Self-powered circuit of switching power supply and switching power supply

Abstract

The invention provides a self-powered circuit of a switching power supply and the switching power supply, and the self-powered circuit comprises a power supply capacitor which is used for generating a power supply voltage to supply power to a control chip of the switching power supply; the first linear voltage stabilizing circuit is connected between the power supply capacitor and the main power tube, and in the starting process of the switching power supply, the first linear voltage stabilizing circuit is switched on, and the power supply capacitor is charged; the second linear voltage stabilizing circuit is connected with the first linear voltage stabilizing circuit in parallel, when the power supply voltage reaches a first threshold value, the switching power supply is started, and when the PWM signal is effective, the second linear voltage stabilizing circuit is switched on, the main power tube is switched off, and the power supply capacitor is charged until the power supply voltage reaches a second threshold value; the second threshold value is greater than the first threshold value. The power consumption can be saved, and the working efficiency of the switching power supply is improved.

Description

Technical Field

[0001] The invention relates to the field of power electronics, and in particular to a self-powered circuit of a switching power supply and a switching power supply. Background Art

[0002] By using normally on power devices, self-starting and self-powering can be realized more conveniently. The self-starting function can save the need for additional resistor starting or high-voltage starting circuits, and the self-powering function can save the need for auxiliary winding power supply.

[0003] like Figure 1 As shown, it is a self-powered circuit of a switching power supply of the prior art. The switching power supply takes a flyback converter as an example. The self-powered circuit includes a main power tube Q1 and an auxiliary power tube Q2 connected in series. A diode D1 is connected between the common connection end and the power supply capacitor C0. A power supply voltage VDD is generated on the power supply capacitor C0. The power supply voltage VDD is used to power the control chip of the switching power supply. The power supply voltage VDD passes through the LDO (linear regulation circuit) to obtain a voltage VCC, which is used to power the drive circuit 01 of the auxiliary power tube Q2. The drive circuit 01 receives a PWM signal to generate a drive signal DRV for controlling the on and off of the auxiliary power tube Q2. The signal waveform of the self-powered circuit is shown in FIG. Figure 2 As shown, during the conduction period of the main power tube Q1 and the auxiliary power tube Q2 (t1-t2), the magnetizing inductor of the flyback converter stores energy, the inductor current I_Lm rises, the voltage Vsw at SW and the voltage drop Vds_Q2 across the auxiliary power tube Q2 are low, the control chip is powered by the power supply voltage VDD, and the VDD voltage drops. During the shutdown period of the main power tube Q1 and the auxiliary power tube Q2 (t2-t3), the magnetizing inductor current supplies power to the output, the inductor current I_Lm drops, and the voltage Vsw at SW is clamped to Vin+Nps*Vo, where Vin is the DC input voltage of the flyback converter, Vo is the output voltage, and Nps is the primary-to-secondary turns ratio of the transformer Nps=Np / Ns. At this time, the main power tube Q1 operates in the linear region, the C0 capacitor is charged, and the voltage drop of the main power tube Q1 is Vds_Q1=V SW -(-Vgs_th), where Vgs_th is the threshold voltage of the D-Mode power device. Since the voltage at SW is clamped, the loss of the main power tube Q1 is relatively large, and the loss P = Vds_Q1*Ivdd, where Ivdd is the average current consumed by the chip.

[0004] When the main power tube Q1 and the auxiliary power tube Q2 are turned off, the power supply voltage VDD comes from the voltage Vsw at SW. Vsw is a high voltage. At this time, the main power tube Q1 works in the linear region, similar to a high-voltage LDO, which will cause large power supply loss and low system efficiency. Summary of the invention

[0005] The object of the present invention is to provide a self-powered circuit of an efficient switching power supply and a switching power supply, so as to solve the problems of large power supply loss and low system efficiency in the prior art.

