TWI763527B - Flyback converter power supply and control method thereof - Google Patents

Abstract

A flyback converter power supply and a control method thereof are provided. The flyback converter power supply includes a transformer, a bipolar junction transistor, and a constant current and constant voltage control chip, the constant current and constant voltage control chip including: a constant current and constant voltage control module configured based on the primary winding characterizing the transformer The demagnetization induction signal of the demagnetization condition and the current sensing signal representing the current flowing through the primary winding of the transformer generate the switching control signal and the demagnetization sensing signal; the charging control module is configured to be based on the switching control signal and the demagnetization sensing signal. , generating first and second driving signals for driving the first and second field effect transistors to be turned on and off respectively. Under the condition that the constant current and constant voltage control chip works normally, when the first and second field effect transistors and the bipolar junction transistor are both in the off state, the current flowing through the starting resistance of the constant current and constant voltage control chip The chip power supply capacitor of the constant current and constant voltage control chip is charged through the charging path in the charging control module.

Description

Flyback converter power supply and control method thereof

The invention relates to the field of circuits, in particular to a flyback converter power supply and a control method thereof.

Flyback converter power supplies are widely used in the conversion between AC/DC (Alternate Current, AC/Direct Current, DC) and DC/DC (DC/DC), usually including power MOS field effect transistors, transformers, diodes , and capacitors, wherein: the Pulse Width Modulation (PWM) signal controls the on and off of the power MOS field effect transistor; when the power MOS field effect transistor is in the on state, the secondary winding of the transformer passes the induction The voltage across the primary winding of the transformer generates a first induced voltage, which makes the diode in a reverse biased state and cannot be turned on. At this time, the electrical energy stored in the capacitor provides voltage and current to the load; in the power MOS field effect When the transistor is in the off state, the secondary winding of the transformer generates a second induced voltage through the voltage across the primary winding of the inductive transformer, and the second induced voltage makes the diode in a forward biased state and conducts. The stored electrical energy is transferred to the capacitor and load.

A flyback converter power supply according to an embodiment of the present invention includes a transformer, a bipolar junction transistor, and a constant current and constant voltage control chip, wherein the collector of the bipolar junction transistor and the first terminal of the primary winding of the transformer connection, the base is connected with the base driving pin of the constant current and constant voltage control chip, and the emitter is connected with the emitter driving pin of the constant current and constant voltage control chip. The constant current and constant voltage control chip includes: a constant current and constant voltage control module, is configured to generate the switching control signal and the demagnetization sensing signal based on the demagnetization induction signal representing the demagnetization condition of the primary winding of the transformer and the current sensing signal representing the current flowing through the primary winding of the transformer; the charging control module is configured as Based on the switch control signal and the demagnetization sensing signal, generate a control chip for driving constant current and constant voltage respectively. The first and second driving signals for the turn-on and turn-off of the first and second field effect transistors, wherein, when the constant current and constant voltage control chip is in a normal working state, the turn-on of the bipolar junction transistor and the The turn-off depends on the turn-on and turn-off of the first and second field effect transistors, and when both the first and second field effect transistors and the bipolar junction transistor are in the off state, the The current of the starting resistor between the second terminal of the primary winding and the base driving pin charges the chip power supply capacitor connected to the chip power supply pin of the constant current and constant voltage control chip through the charging path in the charging control module.

A control method for a flyback converter power supply according to an embodiment of the present invention, wherein the flyback converter power supply includes a transformer, a bipolar junction transistor, and a constant current and constant voltage control chip, and a collection of bipolar junction transistors The electrode is connected to the first terminal of the primary winding of the transformer, the base electrode is connected to the base drive pin of the constant current and constant voltage control chip, and the emitter electrode is connected to the emitter drive pin of the constant current and constant voltage control chip. The control method includes: based on The demagnetization induction signal characterizing the demagnetization of the primary winding of the transformer and the current sensing signal characterizing the current flowing through the primary winding of the transformer generate the switch control signal and the demagnetization sensing signal; based on the switch control signal and the demagnetization sensing signal, generate respectively The first and second driving signals used to drive the turn-on and turn-off of the first and second field effect transistors in the constant current and constant voltage control chip, wherein the constant current and constant voltage control chip is in a normal working state , the turn-on and turn-off of the bipolar junction transistor depends on the turn-on and turn-off of the first and second field effect transistors, and when the first and second field effect transistors and the bipolar junction transistor are both off In the off state, the current flowing through the starting resistor connected between the second terminal of the primary winding of the transformer and the base drive pin is connected to the chip power supply pin of the constant current and constant voltage control chip through the charging path in the charging control module. Chip supply capacitor charging.

