Single-stage two-switch LED drive circuit without electrolytic capacitor

Abstract

The invention discloses a single-stage two-switch electrolytic capacitor-free LED drive circuit, which comprises an electrolytic capacitor-free LED drive circuit, the LED drive circuit without the electrolytic capacitor comprises an input voltage Vin, an input rectifier diode VDr1, an input rectifier diode VDr2, an input rectifier diode VDr3, an input rectifier diode VDr4, a transformer Tr, a switch tube Q1, a secondary side freewheel diode VDo, an output capacitor Co, an energy storage element Ca, a switch tube Q2, an auxiliary diode VDs, an inductor L1 and an inductor L2. According to the circuit, the flyback converter and the auxiliary energy storage circuit are highly integrated in a switching tube sharing mode, switching devices are reduced, the circuit structure is simple, charging and discharging balance of an energy storage capacitor is achieved by controlling the time of simultaneous switching-on and simultaneous switching-off of the two switching tubes, low-frequency ripples of output current are restrained, and the output current is improved. The auxiliary energy storage circuit absorbs leakage inductance energy and reduces the voltage amplitude at the drain end and the source end of the switch tube, so that the voltage stress of the switch tube is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of LED drive circuits, and in particular to a single-stage two-switch electrolytic capacitor-free LED drive circuit. Background Art

[0002] As the fourth generation of electric lighting sources, light-emitting diodes have the advantages of long service life, high luminous efficiency, energy saving and low carbon, and are widely used in various lighting fields. However, since traditional LED driver power supplies use electrolytic capacitors as the main energy storage devices, the life of electrolytic capacitors is far less than the life of the LEDs themselves, which affects the service life of traditional LED driver power supplies. At the same time, electrolytic capacitors are bulky and cannot meet the requirements of high power density. Therefore, it is of great significance to explore LED driver power supplies without electrolytic capacitors.

[0003] In order to free LED drive circuits from dependence on electrolytic capacitors, many scholars have conducted in-depth research on it. The main solutions to achieve electrolytic capacitor-free are divided into two aspects: optimizing the control strategy and optimizing the topology structure. Pulsating current drive and load dynamic adjustment methods are used to reduce the pulsating power difference by controlling the output power. A bidirectional Buck-Boost converter is connected in parallel at the output end to buffer the pulsating power difference between the input and output, thereby reducing the capacitance value.

[0004] However, the traditional electrolytic capacitor-free LED driver circuit has the following disadvantages: The traditional electrolytic capacitor-free LED driver circuit uses low-frequency pulsating current to drive the LED, causing extremely serious flickering problems that can cause certain damage to the health of the human retina. It is suitable for occasions where the LED light quality is not high or the circuit requires the auxiliary circuit voltage to be greater than the bus voltage, which makes the circuit switching device withstand voltage requirements higher and increases the circuit cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a single-stage two-switch electrolytic capacitor-free LED driving circuit to solve the extremely serious flicker problem caused by the low-frequency pulsating current driving the LED in the traditional electrolytic capacitor-free LED driving circuit proposed in the above background technology, which will cause certain damage to the health of the human retina. It is suitable for occasions where the LED luminous quality is not high or the circuit requires the auxiliary circuit voltage to be greater than the bus voltage, which makes the circuit switch device withstand voltage requirements higher, increasing the circuit cost.

[0006] To achieve the above object, the present invention provides the following technical solutions: a single-stage two-switch electrolytic capacitor-free LED driving circuit, comprising an electrolytic capacitor-free LED driving circuit, wherein the electrolytic capacitor-free LED driving circuit comprises an input voltage V in , Input rectifier diode VD r1 , Input rectifier diode VD r2, Input rectifier diode VD r3 , Input rectifier diode VD r4 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o , output capacitor C o , energy storage element C a , switch tube Q2, auxiliary diode VD s , inductor L1, inductor L2, secondary side freewheeling diode VD p and input capacitor C in , one end of the input voltage Vin and the input rectifier diode VD r1 One end of the input rectifier diode VD is connected r1 The other end of the input rectifier diode VD r2 One end and the input capacitor C in one end of the .

