A low output ripple electrolytic capacitor-free LED driver power supply and switching method

Abstract

The present invention discloses a low output ripple electrolytic capacitor-free LED driving power supply and a switching method, which belongs to the field of power electronics. The circuit topology includes: an AC power supply, an input filter inductor L f , input filter capacitor C f , bridge rectifier circuit, a Sepic circuit and a DC-DC converter circuit. It consists of a first switch tube Q1, a first inductor L1, a second inductor L2, a first diode D1, an intermediate energy storage capacitor C, and an output energy storage capacitor C B The Sepic circuit comprises a first switching transistor Q1, a second diode D2, a transformer T, an auxiliary capacitor C1, freewheeling diodes D3, D4, D5, and D6, an output filter inductor L0, an output filter capacitor C0, and an LED load, forming a DC-DC conversion circuit. The energy storage capacitor voltage of the present invention is designed to have a large pulsating ripple voltage, allowing the use of small-capacity non-electrolytic capacitors such as film capacitors instead of electrolytic capacitors. The Sepic circuit and the DC-DC conversion circuit share a single switching transistor, simplifying control and reducing switching losses.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics technology, and specifically relates to a low-output-ripple electrolytic-capacitor-free LED driving power supply and a switching method, which is applicable to switching power supplies and belongs to the field of alternating current / direct current (AC / DC) and direct current / direct current (DC / DC) converters. Background Art

[0002] Light-emitting diodes (LEDs) are a new generation of lighting sources. Their applications are rapidly increasing, offering advantages such as high luminous efficacy, long life, high reliability, compact size, and the absence of mercury. LEDs are used as light sources in lighting applications including street lighting, traffic lighting, automotive lighting, decorative lighting, and many others. The overall performance of LEDs depends heavily on the availability of a high-reliability, high power factor, long life, and low-cost driver.

[0003] In AC power supply, power factor correction is required to achieve a high power factor. When the input voltage and input current are ideal sinusoidal waves (i.e., with a power factor of 1), there is a ripple of Pocos²ωt between the instantaneous input and output power. To balance the instantaneous input and output power, traditional power supplies often use energy storage capacitors, typically electrolytic capacitors, to balance this power ripple. However, since the lifespan of electrolytic capacitors is only about one-tenth that of LEDs, they are a key component limiting the lifespan of LED power supplies. Therefore, to extend the lifespan of LED power supplies, it is essential to remove the electrolytic capacitors. Summary of the Invention

[0004] This invention addresses the issues of short lifespan, low transformer core utilization, and high output ripple in SEPIC-Flyback LED driver power supplies. By doing so, a low-output-ripple, electrolytic-capacitor-free LED driver power supply is proposed. This driver power supply circuit improves the flyback circuit into a forward-flyback circuit, enabling the DC-DC converter to operate in forward-flyback mode. This improves core utilization and reduces output ripple. Furthermore, thin-film capacitors replace electrolytic capacitors, thereby extending the lifespan of the LED driver power supply.

[0005] The technical solution of the circuit of the present invention is: a low output ripple electrolytic capacitor-free LED driving power supply, comprising an AC power supply, an input filter inductor L connected in sequence f , input filter capacitor C f, a bridge rectifier circuit, a Sepic circuit and an improved DC-DC conversion circuit; the improved DC-DC conversion circuit consists of a first switch tube Q1, a second diode D2, a transformer T, an auxiliary capacitor C1, freewheeling diodes D3, D4, D5, D6, an output filter inductor L0, an output filter capacitor C0 and an LED load; one end of the primary winding of the transformer T is connected to the cathode of the diode D2, and the other end of the primary winding of the transformer T is connected to the output energy storage capacitor C of the power factor correction unit (PFC) B The negative electrode of the output filter inductor L0 is connected to the anode of the freewheeling diode D3, and the other end of the output filter inductor L0 is connected to the anode of the freewheeling diode D4 and the negative electrode of the output filter capacitor C0.