Compared with the traditional flyback converter power supply and the control method thereof, the flyback converter power supply and the control method thereof according to the embodiments of the present invention can reduce standby power and improve system efficiency.

100,100’: Flyback Converter Power Supply

102,102': constant current and constant voltage control chip

1022: Constant current and constant voltage control module

1024: Charging Control Module

AND2,AND3: AND gate

BASE: base drive pin

Co: filter capacitor

C2: Capacitor

comp1: comparator

Cvcc: chip power supply capacitor

CS: Current sensing pin

charge: charge control signal

D1: Diode

D2: Diode

D3: Diode

dem: Demagnetization sensing signal

FB: voltage feedback pin

GND: chip ground

I0: current source

I1: charging current

I2: Current

INV1, INV2, INV3: Inverters

M2, MN1, MN2, MN3, MN5, MP1, MP2, MP3, MP4: Field effect transistors

N _AUX : auxiliary winding

Np: primary winding

Ns: Secondary winding

ngate: the second drive signal

ngate2: the third drive signal

pgate: the first drive signal

pwm: switch control signal

pwm_d: switch control delay signal

Q1: Bipolar Junction Transistor

R1: Startup resistor

R2, R3: Voltage divider detection resistor

R5, R6, R7, R8: Resistors

R _S : Current sense resistor

SW: Emitter driver pin

T: Transformer

V _O : output voltage

VCC: chip power supply pin (voltage)

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the drawings, wherein:

Figure 1 shows a conventional transmitter stage-started, self-powered, primary-side controlled flyback converter power supply system circuit diagram.

FIG. 2 shows a system circuit diagram of a flyback converter power supply according to an embodiment of the present invention.

FIG. 3 shows an example circuit diagram of the charging control module shown in FIG. 2 .

FIG. 4 shows a timing diagram of various signals related to the charging control module when the constant current and constant voltage control chip shown in FIG. 2 is in a normal working state.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques have not been shown in order to avoid unnecessarily obscuring the present invention.

The flyback converter power supply with transmitter stage startup, self-power supply, and primary side control has the advantages of simple peripherals, low standby power consumption, and fast startup speed. FIG. 1 shows a system circuit diagram of a conventional launch-stage-started, self-powered, primary-side controlled flyback converter power supply 100 .

In the flyback converter power supply 100 shown in FIG. 1 , the constant current and constant voltage output is realized by using the constant current and constant voltage control chip 102 . Specifically, the working principle of the constant current and constant voltage control chip 102 is as follows: before the flyback converter power supply 100 is powered on, since the constant current and constant voltage control chip 102 is not powered, the field effect transistors MP1, MN1, M2 and the bipolar connection The surface transistors Q1 are all in the off state; after the flyback converter power supply 100 is powered on, the alternating current (AC) input voltage is rectified by the rectifier bridge and then charges the base driving pin BASE through the start-up resistor R1; since D2 prevents the current from passing through MP1 flow to VCC, therefore, as the base drive voltage at the base drive pin BASE gradually increases, the bipolar junction transistor Q1 changes from the off state to the on state, and the charging current I1 is generated; the charging current I1 flows from the emitter The driving pin SW flows through the diode D1 to the chip power supply pin VCC to charge the chip power supply capacitor Cvcc, and the voltage VCC on the chip power supply capacitor Cvcc continues to rise; When the voltage VCC on the chip power supply capacitor Cvcc is higher than the operating threshold of the constant current and constant voltage control chip 102 , the constant current and constant voltage control chip 102 starts to work.