[0007] As a preferred technical solution of the present invention, the other end of the input voltage Vin is connected to the input rectifier diode VD r2 The other end and the input rectifier diode VD r4 One end of the input rectifier diode VD is connected r1 The other end of the input rectifier diode VD r3 One end of the input rectifier diode VD is connected r3 The other end and the input rectifier diode VD r4 The other end is connected to the input capacitor C in to the other end of the

[0008] As a preferred technical solution of the present invention, the input capacitor C in The surface of the secondary side freewheeling diode VD p One end of the secondary freewheeling diode VD is connected p The other end is connected to one end of the inductor L1 and the transformer T r The other end of the inductor L1 is connected to one end of the switch tube Q1, and the inductor L1 is connected to the transformer T r One end of the inductor L2 is connected therebetween, and the other end of the inductor L2 is connected to one end of the switch tube Q2.

[0009] As a preferred technical solution of the present invention, the connection between the inductor L1 and the switch tube Q1 and the energy storage element C a One end of the switch tube Q2 is connected to the energy storage element C a The other end and the secondary side freewheeling diode VD o One end of the inductor L2 is connected to the auxiliary diode VD sone end of the .

[0010] As a preferred technical solution of the present invention, the secondary side freewheeling diode VD o The other end and auxiliary diode VD s The other end of the output capacitor C o Connect both ends of .

[0011] As a preferred technical solution of the present invention, the energy storage element C a , switch tube Q1, switch tube Q2 and auxiliary diode VD s Form an auxiliary energy storage circuit.

[0012] As a preferred technical solution of the present invention, the input rectifier diode VD r1 , Input rectifier diode VD r2 , Input rectifier diode VD r3 , Input rectifier diode VD r4 , diode VD p 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o and output capacitor C o Form a flyback converter.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This circuit highly integrates the flyback converter and the auxiliary energy storage circuit by sharing the switch tube, reducing the number of switching devices and simplifying the circuit structure. By controlling the time when the two switches are simultaneously turned on and off, the charge and discharge balance of the energy storage capacitor is achieved, thereby suppressing the low-frequency ripple of the output current. The auxiliary energy storage circuit absorbs the leakage inductance energy, reducing the voltage amplitude across the drain and source of the switch tube, thereby reducing the voltage stress of the switch tube. 2. Compared with the traditional electrolytic capacitor-free LED driver circuit, the two-switch electrolytic capacitor-free LED driver circuit has fewer switching devices and a simpler control strategy. Experimental results show that when the auxiliary energy storage capacitor and the output filter capacitor are both 6.8μF, the output current ripple coefficient is 10.43% and the power factor reaches above 0.990, indicating that the circuit has good low-frequency ripple suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A circuit diagram of the present invention; Figure 2 FIG. 1 is a diagram of an equivalent circuit of the working mode of the energy storage capacitor in the discharge mode of the present invention; Figure 3 FIG b is a diagram of the working mode equivalent circuit of the energy storage capacitor in the discharge mode of the present invention; Figure 4 Figure c is the working mode equivalent circuit diagram of the energy storage capacitor in the discharge mode of the present invention; Figure 5 Figure d is the working mode equivalent circuit diagram of the energy storage capacitor in the discharge mode of the present invention; Figure 6 This is a working timing waveform diagram of the energy storage capacitor in the discharge mode of the present invention; Figure 7 This is the main experimental waveform diagram of the circuit under the rated input voltage of the present invention; Figure 8 This is a control block diagram of the electrolytic capacitor-free LED drive circuit of the present invention; Figure 9 The figure is a relationship curve diagram of the power factor, efficiency and input voltage of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] See also Figure 1-9 The present invention provides a single-stage two-switch electrolytic capacitor-free LED driving circuit, including an electrolytic capacitor-free LED driving circuit, an electrolytic capacitor-free LED driving circuit including an input voltage V in , Input rectifier diode VD r1 , Input rectifier diode VD r2 , Input rectifier diode VD r3 , Input rectifier diode VD r4 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o , output capacitor C o , energy storage element C a , switch tube Q2, auxiliary diode VD s , inductor L1, inductor L2, secondary side freewheeling diode VD p and input capacitor C in , one end of the input voltage Vin and the input rectifier diode VD r1 One end is connected to the input rectifier diode VD r1 The other end of the input rectifier diode VD r2 One end and the input capacitor C in one end of the .