[0006] The present invention also provides a self-powered circuit of a switching power supply, the switching power supply comprising a main power tube, an auxiliary power tube and an inductor, the inductor is connected to a first end of the main power tube, the auxiliary power tube is connected between a second end of the main power tube and a ground end, and comprises:

[0007] A power supply capacitor, a first end of which is connected to the power supply end of the control chip of the switching power supply, a second end of which is grounded, and a first end of which generates a power supply voltage;

[0008] A first linear voltage stabilizing circuit, connected between the first end of the power supply capacitor and the common connection end of the main power tube and the auxiliary power tube;

[0009] A second linear voltage stabilizing circuit, connected in parallel with the first linear voltage stabilizing circuit;

[0010] Among them, during the startup of the switching power supply, the first linear voltage regulator circuit is turned on and the power supply capacitor is charged; when the PWM signal generated by the control chip of the switching power supply is valid, the second linear voltage regulator circuit is turned on and the power supply capacitor is charged.

[0011] Optionally, when the PWM signal is valid, after the main power tube is turned on for a period of time, the second linear voltage regulation circuit is turned on and the auxiliary power tube is turned off.

[0012] Optionally, when the PWM signal changes from invalid to valid, the second linear voltage regulator circuit is turned on and the auxiliary power tube is turned off.

[0013] Optionally, when the supply voltage reaches a first threshold, the first linear voltage regulation circuit is turned off.

[0014] Optionally, when the supply voltage reaches a second threshold, the second linear voltage regulator circuit is turned off and the auxiliary power tube is turned on.

[0015] Optionally, when the conduction time of the second linear voltage regulator circuit reaches a set time, the second linear voltage regulator circuit is turned off and the auxiliary power tube is turned on.

[0016] Optionally, the first linear voltage stabilization circuit includes a first capacitor, a first diode and a linear adjustment unit, the anode of the first diode is connected to the main power tube, the cathode of the first diode is connected to the first end of the first capacitor, the second end of the first capacitor is grounded, and the linear adjustment unit is connected between the first end of the first capacitor and the first end of the power supply capacitor.

[0017] Optionally, after the switching power supply is started, the first capacitor is charged, and an auxiliary power supply voltage is generated on the first capacitor, and the auxiliary power supply voltage is used to provide a driving voltage for the second linear voltage regulator circuit.

[0018] Optionally, the second linear voltage stabilization circuit includes a second switching tube and a second diode, the second switching tube and the second diode are connected in series, the anode of the second diode is connected to the common connection end of the auxiliary power tube and the main power tube, and the cathode of the second diode is connected to the first end of the power supply capacitor.

[0019] Optionally, the second linear voltage stabilization circuit further includes a fourth switch tube, a first end of the fourth switch tube is connected to a control end of the second switch tube, the control end of the second switch tube receives the driving voltage, and a second end of the fourth switch tube is grounded;

[0020] When the PWM signal is valid, the fourth switch tube is turned off.

[0021] Optionally, the main power tube is a depletion-type transistor.

[0022] The present invention also provides a switching power supply, comprising a main power tube, an auxiliary power tube and an inductor connected to each other, characterized in that it also includes any one of the self-power supply circuits described above, and the self-power supply circuit generates a power supply voltage for powering a control chip of the switching power supply.

[0023] Compared with the prior art, the present invention has the following advantages: the present invention charges the system power supply capacitor through the inductive current of the power circuit, which greatly saves power consumption and improves system efficiency. Compared with the conventional auxiliary winding power supply scheme, the auxiliary winding and the rectifier diode are saved. At the same time, due to the provision of the first linear voltage stabilization circuit, the charging circuit is always in the standby state, the power supply capacitor capacity can be small, and only the high-frequency switch ripple needs to be filtered. When lightly loaded or dynamic, the charging circuit where the first linear voltage stabilization circuit is located can be automatically switched back, realizing the function of maintaining the power supply voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a self-powered circuit schematic diagram of a switching power supply in the prior art;

[0025] Figure 2 It is a working waveform diagram of the self-powered circuit in the prior art;

[0026] Figure 3 The self-powered circuit schematic diagram of the switching power supply of the present invention;

[0027] Figure 4 It is the working waveform diagram of the self-powered circuit of the present invention;

[0028] Figure 5The driving signal waveform diagram of the self-powered circuit of the present invention;