When the constant current and constant voltage control chip 102 is in a normal working state, the constant current and constant voltage control module 1022 generates the driving signals pgate and ngate based on the demagnetization sensing signal at the voltage feedback pin FB and the current sensing signal at the current sensing pin CS , to drive the field effect transistors MP1 and MN1 on and off respectively. When the field effect transistor MP1 is in the on state and the field effect transistor MN1 is in the off state, the bipolar junction transistor Q1 is in the on state, and the transformer T stores energy; when the field effect transistor MP1 is in the off state and the field effect transistor is in the off state When MN1 is in the on state, the bipolar junction transistor Q1 is in the off state, and the energy stored in the transformer T is transmitted from the primary winding Np of the transformer T to the secondary winding Ns of the transformer T through coupling, while the auxiliary winding N of the transformer T is transmitted. _AUX generates a demagnetization induction signal through the demagnetization signal of the primary winding Np of the induction transformer T, and transmits the demagnetization induction signal to the inside of the constant current and constant voltage control chip 102 through the voltage feedback pin FB and the voltage divider resistor R2/R3 to realize the Closed loop control of flyback converter power supply 100 . The switching current of the primary side chip is transmitted to the secondary side through the transformer, and the output voltage Vo is generated through the rectifier diode D3 and the filter capacitor Co.

In the flyback converter power supply 100 shown in FIG. 1 , during the demagnetization of the primary winding Np of the transformer T, the field effect transistor MN1 is in an on state, and the bipolar junction transistor Q1 is in an off state. At this time, due to the existence of the start-up resistor R1, a loss current I2 to the ground will be generated. When the load of the flyback converter power supply 100 gradually decreases and enters a light load or no-load state, the time that the bipolar junction transistor Q1 is in the off state becomes longer, and the power loss generated by the starting resistor R1 becomes more and more obvious. , resulting in a significant increase in standby power consumption of the flyback converter power supply 100 and a decrease in system efficiency. If the resistance value of the start-up resistor R1 is increased, the start-up time after the flyback converter power supply 100 is powered on will become longer, making it difficult to meet the specification requirements.

FIG. 2 shows a system circuit diagram of a flyback converter power supply 100' according to an embodiment of the present invention. As shown in FIG. 2, similar to the flyback converter power supply 100, the flyback converter power supply 100' includes a transformer T, a bipolar junction transistor Q1, and a constant current and constant voltage control chip 102', wherein the bipolar junction The collector of the transistor Q1 is connected to the first terminal of the primary winding Np of the transformer T, the base is connected to the base driving pin BASE of the constant current and constant voltage control chip 102', and the emitter is connected is connected to the emitter drive pin SW of the constant current and constant voltage control chip 102'; the difference between the flyback converter power supply 100' and the flyback converter power supply 100 is that the constant current and constant voltage control chip 102' includes a constant current and constant voltage control In addition to the module 1022, a charging control module 1024 is also included.

As shown in FIG. 2 , in some embodiments, the constant current and constant voltage control module 1022 may be configured to be based on a demagnetization induction signal representing the demagnetization condition of the primary winding Np of the transformer T (ie, the constant current and constant voltage control chip 102 ′). the voltage signal at the voltage feedback pin FB) and the current sensing signal representing the current flowing through the primary winding Np of the transformer T (ie, the voltage signal at the current sensing pin CS of the constant current and constant voltage control chip 102'), generating a switch control signal pwm and a demagnetization sensing signal dem; the charging control module 1024 may be configured to generate a first circuit for driving the constant current and constant voltage control chip 102 ′ based on the switch control signal pwm and the demagnetization sensing signal dem and the first and second driving signals pgate and ngate for turning on and off the second field effect transistors MP1 and MN1.