[0006] Furthermore, the input filter inductor L f One end is connected to the positive pole of the AC power supply and the input filter inductor L f The other end is connected to the input filter capacitor C f Positive electrode, the filter capacitor C f The negative pole is connected to the negative pole of the AC power supply.

[0007] Furthermore, the bridge rectifier circuit is composed of a first diode Dr1, a second diode Dr2, a third diode Dr3 and a fourth diode Dr4; the anode of the first diode Dr1 is connected to the cathode of the fourth diode Dr4, the anode of the third diode Dr3 is connected to the cathode of the second diode Dr2, the first diode Dr1 is connected to the cathode of the third diode Dr3 and is connected to one end of the first inductor L1, and the second diode Dr2 is connected to the anode of the fourth diode Dr4 and is connected to the source of the first switching tube Q1 and the negative electrode of the intermediate energy storage capacitor C.

[0008] Furthermore, the Sepic circuit is composed of a first switch tube Q1, a first inductor L1, an output energy storage capacitor C B , the second inductor L2, the first diode D1, and the intermediate energy storage capacitor C; one end of the first inductor L1 is connected to the cathode of the first diode Dr1, and the other end of the first inductor L1 is connected to the output energy storage capacitor C B , the second inductor L2 and the drain of the first switching tube Q1, the drain of the first switching tube Q1 is connected to the anode of the second diode D2, the source of the first switching tube Q1 is connected to the negative electrode of the intermediate energy storage capacitor C and the anode of the second diode, and the anode of the intermediate energy storage capacitor C is connected to the second inductor and the cathode of the first diode D1.

[0009] Furthermore, the first inductor L1 operates in a current discontinuous mode to achieve an input power factor correction function.

[0010] Furthermore, current flows through the primary winding and the secondary winding of the transformer T during the on-time and off-time periods of the first switch tube Q1.

[0011] Furthermore, the intermediate energy storage capacitor C and the output energy storage capacitor C B The voltage is a DC voltage superimposed on a pulsating ripple voltage. Non-electrolytic capacitors with smaller capacitance are used instead of electrolytic capacitors.

[0012] A switching method for a low output ripple electrolytic capacitor-free LED driver power supply includes the following stages:

[0013] Working mode 1 [t0-t1]: At time t0, the first switch tube Q1 is turned on, the AC power supply charges the first inductor L1, the intermediate energy storage capacitor C charges the second inductor L2, and the output energy storage capacitor C B Part of the energy goes to the excitation inductor L m The other part of the energy is used to charge the output filter inductor L0, output filter capacitor C0 and LED load through transformer T and auxiliary capacitor C1;

[0014] Working mode 2 [t1-t2]: At time t1, the first switch tube Q1 is turned off, the AC power supply and the first inductor L1 together charge the intermediate energy storage capacitor C, and the second inductor L2 charges the output energy storage capacitor C. B Charging, excitation inductance L m The auxiliary capacitor C1 is charged through the transformer T. At the same time, the output filter inductor L0, the output filter capacitor C0, the freewheeling diodes D6 and D4 and the LED load form a freewheeling circuit. The output filter inductor L0 supplies power to the output filter capacitor C0 and the LED load.

[0015] Working mode 3 [t2-t3]: At t2, the first inductor L1 finishes discharging, the current of the inductor L2 continues to decrease, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, while the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6;

[0016] Working mode 4 [t3-t4]: At t3, the discharge of the second inductor L2 is completed, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, and the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6;

[0017] Working mode 5 [t4-t5]: At t4, the discharge of the filter inductor L0 is completed and the excitation inductor L mThe auxiliary capacitor C1 continues to be charged, and the output filter capacitor C0 and the LED load are powered through the flyback circuit.

[0018] Working mode 6 [t5-t6]: At t5, the excitation inductance L m After the discharge is completed, only the output filter capacitor C0 supplies power to the LED load.

[0019] Furthermore, the output energy storage capacitor C B The voltage of the intermediate energy storage capacitor C is a DC voltage superimposed on a pulsating ripple voltage, and a smaller-capacitance non-electrolytic capacitor is used instead of an electrolytic capacitor.