[0029] Figure 6 It is a working flow chart of the self-powered circuit of the present invention. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0031] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0032] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0033] like Figure 3 As shown, a schematic diagram of the self-powered circuit of the switching power supply of the present invention is illustrated. In this embodiment, the switching power supply is described by taking a flyback converter as an example. However, in the present invention, the switching power supply is not limited to a flyback converter, and may also be a buck converter, a boost converter, etc. The flyback converter of this embodiment rectifies the AC input voltage AC to obtain a DC input voltage Vin. The main power tube Q1 and the primary winding Np of the transformer T are connected in series, and the connection node is the switch node SW. The rectifier tube D0 and the secondary winding Ns of the transformer T are connected in series. By controlling the switch state of the main power tube Q1, the DC input voltage Vin is converted into the output voltage Vo through the transformer T. The self-powered circuit of the present invention comprises a power supply capacitor C0, a first linear voltage regulator circuit 01, a second linear voltage regulator circuit 02, an auxiliary power tube Q2, a first control circuit 03 and a driving circuit 04, the main power tube Q1 and the auxiliary power tube Q2 of the flyback converter are connected in series, the first linear voltage regulator circuit 01 is connected between the common connection end of the main power tube Q1 and the auxiliary power tube Q2 and the first end of the power supply capacitor C0, the second end of the power supply capacitor C0 is grounded, the second linear voltage regulator circuit 02 and the first linear voltage regulator circuit 01 are connected in parallel, the first control circuit 03 is used to control the on and off of the first linear voltage regulator circuit 01 and the auxiliary power tube Q2 according to the PWM signal, the driving circuit 04 receives the first control signal VC1 output by the first control circuit 03, and the output end is connected to the control end of the auxiliary power tube Q2, which is used to drive the on and off of the auxiliary power tube Q2. In the present invention, the main power tube Q1 is a depletion-type transistor, preferably a depletion-type gallium nitride transistor, which is a high-voltage tube.

[0034] When the switching power supply is just started, during the startup process, the first linear voltage regulator circuit 01 is turned on, and the DC input voltage Vin charges the power supply capacitor C0 through the primary winding Np of the transformer, the main power tube Q1 and the first linear voltage regulator circuit 01, and the excitation inductor stores energy. The power supply voltage VDD generated on the power supply capacitor C0 starts to rise from zero. When the power supply voltage VDD rises to the first threshold VDD1 (greater than or equal to the startup voltage of the chip), the first linear voltage regulator circuit 01 is turned off, and the power supply voltage VDD can make the control chip work normally, that is, the switching power supply can work normally. After the control chip works normally, a PWM signal is generated. By setting the first voltage regulator circuit 01 to provide a startup voltage for the control chip, and ensuring that the power supply voltage VDD is not lower than VDD1, it is ensured that the control chip can start normally. When the PWM signal is valid, the second linear voltage regulator circuit 02 is turned on, the first linear voltage regulator circuit 01 is turned off, the auxiliary power tube Q2 is turned off, and the DC input voltage Vin continues to charge the power supply capacitor C0 through the primary winding Np of the transformer, the main power tube Q1 and the second linear voltage regulator circuit 02, the excitation inductor continues to store energy, and the power supply voltage VDD generated on the power supply capacitor C0 continues to rise. In one way, when the power supply voltage VDD reaches the second threshold VDD2, the second linear voltage regulator circuit 02 is turned off and the auxiliary power tube Q2 is turned on. In another way, when the conduction time of the second linear voltage regulator circuit reaches the set time, the second linear voltage regulator circuit 02 is turned off and the auxiliary power tube Q2 is turned on. In either way, the purpose is to ensure that the power supply voltage VDD is sufficient to power the control chip of the switching power supply, and the power supply voltage VDD is not too high to affect the power supply efficiency. After the auxiliary power tube Q2 is turned on, the DC input voltage Vin completely stores energy in the excitation inductor through the main power tube Q1 and the auxiliary power tube Q2. When the PWM signal is invalid, the rectifier tube D0 on the secondary side is turned on, the energy stored in the excitation inductor is released to the output, and the main power tube Q1 and the auxiliary power tube Q2 are both turned off.