As shown in FIG. 2 , in some embodiments, when the constant current and constant voltage control chip 102 ′ is in a normal working state, the turn-on and turn-off of the bipolar junction transistor Q1 depends on the first and second field effects The transistors MP1 and MN1 are turned on and off, and when the first and second field effect transistors MP1, MN1 and the bipolar junction transistor Q1 are all in the off state, flow through the primary winding Np connected to the transformer T The current I2 of the start-up resistor R1 between the second terminal of the constant current and constant voltage control chip 102' and the base driving pin BASE of the constant current and constant voltage control chip 102' supplies power to the chip of the constant current and constant voltage control chip 102' through the charging path in the charging control module 1024 The chip supply capacitor Cvcc connected to the pin VCC is charged. Here, since the current flowing through the startup resistor R1 is used to charge the chip power supply capacitor Cvcc when the bipolar junction transistor Q1 is off The standby power of the flyback converter power supply 100' is reduced and the system efficiency is improved.

As shown in FIG. 2 , in some embodiments, the charging control module 1024 may be further configured to generate a third power source for driving the constant current and constant voltage control chip 102 ′ based on the switch control signal pwm and the demagnetization sensing signal dem The third driving signal ngate2 for turning on and off the field effect transistor M2. During the startup process of the flyback converter power supply 100', before the voltage on the chip power supply capacitor Cvcc reaches the operating threshold of the constant current and constant voltage control chip 102', the first to the third The three field effect transistors MP1, MN1 and M2 are all in the off state; the AC input voltage is rectified by the rectifier bridge and then charges the base drive pin BASE through the start-up resistor R1; as the base drive voltage at the base drive pin BASE gradually increases rises, the bipolar junction transistor Q1 changes from the off state to the on state, and the charging current I1 flowing through the primary winding Np of the transformer T is generated; the charging current I1 passes through the emitter drive pin SW and is connected to the emitter drive pin SW The diode D1 between the chip power supply pin VCC charges the chip power supply capacitor Cvcc, and the voltage on the chip power supply capacitor Cvcc gradually increases; when the voltage on the chip power supply capacitor Cvcc is higher than the constant current and constant voltage control chip 102' work When the threshold value is reached, the constant current and constant voltage control chip 102' starts to work normally.

As shown in FIG. 2 , in some embodiments, when the constant current and constant voltage control chip 102 ′ is in a normal working state, when the first field effect transistor MP1 is in an on state and the second field effect transistor MN1 is in an off state In the off state, the bipolar junction transistor Q1 is in the on state; when the first field effect transistor MP1 changes from the on state to the off state and the second field effect transistor MN1 changes from the off state to the on state, the bipolar junction transistor Q1 is in the on state. The polarity junction transistor Q1 changes from the on state to the off state; after the bipolar junction transistor Q1 changes from the on state to the off state for a period of time, the second field effect transistor MN1 changes from the on state to the off state , that is, the first and second field effect transistors MP1 and MN1 and the bipolar junction transistor Q1 are all in an off state.

FIG. 3 shows an example circuit diagram of the charging control module 1024 shown in FIG. 2 . As shown in FIG. 3 , the charging control module 1024 may be further configured to: based on the switch control signal pwm, generate a first drive signal pgate for driving the first field effect transistor MP1 to be turned on and off; based on the switch control signal pwm and the demagnetization sensing signal dem, generating second and third driving signals ngate and ngate2 for driving the second and third field effect transistors MN1 and M2 to be turned on and off, respectively; and based on the switch control signal pwm and demagnetization The sensing signal dem generates a charging control signal charge for driving the charging path in the charging control module 1024 to be turned on and off. For example, the charging control module 1024 can be further configured to generate the second driving signal ngate by logically ANDing the inverted signal of the switch control signal pwm and the inverted signal of the charging control signal charge; and using the inverted signal of the charging control signal charge The phase signal is used as the third driving signal ngate2.

