM controller through an optical coupler, and the driving terminal of the PWM controller is connected to the switch tube in the flyback switch circuit; The peripheral circuit includes a negative feedback network composed of capacitor C7 and resistor R9, a current limiting resistor R8, capacitor C8, resistor R16, resistor R6, and resistor R14. The negative feedback network is used to stabilize the constant current and constant voltage controller; the current limiting resistor R8 is used to protect the normal operation of the optocoupler; the output end of the constant current and constant voltage controller is grounded through capacitor C8 and resistor R16 in turn; resistor R6 and resistor R14 are used to stabilize the working voltage of the constant current and constant voltage controller.

2. The thyristor LED dimming circuit according to claim 1, characterized in that: The input rectifier circuit is a full-bridge rectifier bridge, which includes two AC input terminals, an output positive electrode and an output negative electrode. The two AC input terminals are used to connect to a thyristor dimmer, the output positive electrode is connected to the input terminal of the filter circuit, and the output negative electrode is grounded.

3. The thyristor LED dimming circuit according to claim 2, characterized in that: The auxiliary rectification circuit is composed of a half-bridge rectifier bridge and two rectifier diodes in the full-bridge rectifier bridge. The half-bridge rectifier bridge includes two AC input terminals and an output positive pole. The two AC input terminals of the half-bridge rectifier bridge are respectively connected to the two AC input terminals of the full-bridge rectifier bridge, and the output positive pole of the half-bridge rectifier bridge is connected to the power supply terminal of the PWM controller.

4. The thyristor LED dimming circuit according to claim 3, characterized in that: The output positive pole of the half-bridge rectifier is connected to the power supply end of the PWM controller through a voltage divider circuit, and the voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor. The output positive pole of the half-bridge rectifier is connected to the power supply end of the PWM controller and one end of the second voltage divider resistor through the first voltage divider resistor, and the other end of the second voltage divider resistor is grounded.

5. The thyristor LED dimming circuit according to claim 4, characterized in that: Filter capacitors are provided at both ends of the second voltage-dividing resistor.

6. The thyristor LED dimming circuit according to claim 1, characterized in that: The flyback switch circuit further includes an RCD absorption circuit, which is connected in parallel to both ends of the primary coil of the transformer in the flyback switch circuit.

7. The thyristor LED dimming circuit according to claim 1, characterized in that: The second output rectifier circuit is grounded through a limiting circuit, and the limiting circuit includes a current limiting resistor and a voltage regulator diode connected in series, one end of the current limiting resistor is connected to the second output rectifier circuit, and the other end is connected to the power supply end of the PWM controller.

8. The thyristor LED dimming circuit according to claim 1, characterized in that: The first output rectifier circuit is grounded via a rectifier diode, a current limiting resistor and a voltage regulator diode in sequence, a filter capacitor is connected in parallel at both ends of the voltage regulator diode, and the power supply end of the light emitter of the optocoupler is connected to a node between the current limiting resistor and the voltage regulator diode.

9. The thyristor LED dimming circuit according to claim 1, characterized in that: The switch tube in the flyback switch circuit is grounded through a first sampling resistor, and is also connected to the PWM controller through a first buffer resistor.

10. The thyristor LED dimming circuit according to claim 1, characterized in that: The sampling circuit includes a second sampling resistor and a second buffer resistor, the LED is connected to the constant current and constant voltage controller through the second buffer resistor, and the LED is grounded through the second sampling resistor.

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