[0017] The other end of the input voltage Vin is connected to the input rectifier diode VDr2 The other end and the input rectifier diode VD r4 One end is connected to the input rectifier diode VD r1 The other end of the input rectifier diode VD r3 One end is connected to the input rectifier diode VD r3 The other end and the input rectifier diode VD r4 The other end is connected to the input capacitor C in to the other end of the

[0018] Input capacitor C in The surface of the secondary side freewheeling diode VD p One end is connected to the secondary side freewheeling diode VD p The other end is connected to one end of the inductor L1 and the transformer T r The other end of the inductor L1 is connected to one end of the switch tube Q1, and the inductor L1 is connected to the transformer T r One end of the inductor L2 is connected therebetween, and the other end of the inductor L2 is connected to one end of the switch tube Q2.

[0019] The connection between the inductor L1 and the switch tube Q1 and the energy storage element C a One end of the switch tube Q2 is connected to the energy storage element C a The other end and the secondary side freewheeling diode VD o One end of the inductor L2 is connected to the auxiliary diode VD s one end of the .

[0020] Secondary side freewheeling diode VD o The other end and auxiliary diode VD s The other end of the output capacitor C o Connect both ends of .

[0021] Energy storage element C a , switch tube Q1, switch tube Q2 and auxiliary diode VD s Form an auxiliary energy storage circuit.

[0022] Input rectifier diode VD r1 , Input rectifier diode VD r2 , Input rectifier diode VD r3 , Input rectifier diode VD r4 , diode VD p 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o and output capacitor C o Form a flyback converter.

