WO2021127957A1

WO2021127957A1 - Flyback converter constant-current control circuit

Info

Publication number: WO2021127957A1
Application number: PCT/CN2019/127739
Authority: WO
Inventors: 姜梅; 咸泉伟; 潘焕燕; 温勤琛
Original assignee: 深圳大学
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2021-07-01

Abstract

A flyback converter constant-current control circuit, comprising: a power tube driving module for generating a demagnetization end time according to a zero-crossing point of a gate end voltage of a flyback converter power tube in the current sampling period; a primary-side current peak and demagnetization time generation module for generating a primary-side current peak and a demagnetization start time according to an acquired primary-side sampling current of the current sampling period, and generating a demagnetization time according to the demagnetization start time and the demagnetization end time; and a control module for generating a primary-side current turn-off value according to the primary-side current peak and the demagnetization time of the current sampling period, and controlling, when a primary-side sampling current of the next sampling period is equal to the primary-side current turn-off value, the power tube driving circuit module to turn off the flyback converter power tube. A primary-side current turn-off value generated according to a primary-side current peak and a demagnetization time is compared with a primary-side sampling current of the next sampling period, and the turn-off time of a flyback converter power tube is controlled according to a comparison result, thereby realizing constant-current output control over a flyback converter.

Description

Constant current control circuit of flyback converter

Technical field

The application relates to the field of power supply control, and in particular to a flyback converter constant current control circuit.

Background technique

With the rapid development of electronic technology, there are more and more types and functions of electronic devices. The charging problem of portable electronic devices represented by mobile phones has become increasingly prominent. The output accuracy of the charger during charging affects the safety of charging. In another type of electronic equipment, taking LED lighting as an example, the current accuracy of the power supply directly affects the brightness of the lighting. At present, the flyback converter adopting the primary current feedback scheme is widely used in the field of power equipment because of the cost savings of optocouplers and the increase of system life. Since the accuracy of the constant current output of the flyback converter is directly affected by the current sampling accuracy, the demagnetization time sampling accuracy and the control scheme, and the current sampling error of the Miller platform caused by the power tube Miller capacitor, it causes the demagnetization in the prior art. The sampling accuracy of time and current is not high enough, which reduces the accuracy of the output current of the flyback converter.

Summary of the invention

Therefore, the technical problem to be solved by this application is to overcome the defects of inaccurate sampling of constant current control current and demagnetization time and low accuracy of output current in the prior art, thereby providing a flyback converter constant current control circuit.

To achieve the above objectives, this application provides the following technical solutions:

The present application provides a constant current control circuit for a flyback converter, including: a primary current peak value and demagnetization time generation module, a control module, and a power tube driving module. The power tube driving module is used for detecting current sampling Periodic flyback converter power tube gate terminal voltage zero crossing point, generate demagnetization end time, and send it to the primary side current peak value and demagnetization time generation module; primary side current peak value and demagnetization time generation module, used to obtain the current sampling The primary side sampling current of the periodic flyback converter generates the primary current peak value and the demagnetization start time, and generates the demagnetization time according to the demagnetization end time and the demagnetization start time, and sends the primary current peak value and demagnetization time of the current sampling period to Control module; control module, used to generate the primary current cut-off value according to the primary current peak value and demagnetization time of the current sampling period, and generate power when the primary sampling current of the next sampling cycle is equal to the primary current cut-off value The tube turn-off signal controls the power tube driving circuit module to turn off the flyback converter power tube.

In one embodiment, the flyback converter constant current control circuit further includes: a linear voltage stabilizing module and an oscillator module, wherein the linear voltage stabilizing module is used to obtain the auxiliary winding power supply input voltage and high voltage start of the flyback converter The input voltage provides a stable power supply for other modules in the constant current control circuit of the flyback converter; the oscillator module is used to provide a clock signal for the control module.