As shown in FIG. 3, in some embodiments, the resistor R5, the field effect transistor MP2, MP3, and resistor R6 form a charging path for charging the chip power supply capacitor Cvcc; when the field effect transistors MP2 and MP3 are in a conducting state, the base drive pin BASE is connected to the chip power supply pin VCC, and the start-up resistor R1 The current I2 charges the chip power supply capacitor Cvcc connected to the chip power supply pin VCC through the base drive pin BASE; the field effect transistors MN3 and MN2 and the resistors R7 and R8 are the control circuits that control the on and off of the field effect transistors MP2 and MP3 ; Field effect transistors MP4 and MN5, current source I0, capacitor C2, and comparator comp1 form a delay circuit, which generates a switch control delay signal pwm_d based on the switch control signal pwm; inverters INV1, INV2, INV3 and gates AND2, AND3 A timing control circuit is formed to generate first to third drive signals pgate, ngate, ngate2 and a charge control signal charge.

As shown in FIG. 3 , in some embodiments, the working process of the charging control module 1024 includes: generating the switch control delay signal pwm_d by sensing the falling edge of the switch control signal pwm; The inverted signal of the test signal dem is logically ANDed to generate the charge control signal charge; when the charge control signal charge is low, the field effect transistors MN2 and MN3 are in the off state, and the resistors R7 and R8 connect the field effect transistors MP3 and MN3 respectively. The gate of MP2 is short-circuited to the source, so that the voltage difference between the gate voltage and the source voltage of the field effect transistors MP3 and MP2 is less than their turn-on threshold, so that the field effect transistors MP2 and MP3 are in the off state, The charging path used to charge the chip power supply capacitor Cvcc is in the off state; during the period when the bipolar junction transistor Q1 is in the off state, after the switch control signal pwm changes from high level to low level after a fixed time delay, The charge control signal charge changes from a low level to a high level, while the second and third driving signals ngate and ngate2 change from a high level to a low level, and the second and third field effect transistors MN1 and M2 change from an on state to an off state state; when the charge control signal charge is at a high level, the field effect transistors MN2 and MN3 are in a conducting state. At the same time, due to the existence of the resistors R7 and R8, the gate electrodes of the field effect transistors MP2 and MP3 produce a voltage drop to the source electrodes. Appropriate resistance values of resistors R7 and R8 can make this voltage drop larger than the turn-on threshold of field effect transistors MP2 and MP3, so that field effect transistors MP3 and MP2 change from the off state to the on state; when the field effect transistors MP3 and MP2 When in the on state, the base drive pin BASE is connected to the chip power supply pin VCC, so that the The current I2 on the start-up resistor R1 flows through the base drive pin BASE to the chip power supply pin VCC to charge the chip power supply capacitor Cvcc.

FIG. 4 shows a timing diagram of various signals related to the charging control module 1024 when the constant current and constant voltage control chip 102' shown in FIG. 2 is in a normal working state. As shown in FIG. 4 , when the switch control signal pwm is at a high level, the first and second driving signals pgate and ngate are at a low level, the third driving signal ngate2 is at a high level, and the first and third field effect transistors MP1 and M2 In the on state, the second field effect transistor MN1 is in the off state, the base drive voltage at the base drive pin BASE is at a high level, the bipolar junction transistor Q1 is in the on state, and the primary winding of the transformer stores energy. When the switch control signal pwm is at a low level, the first and second driving signals pgate and ngate are at a high level, the first field effect transistor MP1 is in an off state, the second field effect transistor MN1 is in an on state, and the base driving pin The base drive signal at BASE is low, and the bipolar junction transistor Q1 is off. When the bipolar junction transistor Q1 is in the off state, after a fixed time delay after the switch control signal pwm changes from a high level to a low level, when the demagnetization sensing signal dem changes from a high level to a low level, the charging control signal The charge changes from a low level to a high level, and the charging path for charging the chip power supply capacitor Cvcc changes from an off state to an on state; when the charge control signal charge is at a high level, the first drive signal pgate is at a high level, the second and The third driving signals ngate and ngate2 are at low level, the first to third field effect transistors MP1, MN1 and M2 are all in the off state. At this time, the current I2 on the start-up resistor R1 can be controlled by charging through the base driving pin BASE. The charging path in the module 1024 flows to the chip power supply pin VCC to charge the chip power supply capacitor Cvcc. Here, since the current I2 flowing through the startup resistor R1 is used to charge the chip supply capacitor Cvcc, the flyback converter power supply 100' has lower standby power consumption and higher system efficiency than the flyback converter power supply 100.

