Drain feedback and source feedback combined forced resonance flyback constant current power supply

Abstract

The invention provides a drain feedback and source feedback combined forced resonance flyback constant current power supply, which relates to the technical field of switching power supplies and comprises a transformer T1, an RCD clamping circuit, a first switching tube Q1, a second switching tube Q2 and a control circuit, and the control circuit is used for providing a first control signal and a second control signal to respectively control the switching state of the first switching tube and the switching state of the second switching tube so as to realize zero-voltage conduction of the first switching tube. Through the characteristic of the forced resonance auxiliary circuit, the characteristic of soft switching of the first switching tube is realized, and the switching loss is greatly reduced; meanwhile, the mode of combining drain electrode feedback and source electrode feedback is used, the size of the converter is reduced, the production cost is reduced, and the sampling precision is improved.

Description

Technical Field

[0001] The invention relates to the technical field of switching power supplies, in particular to a forced resonance flyback constant current power supply combining drain feedback and source feedback. Background Art

[0002] With the rapid development of electronic information technology, miniaturized and integrated electronic devices emerge in an endless stream. Electronic devices in the fields of Internet of Things, industrial electronics, automotive electronics, etc. are full of opportunities and challenges, which makes the research of power management technology receive widespread attention in the field of integrated circuits. The switching power supply controls the periodic conduction and shutdown of the power switch tube in the system, thereby controlling the transmission and conversion process of energy to adjust the output voltage value, and has significant application advantages such as small size, low power consumption, high efficiency, and wide adjustment range. In power applications below 100W, compared with various common switching power supply topologies, the flyback converter uses fewer components, has a simple structure, low cost, good transient response, and can achieve electrical isolation between the input and output ends, so it has been widely used.

[0003] For flyback converters under high-frequency operation, snubber circuit loss, switching loss and transformer loss are the three main sources of loss. Among them, the proportion of switching loss of the primary main switch tube of the flyback switching power supply is proportional to the operating frequency, which seriously affects the high-frequency and high-efficiency of the flyback switching power supply. Therefore, it is particularly important to significantly reduce the switching loss of the primary main switch tube of the flyback converter. In the flyback converter, although the primary side regulator (PSR) flyback converter has made great progress, it still has some defects: due to the indirect feedback method, the regulation effect is affected by the real-time changes of the load and component temperature and the batch tolerance; the feedback voltage obtained by sampling the auxiliary winding includes the output voltage and the voltage division of the freewheeling diode, and it is difficult to obtain an accurate output voltage; and PSR feedback requires a transformer auxiliary winding, which increases the production cost. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a forced resonant flyback constant current power supply combining drain feedback and source feedback. Based on the flyback topology, through a newly added forced resonant auxiliary winding, a reverse excitation current can be generated on the primary side after the demagnetization of the secondary side of the transformer is completed and before the main switch tube is turned on, so that the excitation inductance resonates with the parasitic capacitance of the primary main switch tube, and the charge of the drain-source capacitance of the primary main switch tube is emptied to achieve zero voltage turn-on of the main switch tube in DCM mode, thereby improving the switching loss of the constant current power supply; at the same time, a combination of drain feedback and source feedback is used to control the power supply voltage and current respectively, and the sampling auxiliary winding is omitted while realizing dual-loop control, thereby reducing the size of the converter, reducing production costs, and improving sampling accuracy.