[0035] The first linear voltage regulator circuit 01 includes a diode D1, a first capacitor C1 and an LDO (low voltage linear regulator) 101. When the switching power supply is just started, the diode D1 and the LDO are turned on, the first capacitor C1 is charged, and an auxiliary power supply voltage VCC is generated on the first capacitor C1. The voltage VCC charges the capacitor C0 through the LDO to obtain a power supply voltage VDD. When the power supply voltage VDD reaches a first threshold value VDD1, the second linear voltage regulator circuit 02 is turned on. The second linear voltage stabilizing circuit 02 includes a diode D2, a switch tube Q3 and a switch tube Q4. The diode D2 and the switch tube Q3 are connected in series. The anode of the diode D1 is connected to the common connection end of the main power tube Q1 and the auxiliary power tube Q2. The cathode of the diode D1 is connected to the first end of the power supply capacitor C0. The first end of the switch tube Q4 is connected to the control end of the switch tube Q3. The second end of the switch tube Q4 is grounded. The control end of the switch tube Q3 and the first connection end of the switch tube Q4 also receive a driving voltage DRV1. The switch tube Q3 adopts an NMOS tube. Before the switch tube Q3 is turned on, the voltage VCC is approximately equal to the threshold voltage -Vgs_th of the switch tube Q1, and its value is greater than the voltage VDD (the source of the switch tube Q3). voltage), which can effectively drive the switch tube Q3 to turn on; when the PWM signal is valid, the first control circuit 03 controls the switch tube Q4 to turn off, the auxiliary power tube Q2 to turn off, and the drive voltage DRV1 generated according to the auxiliary power supply voltage VCC controls the switch tube Q3 to turn on. The DC input voltage Vin charges the power supply capacitor C0 through the diode D2 and the switch tube Q3. When the power supply voltage VDD reaches the second threshold VDD2, the switch tube Q4 of the first control circuit 03 is turned on, so that the control end of the switch tube Q3 is pulled down to the ground. The switch tube Q3 is turned off, that is, the second linear voltage regulator circuit 02 is turned off. At the same time, the first control circuit 03 also controls the auxiliary power tube Q2 to turn on through the drive circuit 04. The system power supply capacitor C0 is charged by the excitation inductor current of the power circuit of the flyback converter, which greatly saves power consumption and improves system efficiency compared with the high-voltage linear power supply scheme of the prior art. And compared with the conventional auxiliary winding power supply scheme, it saves auxiliary windings and rectifier diodes, and reduces power supply costs and volume. At the same time, since the first linear voltage regulator circuit 01 is always in standby mode, the capacity of the power supply capacitor C0 can be relatively small, and the power supply capacitor C0 only needs to filter the high-frequency switching ripple. When the switching power supply is lightly loaded or dynamic, since the main power tube Q1 is turned off for a long time, the power supply voltage VDD is sufficient to maintain the normal operation of the control chip. The first linear voltage regulator circuit 01 can be automatically turned on and can be automatically switched back as a charging circuit, thereby realizing the function of maintaining the power supply voltage VDD.

[0036] like Figure 4As shown, the working waveform diagram of the self-powered circuit of the present invention is illustrated. The waveform diagram is a waveform diagram when the switching power supply system works stably. Within a period of time after the main power tube Q1 is turned on, that is, at t1-t2, the gate-source voltage Vgs_Q3 of the switch tube Q3 is a high-level signal, the switch tube Q3 is turned on, and the DC input voltage Vin charges the power supply capacitor C0 and stores energy in the excitation inductor through the main power tube Q1 and the switch tube Q3. The charging current IQ3 and the inductor current I_Lm flowing through the switch tube Q3 gradually increase, the power supply voltage VDD on the charging capacitor C0 gradually increases, the voltage Vsw at the switch node SW decreases, and the voltage drop Vds_Q2 across the auxiliary power tube Q2 decreases. When the power supply voltage VDD reaches the second When the threshold VDD2 is reached (at time t2), the switch tube Q3 is turned off, and the gate-source voltage Vgs_Q3 of the switch tube Q3 becomes a low-level signal; at time t2-t3, the drive signal DRV of the auxiliary power tube Q2 is a high-level signal, driving the auxiliary power tube Q2 to turn on, and the DC input voltage Vin completely stores energy in the excitation inductor through the main power tube Q1 and the auxiliary power tube Q2. The power supply voltage VDD supplies power to the chip and gradually decreases. The auxiliary power tube Q2 is fully turned on, the voltage drop Vds is the smallest, the voltage Vds at both ends drops to the lowest, and the voltage Vsw at the switch node SW is the smallest; at time t2-t3, the main power tube Q1, the auxiliary power tube Q2 and the switch tube Q3 are all turned off, and the energy stored in the excitation inductor is released to the output end.