[0023] In the present invention, in combination with the description 2-6, mode 1 (t0-t1): the equivalent circuit is shown in FIG2, at time t0, the main switch Q1 is turned on, and the input source passes through the diode VD p , the main switch Q1 to the transformer T r The primary inductor L1 stores energy, and the primary inductor current i p and the current i flowing through the main switch tube Q1 Q1 Linear increase, the primary inductor current i p and the current i flowing through the main switch tube Q1 Q1 Expressed as: , Where, , V m is the input voltage subvalue, the equivalent circuit is as follows Figure 3 As shown, at time t1, the auxiliary switch tube Q2 is turned on and the energy storage capacitor C a Through the main switch tube Q1, diode VD s , the auxiliary switch tube Q2 stores energy in the secondary inductor L2, and the secondary current i s Increase linearly, and the relationship with time t is expressed as: , The voltage across the primary inductor L1 in this mode is clamped at nv Ca (t), where n is the transformer turns ratio, and the leakage inductance energy passes through the diode VD in a short time p , the switch tube Q1 feeds back to the input source, the diode VD p Since the leakage current drops to 0 and is cut off due to the reverse voltage, the diode VD p The cut-off conditions are: , Mode 3 (t2-t3), the equivalent circuit is as follows Figure 4 As shown, at time t2, the main switch Q1 is disconnected and the diode VD o Turn on, the secondary inductor L2 is connected through the switch tube Q2 and the diode VD s and VD o Powering the LED, the secondary current i s Linear decrease, the relationship with time t is expressed as: , Where V o is the LED output voltage, Mode 4 (t3-t4): Equivalent circuit is as follows Figure 5 As shown, at time t3, the energy of the transformer has been fully released, and the diode VD s , diode VDo is disconnected, output capacitor C o Supply power to LED; In order to verify the reliability of the proposed topological theoretical analysis, a prototype with an input of 110V / 50 Hz and an output of 30W / 390 mA was built. Figure 7 , is the rated input voltage v in =110V input current i in , energy storage capacitor voltage v Ca and output current I o The working waveform of Figure 7 It is known that the input current changes sinusoidally and has the same phase as the input voltage, so this topology achieves high power factor, and the output current ripple is controlled at about 15.5%. The output current ripple is well suppressed. This circuit highly integrates the flyback converter and the auxiliary energy storage circuit by sharing the switch tube, reducing the switching devices and having a simple circuit structure. By controlling the time when the two switch tubes are simultaneously turned on and off, the charge and discharge balance of the energy storage capacitor is achieved, thereby suppressing the low-frequency ripple of the output current. The auxiliary energy storage circuit absorbs the leakage inductance energy, reduces the voltage amplitude across the drain and source of the switch tube, and thus reduces the voltage stress of the switch tube. The experimental results show that when the auxiliary energy storage capacitor and the output capacitor are both 6.8μF, the output current ripple is controlled below 20%, and the power factor reaches above 0.97. The experimental prototype achieves high power factor and electrolytic capacitor-free, with the energy storage capacitor values ​​of 13.6μF and 53.8μF. When the voltage changes, the output current ripple remains basically unchanged and is controlled within 20%. Therefore, the size of the energy storage capacitor has little effect on the output current ripple. The energy storage capacitor uses a smaller capacity film capacitor instead of the electrolytic capacitor, thereby achieving electrolytic capacitor-free operation. After adding the auxiliary circuit, the voltage spike caused by the leakage inductance is better suppressed, thereby reducing the voltage stress of the switching tube; The main operating waveforms in the auxiliary energy storage capacitor discharge mode and charging mode, including the driving voltage of the main switch tube Q1 and the auxiliary switch tube Q2, the primary inductor current i p , secondary side inductor current i s , the current i flowing through the main switch tube Q1 Q1 The waveform of the main working waveform is consistent with the theory; The input and output power are determined by the instantaneous value of the input voltage and the effective value of the input voltage v rms Comparison is used to determine the output current; the output current is low-pass filtered and compared with the reference current, and then PI-adjusted and compared with the sawtooth wave to obtain the main switch tube single conduction drive signal; the average voltage of the auxiliary energy storage capacitor is low-pass filtered and compared with the energy storage capacitor set value, and then adjusted by PII and PIII to control the duty cycle coefficient k1 when the two switches are simultaneously turned on and the duty cycle coefficient k2 when they are simultaneously turned off. These are multiplied by the corresponding arrays and compared with the sawtooth wave to obtain the main switch tube and the auxiliary switch tube simultaneous conduction and simultaneous disconnection drive signals; In conjunction with the instructions Figure 8, the output current is selected as the variable to control the PFC function and constant current output of the variable control circuit, and the auxiliary energy storage capacitor voltage is selected as the variable to control the balance of the pulsating power difference. The output current io is sampled and compared with the current reference value Io-ref. After PI regulation, the duty cycle Dm is generated. The working mode of the circuit is judged by sampling the input voltage. When pin > Po, the working mode flag bit Pflag = 1; when pin < Po, the working mode flag bit Pflag = 0. The duty cycle coefficient Kcs is obtained by PI regulating the error between the auxiliary energy storage capacitor voltage Vcs(t) and the given reference value VCs_ref(t), and is multiplied by dp(t) and dn(t) respectively to obtain the actual duty cycles Dp(t) and Dn(t). According to the working mode flag bit Pflag, operations are performed on Dm, Dp(t), and Dn(t) to obtain the duty cycle of Q1. The digital control chip outputs PWM1 and PWM2 signals, and finally drives Q1 and Q2 through the drive circuit. The experimental waveforms of the input voltage vin, input current iin, auxiliary energy storage capacitor voltage sCv, and output current io after adding the auxiliary circuit are shown. It can be seen that the input current iin is a sine wave and is basically in phase with the input voltage vin after adding the auxiliary circuit. The circuit has a high power factor, and the output current is approximately a constant value, and the current ripple is only 12.43%. Combining with the attached instructions. Figure 9 , the input voltage is 85 - 135 V, and the relationship curves of the power factor and efficiency of the LED drive circuit with the input voltage. Throughout the input voltage range, the power factor remains above 0.990, and the efficiency at the rated input voltage is 81.07%. The auxiliary circuit absorbs pulsating power when pin > Po and releases pulsating power when pin < Po. The pulsating power undergoes two power conversions, which has a certain impact on the efficiency of the circuit. By appropriately reducing the pulsating power processed by the auxiliary circuit, the circuit efficiency is improved. The flyback converter and the auxiliary energy storage circuit are integrated, and the absorption and release of pulsating power by the auxiliary energy storage capacitor are controlled by adjusting the time when the two switching tubes are simultaneously off and simultaneously on, achieving the balance of input power and output power in the two modes of pin > Po and pin < Po. Compared with the traditional electrolytic-capacitor-free LED drive circuit, the two-switch electrolytic-capacitor-free LED drive circuit has fewer switching devices and a simpler control strategy. The experimental results show that when the auxiliary energy storage capacitor and the output filter capacitor are both 6.8 μF, the output current ripple coefficient is 10.43%, and the power factor reaches above 0.990, indicating that the circuit has a good low-frequency ripple suppression effect.