[0005] To achieve the above object, the present invention provides the following technical solutions: A forced resonant flyback constant current power supply combining drain feedback and source feedback, comprising a transformer T1, wherein the transformer T1 comprises a primary winding L1, a forced resonant auxiliary winding L2, and a secondary winding L3; The same-name end of the primary winding L1 is connected to the positive electrode of the DC power supply, the opposite-name end of the primary winding L1 is connected to the input end of the first switch tube Q1, and the output end of the first switch tube Q1 is connected to the input reference ground through the resistor R2; The same-name end of the forced resonant auxiliary winding L2 is connected to the drain of the second switch tube Q2, the opposite-name end of the forced resonant auxiliary winding L2 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the source of the second switch tube and the input reference ground; The cathode of the second diode D2 is connected to the same-name end of the secondary winding L3, and the anode of the diode D2 is connected to the third capacitor C3, one end of the load resistor R3 and the reference ground of the output; Furthermore, a forced resonant flyback constant current power supply combining drain feedback and source feedback also includes an RCD clamping circuit, wherein the clamping circuit includes a diode D1, a capacitor C1, and a resistor R1: The cathode of the first diode D1 is connected to the first capacitor C1 and one end of the first resistor R1, and the anode of the diode D2 is connected to the drain of the first switch tube Q1 and the opposite end of the primary winding L1 of the transformer T1; The other ends of the first resistor R1 and the first capacitor C1 are connected to the positive electrode of the DC power supply and the same-name end of the primary winding of the transformer T1; The control circuit is used to provide a first control signal and a second control signal to control the switching states of the first switch tube Q1 and the second switch tube Q2 respectively, so as to realize zero voltage conduction of the first switch tube Q1.

[0006] Furthermore, a forced resonant flyback constant current power supply combining drain feedback and source feedback, the control circuit includes: A sampling unit, used for indirectly sampling the voltage and current signals output by the forced resonant flyback constant current power supply combining drain feedback and source feedback at the drain-source of the first switch tube Q1; A feedback unit, which adjusts according to the signal obtained by the sampling unit to obtain a compensation signal; The driving unit generates a first control signal and a second control signal according to the compensation signal obtained by the feedback unit.

[0007] Furthermore, a forced resonant flyback constant current power supply combining drain feedback and source feedback, the sampling unit includes: A current sampling unit, used for sampling the input current of the forced resonant flyback constant current power supply combining drain feedback and source feedback and the source current of the first switch tube Q1; The voltage sampling unit is used to sample the input voltage of the forced resonant flyback constant current power supply combining drain feedback and source feedback and the drain voltage of the first switch tube Q1.

[0008] Furthermore, a forced resonant flyback constant current power supply combining drain feedback and source feedback, the feedback unit includes: An isolated feedback device, used for feeding back the output of the current and voltage sampling units to the main controller, wherein the input end thereof is respectively connected to the output end of the current sampling unit and the output end of the voltage sampling unit, and the output end thereof is connected to the positive input end of the first adder; The compensation signal generating unit is used to adjust the signal fed back by the isolated feedback device and then output it to the driving unit to obtain a PWM signal for adjusting the switch tube.

[0009] Furthermore, in a forced resonant flyback constant current power supply combining drain feedback and source feedback, the compensation signal generating unit includes: A current reference unit, a first adder, a current outer loop PI regulator, a first limiter, a voltage reference unit, a second adder, a voltage inner loop PI regulator, and a second limiter; Among them, the current feedback signal is connected to the positive input terminal of the first adder, the current reference unit is connected to the negative input terminal of the first adder, the output terminal of the first adder is connected to the input terminal of the current outer loop PI regulator, the output terminal of the current outer loop PI regulator is connected to the input terminal of the first limiter, the output terminal of the first limiter is connected to the positive input terminal of the second adder, the voltage reference unit is connected to the negative input terminal of the second adder, the output terminal of the second adder is connected to the input terminal of the voltage inner loop PI regulator, and the output of the voltage inner loop PI regulator is connected to the input terminal of the second limiter.

[0010] Furthermore, in a forced resonant flyback constant current power supply combining drain feedback and source feedback, the driving unit includes: A driving signal generating unit, used to generate the first control signal and the second control signal to control the switching states of the first switch tube Q1 and the second switch tube Q2; The PWM driving unit converts the first control signal and the second control signal generated by the driving signal generating unit into a PWM signal that can control the switching state of the switch tube.

[0011] Furthermore, in a forced resonant flyback constant current power supply combining drain feedback and source feedback, the drive signal generating unit includes: Sawtooth wave generator, a first comparator, a second comparator, and a logic signal delay device; Among them, the positive input end of the first comparator is connected to the output end of the limiter, the negative input end of the first comparator is connected to the output end of the sawtooth wave generator, the output end of the first comparator is connected to the gate of the first switching tube, the positive input end of the second comparator is connected to the duty cycle signal of the second switching tube, the negative input end of the second comparator is connected to the output end of the sawtooth wave generator, the output end of the second comparator is connected to the input of the logic signal delayer, and the output end of the logic signal delayer is connected to the gate of the second switching tube.