[0037] like Figure 5 As shown, the driving signal waveform diagram of the self-powered circuit of the present invention is illustrated. Figure 4Corresponding to the working waveform diagram, the PWM signal controls the on and off of the main power tube Q1. The PWM signal is valid when it is at a high level and invalid when it is at a low level. In the time period t1-t3, the PWM signal is valid at a high level, the main power tube Q1 is turned on, the excitation inductor stores energy, and i_Lm rises; in the time period t1-t2, within the time period (t1-t3) when the PWM signal is valid, the driving voltage DRV_VCC of the switch tube Q4 is invalid at a low level, the switch tube Q4 is turned off, the driving voltage Vgs_Q3 of the switch tube Q3 is valid at a high level, the switch tube Q3 is turned on, and the DC input voltage Vin charges the power supply capacitor V0 through the main power tube Q1 and the switch tube Q3, and the power supply voltage VDD rises; at t2, the power supply voltage VDD reaches the second threshold value VDD2, and in the time period t2-t3, DRV_VCC is high. The level is invalid, driving the switch tube Q4 to turn on, the driving voltage Vgs_Q3 of the switch tube Q3 is pulled down to the ground potential, the switch tube Q3 is turned off, the driving voltage DRV of the auxiliary power tube Q2 is valid at a high level, the auxiliary power tube Q2 is turned on, and the DC input voltage Vin completely stores energy in the excitation inductor through the main power tube Q1 and the auxiliary power tube Q2; during the t3-t4 period, the PWM low level is invalid, DRV_VCC remains at a high level, the switch tube Q4 is turned on, Vgs_Q3 continues to be pulled down, the switch tube Q3 continues to be turned off, DRV is invalid at a low level, the auxiliary power tube Q2 is turned off, and the excitation inductor releases energy to the load and output capacitor at the output end of the switching power supply. In the present invention, the time period t1-t2 is not limited, as long as the charging of the power supply capacitor C0 is completed within the PWM high-level effective time period so that the power supply voltage VDD can reach the second threshold value VDD2, that is, the present invention can also control the switch tube Q3 to be turned on and the auxiliary power tube Q2 to be turned off after the PWM signal switches from a low level to a high level for a period of time, and when the power supply capacitor C0 is charged and the power supply voltage VDD reaches the second threshold value VDD2, the switch tube Q3 is controlled to be turned off and the auxiliary power tube Q2 is turned on.

[0038] like Figure 6As shown, a working flow chart of the self-powered circuit of the present invention is illustrated, including steps S0, S1, ..., S6, S7, step S0, system power-on; step S1, the DC input voltage Vin is connected to form a charging circuit through the main power tube Q1, the diode D1, and the LDO to charge the power supply capacitor C0 until the power supply voltage VDD reaches the first threshold VDD1; step S2, the control chip is powered on and a PWM signal is generated; step S3, the PWM signal is valid, the switch tube Q3 is turned on, and the excitation current is connected to the charging circuit formed by the main power tube Q1, the diode D2 and the switch tube Q3 to charge the power supply capacitor C0; step S4, determine Whether the power supply voltage VDD is greater than the second threshold VDD2 (it can also be used to determine whether the conduction time of the second linear voltage regulator circuit reaches the set time). If so, enter step S5, otherwise return to step S3; S5, the switch tube Q3 is turned off, and the auxiliary power tube Q2 is turned on at the same time, and the excitation current passes through the power circuit where the main power tube Q1 and the auxiliary power tube Q2 are located to store energy in the excitation inductor; S6, the PWM signal is invalid, the main power tube Q1, the auxiliary power tube Q2 and the switch tube Q3 are all turned off, and the excitation inductor current transfers energy to the output; S7, a switching cycle ends, a new switching cycle begins, and returns to step S2 to repeat the above steps.