[0024] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A single-stage two-switch electrolytic capacitor-free LED driver circuit, comprising an electrolytic capacitor-free LED driver circuit, characterized in that: The electrolytic capacitor-free LED driving circuit includes an input voltage V in , Input rectifier diode VD r1 , Input rectifier diode VD r2 , Input rectifier diode VD r3 , Input rectifier diode VD r4 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o , output capacitor C o , energy storage element C a , switch tube Q2, auxiliary diode VD s , inductor L1, inductor L2, secondary side freewheeling diode VD p and input capacitor C in , one end of the input voltage Vin and the input rectifier diode VD r1 One end of the input rectifier diode VD is connected r1 The other end of the input rectifier diode VD r2 One end and the input capacitor C in one end of the .

2. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 1, characterized in that: The other end of the input voltage Vin is connected to the input rectifier diode VD r2 The other end and the input rectifier diode VD r4 One end of the input rectifier diode VD is connected r1 The other end of the input rectifier diode VD r3 One end of the input rectifier diode VD is connected r3 The other end and the input rectifier diode VD r4 The other end is connected to the input capacitor C in to the other end of the 3. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 1, characterized in that: The input capacitor C in The surface of the secondary side freewheeling diode VD p One end of the secondary freewheeling diode VD is connected p The other end is connected to one end of the inductor L1 and the transformer T r The other end of the inductor L1 is connected to one end of the switch tube Q1, and the inductor L1 is connected to the transformer T r One end of the inductor L2 is connected therebetween, and the other end of the inductor L2 is connected to one end of the switch tube Q2.

4. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 3, characterized in that: The connection between the inductor L1 and the switch tube Q1 is connected to the energy storage element C a One end of the switch tube Q2 is connected to the energy storage element C a The other end and the secondary side freewheeling diode VD o One end of the inductor L2 is connected to the auxiliary diode VD s one end of the .

5. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 4, characterized in that: The secondary side freewheeling diode VD o The other end and auxiliary diode VD s The other end of the output capacitor C o Connect both ends.

6. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 1, characterized in that: The energy storage element C a , switch tube Q1, switch tube Q2 and auxiliary diode VD s Form an auxiliary energy storage circuit.

7. The single-stage two-switch electrolytic capacitor-free LED driver circuit according to claim 1, characterized in that: The input rectifier diode VD r1 , Input rectifier diode VD r2 , Input rectifier diode VD r3 , Input rectifier diode VD r4 , diode VD p 、Transformer T r , switch tube Q1, secondary side freewheeling diode VD o and output capacitor C o Form a flyback converter.

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