[0012] Furthermore, in a forced resonant flyback constant current power supply combining drain feedback and source feedback, the gate drive voltage of the first and second switch tubes in the PWM drive unit is 5V when they are turned on, and the gate drive voltage of the first and second switch tubes is 0V when they are turned off.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention replaces the primary main switch tube in the flyback constant current power supply with a GaN HEMT, and utilizes the characteristics of low on-resistance and low charging capacitance of the GaN HEMT to achieve high speed, high frequency and miniaturization of the flyback switch constant current power supply.

[0015] 2. In the embodiment of the present invention, the forced resonant flyback constant current power supply combining drain feedback and source feedback realizes zero voltage conduction of the main switch tube through the forced resonant auxiliary winding in the discontinuous conduction mode of the excitation inductor current, which greatly reduces the conduction loss of the main switch tube and realizes high efficiency of the power supply.

[0016] 3. The forced resonant flyback constant current power supply combining drain feedback and source feedback in the embodiment of the present invention uses drain feedback voltage and source feedback current to eliminate the sampling auxiliary winding, eliminate the need to use temperature-restricted devices such as optocouplers, and further reduce the size of the power supply.

[0017] 4. The forced resonant flyback constant current power supply combining drain feedback and source feedback in the embodiment of the present invention uses a dual-loop PI regulator with an inner voltage loop and an outer current loop to achieve constant current output while ensuring that the voltage output is within a fixed range, and has the advantages of low current ripple and high output current accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a schematic diagram of the overall structure of a forced resonant flyback constant current power supply combining drain feedback and source feedback according to the present invention.

[0019] Figure 2 The present invention is an indirect sampling principle diagram of a forced resonant flyback constant current power supply combining drain feedback and source feedback.

[0020] Figure 3 The present invention is a schematic diagram of a feedback unit of a forced resonant flyback constant current power supply combining drain feedback and source feedback.

[0021] Figure 4 The present invention is a schematic diagram of a driving signal generating unit of a forced resonant flyback constant current power supply combining drain feedback and source feedback.

[0022] Figure 5 The present invention discloses a single-cycle driving signal timing diagram of a forced resonant flyback constant current power supply combining drain feedback and source feedback and a waveform diagram corresponding to zero-voltage conduction of a first switch tube.

[0023] Figure 6 The output current PSIM simulation waveform diagram of the forced resonant flyback constant current power supply combining drain feedback and source feedback of the present invention when the current outer loop is in effect.

[0024] Figure 7 The output voltage PSIM simulation waveform diagram of the forced resonant flyback constant current power supply combining drain feedback and source feedback of the present invention when the voltage inner loop is in effect. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described in more detail below with reference to the relevant drawings. The drawings provide embodiments of the present invention, but the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0026] like Figure 1 As shown, the forced resonant flyback constant current power supply combining drain feedback and source feedback in the example of the present invention includes: a DC power supply, a transformer T1, a first switch tube Q1, a second switch tube Q2, a first resistor R1, a first capacitor C1, a first diode D1, a second resistor R2, a second capacitor C2, a second diode D2, a third capacitor C3, a load resistor R3 and a control circuit.

[0027] The DC power supply VDC is used to power the entire circuit. Its positive electrode is connected to the same-name end of the first capacitor C1, the first resistor R1, and the primary winding L1 of the transformer T1. The cathode of the first diode D1 is connected to the first capacitor C1 and the other end of the first resistor R1 to form an RCD clamping circuit, which is used to eliminate the voltage spike generated when the first switch tube Q1 is turned off and absorb the excess energy on the transformer leakage inductance to protect the switch tube. The opposite-name end of the primary winding L1 of the transformer T1 is connected to the anode of the first diode D1 and the drain of the first switch tube Q1. The source of the first switch tube Q1 is connected to the second resistor R2 and the control circuit. The voltage across the second resistor R2 is measured to calculate the input current. The drain of the first switch tube Q1 is connected to the control circuit to indirectly sample the power supply output voltage.