In the flyback converter power supply 100' according to the embodiment of the present invention, after the bipolar junction transistor Q1 changes from the on state to the off state after a certain fixed time delay, the field effect transistor MN1 changes from the on state to the off state In the off state, the current I2 on the start-up resistor R1 charges the chip power supply capacitor Cvcc connected to the chip power supply pin VCC, so that the current I2 is stored in the chip power supply capacitor Cvcc to supply power to the constant current and constant voltage control chip 102', so that no additional power is generated. Power loss. Therefore, the constant current and constant voltage control chip can be accelerated by reducing the resistance value of the start-up resistor R1 102' start-up time without loss of power consumption and increase in standby power consumption.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the algorithms described in particular embodiments may be modified without departing from the basic spirit of the invention in system architecture. Accordingly, the present embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the present invention is defined by the appended claims rather than the foregoing description, and the meanings and equivalents falling within the claims All changes within the scope of the invention are thus included in the scope of the present invention.

100’: Flyback converter power supply

102': constant current and constant voltage control chip

1022: Constant current and constant voltage control module

BASE: base drive pin

Co: filter capacitor

Cvcc: chip power supply capacitor

CS: Current sensing pin

D1: Diode

D2: Diode

D3: Diode

dem: Demagnetization sensing signal

FB: voltage feedback pin

GND: chip ground

I1: charging current

I2: Current

M2, MN1MP1: Field Effect Transistor

N _AUX : auxiliary winding

Np: primary winding

Ns: Secondary winding

ngate: the second drive signal

ngate2: the third drive signal

pgate: the first drive signal

pwm: switch control signal

Q1: Bipolar Junction Transistor

R1: Startup resistor

R2, R3: Voltage divider detection resistor

R _S : Current sense resistor

SW: Emitter driver pin

T: Transformer

V _O : output voltage

VCC: chip power supply pin (voltage)

Claims (14)