In an embodiment, the constant current control circuit of the flyback converter further includes: a reference parameter circuit module, an over-temperature protection circuit module, a startup circuit module, and an over-voltage protection circuit module, wherein the reference parameter circuit module is used for The other modules in the constant current control circuit of the excited converter provide electrical parameters; the over-temperature protection circuit module is used to generate the power switch when it is detected that the positive temperature coefficient voltage in the reference parameter circuit module exceeds the over-temperature voltage reference value. The signal is cut off and sent to the control module; the start circuit module is used to start the constant current control circuit function when the voltage start input voltage is detected to reach the start voltage reference value; the overvoltage protection circuit module is used to start the input when the voltage is detected When the voltage exceeds the reference value of the overvoltage voltage, disconnect the power supply of other modules except the starting circuit module and the overvoltage protection circuit module.

In an embodiment, the electrical parameters include: a starting voltage reference value, an overvoltage voltage reference value, an overtemperature voltage reference value, a turn-on voltage reference value, and a constant current value.

In one embodiment, the primary-side current peak value and demagnetization time generating module includes: a primary-side current peak value generating circuit, a demagnetization start time generating circuit, and a demagnetization time generating circuit. The sampling current of the primary side of the flyback converter in the sampling period generates the peak current of the primary side and sends it to the control module and the demagnetization start time generating circuit; the demagnetization start time generating circuit is used to generate the reference value of the conduction voltage and the current sampling period The peak current of the primary side of the flyback converter generates the demagnetization start time; the demagnetization time circuit is used to generate the demagnetization time according to the demagnetization end time and the demagnetization start time and send it to the control module.

In one embodiment, the control module includes: a primary side current turn-off value generating circuit and a drive signal generating circuit, wherein the primary side current turn-off value generating circuit is used to generate the primary side current peak value, demagnetization time, constant current value, The sampling period and the resistance value of the current cut-off resistance generate the primary current cut-off value; the drive signal generating circuit is used to compare the acquired primary sampling current of the next sampling cycle with the primary current cut-off value to generate the power tube shut-off value. Turn off the signal and send it to the power tube drive circuit module.

In an embodiment, the driving signal generating circuit is further used to generate a power tube turn-on signal according to the received clock signal, and send it to the power tube driving circuit module.

In one embodiment, when the flyback converter is in a steady state, the output current value of the secondary side of the flyback converter controlled by the constant current control circuit of the flyback converter is calculated by the following formula:

Among them, I _o is the output current of the secondary side of the flyback converter, k = N _p /N _s , N _p is the number of turns of the primary winding _{of the transformer, N s} is the number of turns of the secondary winding of the transformer, and R is the current shutdown resistance Value, R _CS is the resistance value of the sampling resistor, and I _c is the constant current value.

In an embodiment, the power tube driving module includes: a driving circuit field effect tube, the source of which is connected to the sampling resistor of the flyback converter, and is used to introduce the Miller platform current of the flyback converter power tube into the primary side In the current sampling circuit.

In one embodiment, a resistor is connected between the gate terminal of the field effect transistor of the driving circuit and the control module to filter out current spikes.

The technical solution of this application has the following advantages:

1. The flyback converter constant current control circuit provided by this application compares the primary side current cut-off value generated by the primary side current peak value and demagnetization time with the primary side sampling current of the next sampling period, and according to the comparison result Control the off time of the power tube of the flyback converter to realize the constant current output of the secondary side of the flyback converter.

2. The constant current control circuit of the flyback converter provided in this application takes into account the fact that the Miller platform brought by the Miller capacitor of the flyback converter power tube will sample the peak current of the primary side when the power tube is turned off. By collecting the current of the Miller platform, the sampling accuracy of the peak current of the primary side is improved; according to the peak current of the primary side, the demagnetization start time is obtained, and the power tube drive module collects the zero crossing point of the gate terminal voltage of the flyback converter power tube to obtain the demagnetization. The end time improves the sampling accuracy of the demagnetization time; the flyback converter controlled by the constant current control circuit of the flyback converter provided by this application can achieve a constant secondary side current by setting different turns ratios and sampling resistance values Output.