[0028] The drain of the second switch tube Q2 is connected to the same-name end of the forced resonance auxiliary winding, and the source is connected to one end of the second capacitor C2 and the input reference ground. Compared with the traditional flyback topology circuit, the auxiliary winding is added to generate a reverse excitation current to drain the charge on the parasitic capacitance of the first switch tube when the transformer excitation inductance Lm and the parasitic capacitance of the first switch tube spontaneously resonate after the first switch tube is turned off and the secondary side is demagnetized, so as to achieve zero voltage conduction. The first switch tube and the second switch tube are both GaN HEMTs, which are used to achieve higher switching frequency, faster switching speed and smaller on-resistance.

[0029] The cathode of the second diode D2 on the secondary side of the transformer is connected to the same-name end of the secondary winding, and the anode is connected to the third capacitor C3, one end of the load resistor R3 and the output reference ground, and the secondary side of the transformer outputs a voltage Vo to the load resistor R3.

[0030] The control circuit is used to provide a first control signal and a second control signal to control the switch states of the first switch tube Q1 and the second switch tube Q2 respectively. The control circuit includes: a sampling unit, a feedback unit, and a driving unit. The sampling unit is respectively connected to the drain and source of the first switch tube Q1 and is used to indirectly sample the output voltage and output current of the power supply. The sampled voltage and current signals are output to the feedback unit, and are adjusted according to the signal obtained by the sampling unit to obtain a compensation signal, and finally the first control signal and the second control signal are generated according to the compensation signal obtained by the feedback unit.

[0031] The indirect sampling principle of the forced resonant flyback constant current power supply combining drain feedback and source feedback is as follows: Figure 2 As shown, the primary current Ip reaches its maximum value when the first switch tube Q1 is turned off. In formula (1), There will be slight changes under different working conditions, but this change is small. The switching period T is also fixed in PWM mode. The demagnetization time can be obtained by using the inflection point detection method for the drain voltage Vd of the first switch tube Q1. At this time, the output current Io, i.e. the source feedback current, can be calculated by sampling the primary peak current at the source of the first switch tube Q1. In formula (2), the DC input power supply VDC and the turns ratio At this time, the output voltage Vo, that is, the drain feedback voltage, can be calculated by sampling the drain voltage Vd of the first switch tube Q1 at the end of the secondary side demagnetization.

[0032]

[0033]

[0034] The schematic diagram of the feedback unit of the forced resonant flyback constant current power supply combining drain feedback and source feedback is as follows: Figure 3 As shown, after the current and voltage signals are collected by the sampling unit, they are output to the isolation feedback device in the feedback unit to achieve electrical isolation. Wherein, the reference unit is connected to the positive input end of the adder, the output end of the adder is connected to the input end of the current outer loop PI regulator, the output end of the current outer loop PI regulator is connected to the input end of the voltage inner loop PI regulator, the output of the voltage inner loop PI regulator is connected to the input end of the limiter, and the compensation signal is output by the limiter. Wherein, the PI regulator is used to generate the compensation signal, and the limiter is used to limit the size of the compensation signal to ensure that the forced resonant flyback constant current power supply can operate normally.

[0035] The schematic diagram of the driving signal generating unit of the forced resonant flyback constant current power supply combining drain feedback and source feedback is as follows: Figure 4As shown, it is used to convert the compensation signal obtained by the feedback unit into a first control signal and a second control signal, and the two control signals are both PWM signals, and they will not be high at the same time in the same cycle, wherein the positive input end of the first comparator is connected to the output end of the limiter, the negative input end of the first comparator is connected to the output end of the sawtooth wave generator, the output end of the first comparator is connected to the gate of the first switch tube, the positive input end of the second comparator is connected to the duty cycle signal of the second switch tube, the negative input end of the second comparator is connected to the output end of the sawtooth wave generator, the output end of the second comparator is connected to the input of the logic signal delayer, and the output end of the logic signal delayer is connected to the gate of the second switch tube. Wherein, the sawtooth wave generator is used as a carrier to generate a PWM signal, which is compared with the compensation signal after limiting, and the part higher than the compensation signal outputs a low level, and the part lower than the compensation signal outputs a high level, thereby obtaining a PWM signal with a duty cycle corresponding to the amplitude of the compensation signal. Similarly, the carrier of the PWM signal generated by the sawtooth wave generator is compared with the duty cycle signal D of the second switch tube to obtain the PWM signal of the second switch tube. After passing through the logic signal delayer, the second control signal is generated in the spontaneous resonance stage after the secondary side demagnetization is completed to drive the second switch tube, and there is a dead time t between the second control signal and the first control signal. dead Among them, the second switch duty cycle signal D and the dead time t dead Depends on the output power.