[0020] Furthermore, current flows through the primary winding and the secondary winding of the transformer T during the on-time and off-time periods of the first switch tube Q1.

[0021] The beneficial effects of the present invention are as follows: (1) a low output ripple electrolytic capacitor-free LED driver power supply, in which the energy storage capacitor voltage is designed to be in the form of a large pulsating ripple voltage, and a smaller capacitance non-electrolytic capacitor such as a film capacitor can be used instead of an electrolytic capacitor, thereby extending the service life of the LED driver power supply; (2) compared with the traditional flyback transformer, the improved forward flyback converter has a forward current flowing through the transformer during the on-state of the switch tube and a reverse current flowing through the transformer during the off-state of the switch tube, thereby realizing bidirectional excitation, improving the utilization rate of the magnetic core, and improving the efficiency of the LED driver power supply; (3) in the forward flyback mode, the output voltage and current ripple are small and the power factor is high; (4) the Sepic circuit and the DC-DC conversion circuit share a switch tube, which is simple to control and greatly reduces the switching loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of a low output ripple electrolytic capacitor-free LED driver power supply topology;

[0023] Figure 2 A schematic diagram of the main operating waveforms of a low output ripple electrolytic capacitor-free LED driver power supply circuit during one switching cycle;

[0024] Figure 3 Schematic diagram of the equivalent circuits of each switching mode of a low-output-ripple, electrolytic-capacitor-free LED driver circuit during a switching cycle. (a) is the equivalent circuit of mode 1; (b) is the equivalent circuit of mode 2; (c) is the equivalent circuit of mode 3; (d) is the equivalent circuit of mode 4; (e) is the equivalent circuit of mode 5; and (f) is the equivalent circuit of mode 6. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments of the present invention.

[0026] like Figure 1 As shown, the present invention provides a low output ripple electrolytic capacitor-free LED driver power supply, including an AC power supply, an input filter inductor L f , input filter capacitor C f , bridge rectifier circuit, first switch tube Q1, first inductor L1, second inductor L2, output energy storage capacitor C B , intermediate energy storage capacitor C, first diode D1, second diode D2, transformer T, auxiliary capacitor C1, freewheeling diodes D3, D4, D5, D6, output filter inductor L0, output filter capacitor C0 and LED load.

[0027] The bridge rectifier circuit consists of a first diode Dr1, a second diode Dr2, a third diode Dr3 and a fourth diode Dr4; the anode of the first diode Dr1 is connected to the cathode of the fourth diode Dr4, the anode of the third diode Dr3 is connected to the cathode of the second diode Dr2, the first diode Dr1 is connected to the cathode of the third diode Dr3 and is connected to one end of the first inductor L1, the second diode Dr2 is connected to the anode of the fourth diode Dr4 and is connected to the source of the first switching tube Q1 and the negative electrode of the intermediate energy storage capacitor C.

[0028] One end of the first inductor L1 is connected to the cathode of the first diode Dr1, and the other end of the first inductor L1 is connected to the output energy storage capacitor C B , the second inductor L2 and the drain of the first switching tube Q1, the drain of the first switching tube Q1 is connected to the anode of the second diode D2, the source of the first switching tube Q1 is connected to the negative electrode of the intermediate energy storage capacitor C and the anode of the second diode, and the anode of the intermediate energy storage capacitor C is connected to the second inductor and the cathode of the first diode D1.

[0029] One end of the primary winding of the transformer T is connected to the cathode of the diode D2, and the other end of the primary winding of the transformer T is connected to the PFC output capacitor C B The negative electrode of the freewheeling diode D3 is connected to the cathode of the freewheeling diode D4 and the anode of the freewheeling diode D5, the other end of the secondary winding of the transformer T is connected to the positive electrode of the auxiliary capacitor C1, the negative electrode of the auxiliary capacitor C1 is connected to the cathode of the freewheeling diode D3 and the anode of the freewheeling diode D6, one end of the output filter inductor L0 is connected to the anode of the freewheeling diode D3, and the other end of the output filter inductor L0 is connected to the anode of the freewheeling diode D4 and the negative electrode of the output filter capacitor C0.