Description of the drawings

In order to more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the specific embodiments or the description of the prior art. Obviously, the appendix in the following description The drawings are some embodiments of the present application. For those of ordinary skill in the art, without creative work, other drawings can be obtained based on these drawings.

FIG. 1 is a circuit principle topology diagram of a specific example of a flyback converter provided by an embodiment of the application;

2 is a schematic diagram of a specific example of a flyback converter constant current control circuit provided by an embodiment of the application;

3 is a schematic diagram of a specific example of a flyback converter constant current control circuit provided by an embodiment of the application;

4 is a schematic diagram of a specific example of a flyback converter constant current control circuit provided by an embodiment of the application;

5 is a schematic diagram of a specific example of a flyback converter constant current control circuit provided by an embodiment of the application;

FIG. 6 is a schematic diagram of a specific example of a flyback converter constant current control circuit provided by an embodiment of the application.

Detailed ways

The technical solutions of the present application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of this application.

In the description of this application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the pointed device or element must have a specific orientation or a specific orientation. The structure and operation cannot therefore be understood as a limitation of this application. In addition, the terms "first", "second", and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

In the description of this application, it should be noted that the terms "installation", "connection", and "connection" should be understood in a broad sense, unless otherwise clearly specified and limited. For example, it can be a fixed connection or a detachable connection. Connected or integrally connected; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of the two components, it can be a wireless connection, or it can be a wired connection connection. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood under specific circumstances.

In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

Example

This embodiment provides a constant current control circuit for a flyback converter. In practical applications, the constant current control circuit can be integrated into a control chip for use in consumer electronic power supplies, portable electronic device charging, and replacement of other linear power supplies, etc. In the field, the embodiment of the application uses a flyback converter as a platform to verify the effectiveness of the constant current control function of the constant current control circuit. FIG. The circuit structure diagram of the side feedback flyback converter for constant current control. The main components include transformer, inductor, flyback converter power tube, rectifier diode, RCD circuit, auxiliary winding and constant current control circuit.

The primary side current of the flyback converter is proportional to the secondary side current, and the proportional relationship is shown in equation (1),

Among them, I _sp is the peak current of the secondary side, I _pp is the peak current of the primary side, N _p is the number of turns of the primary winding _{of the transformer, and N s} is the number of turns of the secondary winding of the transformer.

From the proportional relationship between the primary current and the secondary current shown in equation (1) and the periodic average current equation shown in equation (2), the relationship between the peak current of the secondary side and the peak current of the primary side and the demagnetization time can be obtained. As shown in formula (3).

Among them, I _o is the output current of the flyback converter, T _dm is the demagnetization time, and T _s is the sampling period.

From equation (3), it can be seen that the output current I _{o of the} flyback converter and the peak value of the primary current I _pp , the demagnetization time T _dm , the number of turns of the transformer primary coil N _p , the number of turns of the transformer secondary coil N _s, and the sampling period T _{s is} related, but the number of turns of the transformer primary winding N _p , the number of turns of the transformer secondary winding N _s and the sampling period T _s are given values, so the flyback can be controlled by controlling the primary current peak value I _pp and the demagnetization time T _dm The converter realizes constant current output.

This embodiment provides a flyback converter constant current control circuit, as shown in FIG. 2, including:

The power tube drive module is used to generate the demagnetization end time according to the detected zero crossing of the gate terminal voltage of the flyback converter power tube in the current sampling period, and send it to the primary current peak value and demagnetization time generation module.

The demagnetization time after the power tube of the flyback converter is turned off is obtained from the demagnetization start time and the demagnetization end time. In the embodiment of the present application, the demagnetization end time is detected by the power tube driving module. According to the working principle of the flyback converter, demagnetization ends when the voltage on the secondary side of the flyback converter decreases. At this time, the residual energy in the equivalent inductance of the transformer will be transferred to the equivalent inductance of the transformer and the flyback converter. The parasitic capacitance of the power tube forms an oscillation. This oscillating waveform can be detected at the drain terminal of the power tube of the flyback converter. The oscillating voltage waveform is transmitted to the gate terminal through the parasitic capacitance of the power tube of the flyback converter. When the power tube of the type converter is in the off state, the gate terminal is in a high impedance state, and the phase difference between the gate terminal voltage signal and the drain terminal voltage signal is 90 degrees. Therefore, when the power tube drive module detects the zero crossing of the gate terminal voltage, it is the end of demagnetization. time.