[0036] The single-cycle driving timing signal of the forced resonant flyback constant current power supply combining drain feedback and source feedback and the corresponding zero voltage turn-on waveform of the first switch tube are shown in the figure. Figure 5As shown, the first control signal is used to control the first switch tube Q1. When Q1 is turned on, the DC power supply VDC charges the excitation inductance and leakage inductance of the transformer T1, the second switch tube Q2 is in the off state, the second diode D2 is in the off state, and no current flows through the secondary winding. When the first switch tube Q1 is turned off, the excitation inductance begins to discharge, the same-name end of the transformer is reversed, the second diode on the secondary side is turned on and current flows; at this time, the second switch tube is still in the off state, and due to the reverse conduction characteristics of the GaN HEMT, the resonant winding L3 is forced to charge the capacitor C2. Since the power supply works in the DCM mode, the excitation inductance discharge ends before the single cycle ends, the secondary current is 0, the second diode D2 is turned off, and the transformer enters the spontaneous resonance stage. At this time, the second control signal is used to control the second switch tube Q2. When Q2 is turned on, the first switch tube Q1 is in the off state and the second diode D2 is cut off. The second capacitor C2 discharges to the forced resonant winding L2 and the voltage across L2 is clamped. When Q2 is turned off, the same-name end of the transformer is reversed again, and the primary winding L1 is reversely excited. During the dead time, the remaining charge on the drain-source parasitic capacitance of the first switch tube Q1 is evacuated to achieve zero voltage conduction of the first switch tube Q1. This process can be regarded as the resonance of L1 and the drain-source parasitic capacitance of the switch tube Q1. The forced resonant flyback constant current power supply combining drain feedback and source feedback has greatly improved the problem of switch conduction loss.

[0037] The above implementation modes are merely exemplary descriptions of the present invention and do not limit its protection scope. Those skilled in the art may also make partial changes thereto and may change the selection of the regulator according to actual conditions to generate a better compensation signal. Any form of equivalent replacement that conforms to the spirit of the invention falls within the protection scope of the present invention.

Claims

1. A forced resonant flyback constant current power supply combining drain feedback and source feedback, characterized in that: include: It includes a transformer T1, an RCD clamping circuit, a first switch tube Q1, a second switch tube Q2 and a control circuit; The transformer T1 includes a primary winding L1, a forced resonance auxiliary winding L2, and a secondary winding L3; The same-name end of the primary winding L1 is connected to the positive electrode of the DC power supply, the opposite-name end of the primary winding L1 is connected to the input end of the first switch tube Q1, and the output end of the first switch tube Q1 is connected to the input reference ground through the resistor R2; The same-name end of the forced resonant auxiliary winding L2 is connected to the drain of the second switch tube Q2, the opposite-name end of the forced resonant auxiliary winding L2 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the source of the second switch tube and the input reference ground; The cathode of the second diode D2 is connected to the same-name end of the secondary winding L3, and the anode of the diode D2 is connected to the third capacitor C3, one end of the load resistor R3 and the reference ground of the output; The cathode of the first diode D1 is connected to the first capacitor C1 and one end of the first resistor R1, and the anode of the diode D2 is connected to the drain of the first switch tube Q1 and the opposite end of the primary winding L1 of the transformer T1; The other ends of the first resistor R1 and the first capacitor C1 are connected to the positive electrode of the DC power supply and the same-name end of the primary winding L1 of the transformer T1; The control circuit is used to provide a first control signal and a second control signal to control the switching states of the first switch tube Q1 and the second switch tube Q2 respectively, so as to realize zero voltage conduction of the first switch tube Q1, wherein the control circuit includes: A sampling unit, used for indirectly sampling the voltage and current signals output by the forced resonant flyback constant current power supply combining drain feedback and source feedback at the drain-source of the first switch tube Q1; A feedback unit, which adjusts according to the signal obtained by the sampling unit to obtain a compensation signal; The driving unit generates a first control signal and a second control signal according to the compensation signal obtained by the feedback unit.