[0030] The high-frequency switching frequency selected in the embodiment of the driving power circuit of the present invention is 120 kHz.

[0031] See also Figure 3 The equivalent circuits of the six operating modes of the driving power supply circuit of the present invention are given as follows:

[0032] Working mode 1 [t0-t1]: At time t0, the first switch tube Q1 is turned on, the AC power supply charges the first inductor L1, the intermediate energy storage capacitor C charges the second inductor L2, and the output energy storage capacitor C B Part of the energy goes to the excitation inductor L m The other part of the energy is used to charge the output filter inductor L0, output filter capacitor C0 and LED load through transformer T and auxiliary capacitor C1;

[0033] Working mode 2 [t1-t2]: At time t1, the first switch tube Q1 is turned off, the AC power supply and the first inductor L1 together charge the intermediate energy storage capacitor C, and the second inductor L2 charges the output energy storage capacitor C. B Charging, excitation inductance L m The auxiliary capacitor C1 is charged through the transformer T. At the same time, the output filter inductor L0, the output filter capacitor C0, the freewheeling diodes D6 and D4 and the LED load form a freewheeling circuit. The output filter inductor L0 supplies power to the output filter capacitor C0 and the LED load.

[0034] Working mode 3 [t2-t3]: At t2, the first inductor L1 finishes discharging, the current of the inductor L2 continues to decrease, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, while the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6;

[0035] Working mode 4 [t3-t4]: At t3, the discharge of the second inductor L2 is completed, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, and the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6;

[0036] Working mode 5 [t4-t5]: At t4, the discharge of the filter inductor L0 is completed and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, and the output filter capacitor C0 and the LED load are powered through the flyback circuit.

[0037] Working mode 6 [t5-t6]: At t5, the excitation inductance L m After the discharge is completed, only the output filter capacitor C0 supplies power to the LED load.

[0038] According to the above specific implementation scheme, the main output waveforms of the driving power circuit topology of the present invention are simulated.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, the technical solution of the present invention can be modified and replaced with equivalents without departing from the spirit and scope of the technical solution of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A low output ripple electrolytic capacitor-free LED driver power supply, characterized in that: Including the AC power supply, input filter inductor L connected in sequence f , input filter capacitor C f , a bridge rectifier circuit, a Sepic circuit and an improved DC-DC conversion circuit; the improved DC-DC conversion circuit consists of a first switch tube Q1, a second diode D2, a transformer T, an auxiliary capacitor C1, freewheeling diodes D3, D4, D5, D6, an output filter inductor L0, an output filter capacitor C0 and an LED load; one end of the primary winding of the transformer T is connected to the cathode of the diode D2, and the other end of the primary winding of the transformer T is connected to the output energy storage capacitor C of the power factor correction unit (PFC) B and the positive electrode of the first diode D1, one end of the secondary winding of the transformer T is connected to the cathode of the freewheeling diode D4 and the anode of the freewheeling diode D5, the other end of the secondary winding of the transformer T is connected to the positive electrode of the auxiliary capacitor C1, the negative electrode of the auxiliary capacitor C1 is connected to the cathode of the freewheeling diode D3 and the anode of the freewheeling diode D6, one end of the output filter inductor L0 is connected to the anode of the freewheeling diode D3, and the other end of the output filter inductor L0 is connected to the anode of the freewheeling diode D4 and the negative electrode of the output filter capacitor C0; The first inductor L1 operates in a current discontinuous mode to achieve input power factor correction function; Current flows through the primary winding and the secondary winding of the transformer T during the on and off periods of the first switch tube Q1; Intermediate energy storage capacitor C and output energy storage capacitor C B The voltage is a DC voltage superimposed on a pulsating ripple voltage. Non-electrolytic capacitors with smaller capacitance are used instead of electrolytic capacitors.

2. The low output ripple electrolytic capacitor-free LED driver power supply according to claim 1, characterized in that: The input filter inductor L f One end is connected to the positive pole of the AC power supply and the input filter inductor L f The other end is connected to the input filter capacitor C f Positive electrode, the filter capacitor C f The negative pole is connected to the negative pole of the AC power supply.