A flyback converter power supply, comprising a transformer, a bipolar junction transistor, and a constant current and constant voltage control chip, wherein the collector of the bipolar junction transistor is connected to a first terminal of a primary winding of the transformer , the base is connected to the base drive pin of the constant current and constant voltage control chip, and the emitter is connected to the emitter drive pin of the constant current and constant voltage control chip, and the constant current and constant voltage control chip includes: a voltage control module configured to generate a switch control signal and a demagnetization sensing signal based on a demagnetization induction signal representing a demagnetization condition of the primary winding of the transformer and a current sensing signal representing a current flowing through the primary winding of the transformer ; a charging control module configured to generate the conduction and the second field effect transistor for driving the first and second field effect transistors in the constant current and constant voltage control chip, respectively, based on the switch control signal and the demagnetization sensing signal. The first and second driving signals are turned off, wherein when the constant current and constant voltage control chip is in a normal working state, the turning on and off of the bipolar junction transistor depends on the first and second driving signals. turn-on and turn-off of two field effect transistors, and when both the first and second field effect transistors and the bipolar junction transistor are in the off state, flow through the primary winding connected to the transformer The current of the start-up resistor between the second terminal of the constant current and constant voltage control chip and the base drive pin charges the chip power supply capacitor connected to the chip power supply pin of the constant current and constant voltage control chip through the charging path in the charging control module. The flyback converter power supply according to claim 1, wherein the charging control module is further configured to: based on the switch control signal, generate a turn-on and turn-off for driving the first field effect transistor the first drive signal; based on the switch control signal and the demagnetization sensing signal, the second drive signal for driving the second field effect transistor to be turned on and off is generated. The flyback converter power supply according to claim 1, wherein the charging control module is further configured to: generate a signal for driving the charging based on the switch control signal and the demagnetization sensing signal A charging control signal that controls the turn-on and turn-off of the charging path in the module. The flyback converter power supply of claim 3, wherein the charging control module is further configured to: generate a switch control delay signal by sensing a falling edge of the switch control signal; The delay signal and the inverted signal of the demagnetization sensing signal are logically ANDed to generate the charging control signal. The flyback converter power supply of claim 4, wherein the charging control module is further configured to: perform a logical AND of the inverted signal of the switch control signal and the inverted signal of the charging control signal , generating the second driving signal. The flyback converter power supply according to claim 1, wherein, under the condition that the constant current and constant voltage control chip is in a normal working state, when the first field effect transistor is in a conducting state and the second field effect transistor is in an on state When the effect transistor is in the off state, the bipolar junction transistor is in the on state. The flyback converter power supply of claim 1, wherein, when the constant current and constant voltage control chip is in the starting process, when both the first and second field effect transistors are in an off state and When the bipolar junction transistor is in an on state, the current flowing through the primary winding of the transformer passes through the emitter drive pin and the diode connected between the emitter drive pin and the chip power supply pin The body charges the chip supply capacitor. A control method for a flyback converter power supply, wherein the flyback converter power supply includes a transformer, a bipolar junction transistor, and a constant current and constant voltage control chip, the collector of the bipolar junction transistor It is connected with the first terminal of the primary winding of the transformer, the base is connected with the base driving pin of the constant current and constant voltage control chip, and the emitter is connected with the emitter driving pin of the constant current and constant voltage control chip. The control method includes: generating a switch control signal and a demagnetization sensing signal based on a demagnetization induction signal representing a demagnetization condition of a primary winding of the transformer and a current sensing signal representing a current flowing through the primary winding of the transformer; Based on the switch control signal and the demagnetization sensing signal, first and second drivers for driving the first and second field effect transistors in the constant current and constant voltage control chip to be turned on and off, respectively, are generated signal, wherein when the constant current and constant voltage control chip is in a normal working state, the turn-on and turn-off of the bipolar junction transistor depends on the turn-on and turn-off of the first and second field effect transistors. and when both the first and second field effect transistors and the bipolar junction transistor are in the off state, flow through the second terminal connected to the primary winding of the transformer and the base The current of the starting resistor between the driving pins charges the chip power supply capacitor connected to the chip power supply pin of the constant current and constant voltage control chip through the charging path in the charging control module. The control method according to claim 8, wherein, based on the switch control signal and the demagnetization sensing signal, the signals for driving the first and second field effect transistors to be turned on and off, respectively, are generated. The first and second drive signals include: based on the switch control signal, generating the first drive signal for driving the turn-on and turn-off of the first field effect transistor; based on the switch control signal and the The demagnetization sensing signal generates the second driving signal for driving the second field effect transistor to be turned on and off. The control method according to claim 8, further comprising: based on the switch control signal and the demagnetization sensing signal, generating a charge for driving on and off the charge path in the charge control module control signal. The control method according to claim 10, wherein, based on the switch control signal and the demagnetization sensing signal, generating the charging control signal for driving the charging path to be turned on and off comprises: by sensing The falling edge of the switch control signal generates a switch control delay signal; the charging control signal is generated by logically ANDing the switch control delay signal and the inverted signal of the demagnetization sensing signal. The control method of claim 11, wherein based on the switch control signal and the demagnetization sensing signal, all the parameters for driving the second field effect transistor to be turned on and off are generated. The second driving signal includes: generating the second driving signal by logically ANDing the inverted signal of the switch control signal and the inverted signal of the charging control signal. The control method according to claim 8, wherein when the constant current and constant voltage control chip is in a normal working state, when the first field effect transistor is in a conducting state and the second field effect transistor When in an off state, the bipolar junction transistor is in an on state. The control method of claim 8, wherein, when the constant current and constant voltage control chip is in the starting process, when both the first and second field effect transistors are in an off state and the dual When the polarity junction transistor is in the on state, the current flowing through the primary winding of the transformer is all connected by the emitter drive pin and the diode pair connected between the emitter drive pin and the chip power supply pin. The chip supply capacitor is charged.

Images