[0039] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0040] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A self-powered circuit of a switching power supply, the switching power supply comprising a main power tube, an auxiliary power tube and an inductor, the inductor is connected to a first end of the main power tube, the auxiliary power tube is connected between a second end of the main power tube and a ground end, characterized in that: include, A power supply capacitor, a first end of which is connected to the power supply end of the control chip of the switching power supply, a second end of which is grounded, and a first end of which generates a power supply voltage; A first linear voltage stabilizing circuit, connected between the first end of the power supply capacitor and the common connection end of the main power tube and the auxiliary power tube; A second linear voltage stabilizing circuit, connected in parallel with the first linear voltage stabilizing circuit; Among them, during the startup of the switching power supply, the first linear voltage regulator circuit is turned on and the power supply capacitor is charged; when the PWM signal generated by the control chip of the switching power supply is valid, the second linear voltage regulator circuit is turned on and the power supply capacitor is charged.

2. The self-powered circuit according to claim 1, characterized in that: When the PWM signal is valid, after the main power tube is turned on for a period of time, the second linear voltage stabilization circuit is turned on and the auxiliary power tube is turned off.

3. The self-powered circuit according to claim 1, characterized in that: When the PWM signal changes from invalid to valid, the second linear voltage stabilization circuit is turned on and the auxiliary power tube is turned off.

4. The self-powered circuit according to claim 1, characterized in that: When the supply voltage reaches a first threshold, the first linear voltage regulator circuit is turned off.

5. The self-powered circuit according to claim 1, characterized in that: When the supply voltage reaches a second threshold, the second linear voltage regulator circuit is turned off and the auxiliary power tube is turned on.

6. The self-powered circuit according to claim 1, characterized in that: When the conduction time of the second linear voltage regulator circuit reaches the set time, the second linear voltage regulator circuit is turned off, and the auxiliary power tube is turned on.

7. The self-powered circuit according to claim 1, characterized in that: The first linear voltage stabilization circuit includes a first capacitor, a first diode and a linear adjustment unit, the anode of the first diode is connected to the main power tube, the cathode of the first diode is connected to the first end of the first capacitor, the second end of the first capacitor is grounded, and the linear adjustment unit is connected between the first end of the first capacitor and the first end of the power supply capacitor.

8. The self-powered circuit according to claim 7, characterized in that: After the switching power supply is started, the first capacitor is charged, and an auxiliary power supply voltage is generated on the first capacitor. The auxiliary power supply voltage is used to provide a driving voltage for the second linear voltage stabilization circuit.

9. The self-powered circuit according to claim 8, characterized in that: The second linear voltage stabilization circuit includes a second switch tube and a second diode, the second switch tube and the second diode are connected in series, the anode of the second diode is connected to the common connection end of the auxiliary power tube and the main power tube, and the cathode of the second diode is connected to the first end of the power supply capacitor.

10. The self-powered circuit according to claim 9, characterized in that: The second linear voltage stabilizing circuit further includes a fourth switch tube, a first end of the fourth switch tube is connected to a control end of the second switch tube, the control end of the second switch tube receives the driving voltage, and a second end of the fourth switch tube is grounded; When the PWM signal is valid, the fourth switch tube is turned off.

11. The self-powered circuit according to claim 1, characterized in that: The main power tube is a depletion-type transistor.

12. A switching power supply, comprising a main power tube, an auxiliary power tube and an inductor connected to each other, characterized in that: It also includes the self-powered circuit described in any one of claims 1-11, wherein the self-powered circuit generates a power supply voltage for powering the control chip of the switching power supply.

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