2. According to claim 1, the forced resonant flyback constant current power supply combining drain feedback and source feedback is characterized in that: The first switch tube Q1 and the second switch tube Q2 must be gallium nitride (GaN) high electron mobility transistors (HEMTs) to achieve high frequency, high efficiency and miniaturization of the forced resonance flyback constant current power supply.

3. The forced resonant flyback constant current power supply combining drain feedback and source feedback according to claim 1, characterized in that: The sampling unit of the control circuit comprises: A current sampling unit, used for sampling the input current of the forced resonant flyback constant current power supply combining drain feedback and source feedback and the source current of the first switch tube Q1; The voltage sampling unit is used to sample the input voltage of the forced resonant flyback constant current power supply combining drain feedback and source feedback and the drain voltage of the first switch tube Q1.

4. According to claim 1, the forced resonant flyback constant current power supply combining drain feedback and source feedback is characterized in that: The feedback unit of the control circuit comprises: An isolated feedback device, used for feeding back the output of the current and voltage sampling units to the main controller, wherein the input end thereof is respectively connected to the output end of the current sampling unit and the output end of the voltage sampling unit, and the output end thereof is connected to the positive input end of the first adder; The compensation signal generating unit is used to adjust the signal fed back by the isolated feedback device and then output it to the driving unit to obtain a PWM signal for adjusting the switch tube.

5. The forced resonant flyback constant current power supply combining drain feedback and source feedback according to claim 1, characterized in that: The driving unit of the control circuit comprises: A driving signal generating unit, used to generate the first control signal and the second control signal to control the switching states of the first switch tube Q1 and the second switch tube Q2; The PWM driving unit converts the first control signal and the second control signal generated by the driving signal generating unit into a PWM signal that can control the switching state of the switch tube, wherein the gate driving voltage when the first and second switch tubes are turned on is 5V, and the gate driving voltage when the first and second switch tubes are turned off is 0V.

6. The forced resonant flyback constant current power supply combining drain feedback and source feedback according to claim 4, characterized in that: The compensation signal generating unit comprises: a current reference unit, a first adder, a current outer loop PI regulator, a first limiter, a voltage reference unit, a second adder, a voltage inner loop PI regulator, and a second limiter; Among them, the current feedback signal is connected to the positive input terminal of the first adder, the current reference unit is connected to the negative input terminal of the first adder, the output terminal of the first adder is connected to the input terminal of the current outer loop PI regulator, the output terminal of the current outer loop PI regulator is connected to the input terminal of the first limiter, the output terminal of the first limiter is connected to the positive input terminal of the second adder, the voltage reference unit is connected to the negative input terminal of the second adder, the output terminal of the second adder is connected to the input terminal of the voltage inner loop PI regulator, and the output of the voltage inner loop PI regulator is connected to the input terminal of the second limiter.

7. The forced resonant flyback constant current power supply combining drain feedback and source feedback according to claim 5, characterized in that: The driving signal generating unit comprises: a sawtooth wave generator, a first comparator, a second comparator, and a logic signal delay device; Among them, the positive input end of the first comparator is connected to the output end of the limiter, the negative input end of the first comparator is connected to the output end of the sawtooth wave generator, the output end of the first comparator is connected to the gate of the first switching tube, the positive input end of the second comparator is connected to the duty cycle signal of the second switching tube, the negative input end of the second comparator is connected to the output end of the sawtooth wave generator, the output end of the second comparator is connected to the input of the logic signal delayer, and the output end of the logic signal delayer is connected to the gate of the second switching tube.

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