3. The low output ripple electrolytic capacitor-free LED driver power supply according to claim 1, characterized in that: The bridge rectifier circuit consists of a first diode Dr1, a second diode Dr2, a third diode Dr3 and a fourth diode Dr4; the anode of the first diode Dr1 is connected to the cathode of the fourth diode Dr4, the anode of the third diode Dr3 is connected to the cathode of the second diode Dr2, the first diode Dr1 is connected to the cathode of the third diode Dr3 and is connected to one end of the first inductor L1, the second diode Dr2 is connected to the anode of the fourth diode Dr4 and is connected to the source of the first switching tube Q1 and the negative electrode of the intermediate energy storage capacitor C.

4. The low output ripple electrolytic capacitor-free LED driver power supply according to claim 1, characterized in that: The Sepic circuit consists of a first switch tube Q1, a first inductor L1, and an output energy storage capacitor C B , the second inductor L2, the first diode D1, and the intermediate energy storage capacitor C; one end of the first inductor L1 is connected to the cathode of the first diode Dr1, and the other end of the first inductor L1 is connected to the output energy storage capacitor C B , the second inductor L2 and the drain of the first switching tube Q1, the drain of the first switching tube Q1 is connected to the anode of the second diode D2, the source of the first switching tube Q1 is connected to the negative electrode of the intermediate energy storage capacitor C and the anode of the second diode, and the anode of the intermediate energy storage capacitor C is connected to the second inductor and the cathode of the first diode D1.

5. A switching method for a low output ripple electrolytic capacitor-free LED driver power supply, characterized in that: The following stages are included: Working mode 1 [t0-t1]: At time t0, the first switch tube Q1 is turned on, the AC power supply charges the first inductor L1, the intermediate energy storage capacitor C charges the second inductor L2, and the output energy storage capacitor C B Part of the energy goes to the excitation inductor L m The other part of the energy is used to charge the output filter inductor L0, output filter capacitor C0 and LED load through transformer T and auxiliary capacitor C1; Working mode 2 [t1-t2]: At time t1, the first switch tube Q1 is turned off, the AC power supply and the first inductor L1 together charge the intermediate energy storage capacitor C, and the second inductor L2 charges the output energy storage capacitor C. B Charging, excitation inductance L m The auxiliary capacitor C1 is charged through the transformer T. At the same time, the output filter inductor L0, the output filter capacitor C0, the freewheeling diodes D6 and D4 and the LED load form a freewheeling circuit. The output filter inductor L0 supplies power to the output filter capacitor C0 and the LED load. Working mode 3 [t2-t3]: At t2, the first inductor L1 finishes discharging, the current of the inductor L2 continues to decrease, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, while the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6; Working mode 4 [t3-t4]: At t3, the discharge of the second inductor L2 is completed, and the excitation inductor L m The auxiliary capacitor C1 continues to be charged, and the output filter inductor L0 continues to supply power to the output filter capacitor C0 and the LED load through the freewheeling diodes D3 and D6; Working mode 5 [t4-t5]: At t4, the discharge of the filter inductor L0 is completed and the excitation inductor L m Continue to charge the auxiliary capacitor C1, and supply power to the output filter capacitor C0 and LED load through the flyback circuit; Working mode 6 [t5-t6]: At t5, the excitation inductance L m After the discharge is completed, only the output filter capacitor C0 supplies power to the LED load.

6. The switching method of a low output ripple electrolytic capacitor-free LED driving power supply according to claim 5, characterized in that: The output energy storage capacitor C B The voltage of the intermediate energy storage capacitor C is a DC voltage superimposed on a pulsating ripple voltage, and a smaller-capacitance non-electrolytic capacitor is used instead of an electrolytic capacitor.

7. The switching method of a low output ripple electrolytic capacitor-free LED driving power supply according to claim 6, characterized in that: Current flows through the primary winding and the secondary winding of the transformer T during the on-time and off-time periods of the first switch tube Q1.

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