The primary side current peak value and demagnetization time generation module is used to generate the primary side current peak value and the demagnetization start time according to the acquired primary side sampling current of the flyback converter in the current sampling period, and generate according to the demagnetization end time and demagnetization start time Demagnetization time, the current peak value of the primary current of the current sampling period and the demagnetization time are sent to the control module.

The control module is used to generate the primary current cut-off value according to the primary current peak value and demagnetization time of the current sampling period. When the primary sampling current of the next sampling period is equal to the primary current cut-off value, the power tube is generated to turn off The signal control power tube drive circuit module turns off the flyback converter power tube.

After the flyback converter power tube is turned off, due to the demagnetization time of the equivalent inductance of the transformer, the primary sampling current does not drop rapidly, but after the flyback converter power tube is completely turned off, it suddenly drops to zero. At the same time, due to the influence of the Miller capacitance of the flyback converter, the primary current peak value is generated during the Miller plateau time. Therefore, the embodiment of the present application generates the primary side current peak value and the demagnetization time by sampling the Miller platform current The module obtains a more accurate primary current peak value of the current sampling period. The control module generates the primary current cut-off value of the next sampling period according to the primary current peak value of the current sampling period and the demagnetization time. When the current and the primary side current turn-off value are equal, the flyback converter power tube is turned off. In the embodiment of the present application, the constant current control of the flyback converter is realized by continuously adjusting the primary current cut-off value of each sampling period.

The flyback converter constant current control circuit provided by the embodiment of the application compares the primary side current cut-off value generated by the primary side current peak value and the demagnetization time with the primary side sampling current of the next sampling period, and according to the comparison result Control the off time of the power tube of the flyback converter to realize the constant current output of the secondary side of the flyback converter.

In a specific embodiment, the constant current control circuit of the flyback converter further includes:

The oscillator module is used to provide a clock signal for the control module. In the embodiment of the present application, when the primary side sampling current of the next cycle rises to the primary side current cut-off value, the control module generates a power tube turn-off signal to control the power tube drive circuit module to turn off the flyback converter power tube. After the power tube of the flyback converter is completely turned off, when the power tube of the flyback converter needs a driving signal to control the conduction, and the flyback converter power tube in the embodiment of the present application controls its conduction through the PWM modulation method. Therefore, the oscillator module provides a clock signal for the control module, and then the control module converts the clock signal into a power tube turn-on signal to control the power tube drive circuit module to turn on the flyback converter power tube.

The linear voltage stabilizing module is used to obtain the auxiliary winding power supply input voltage and high-voltage start input voltage of the flyback converter, and provide stable power for other modules in the constant current control circuit of the flyback converter. In the embodiment of the present application, when the flyback converter circuit is not started, no current flows in the auxiliary winding. At this time, the high-voltage start input voltage provides power. When the flyback converter circuit is operating normally, the converter The auxiliary winding power supply input voltage provides power. As shown in Figure 1, the Vs end of the flyback converter constant current control circuit is connected to one end of the voltage divider resistor, and the other end of the voltage divider resistor, Vsup, is connected to the auxiliary winding side. The output terminal VDD of the linear voltage regulator module outputs the supply voltage, which is used to provide stable power for other modules in the constant current control circuit of the flyback converter.

The reference parameter circuit module is used to provide electrical parameters for other modules in the constant current control circuit of the flyback converter. In the embodiments of the present application, the high-voltage startup input voltage or the auxiliary winding power supply input voltage is combined with parameter circuits such as resistor divider and operational amplifier to obtain state parameters such as voltage or current required for the operation of the constant current control circuit.

The over-temperature protection circuit module is used to generate a power tube shutdown signal and send it to the control module when it is detected that the positive temperature coefficient voltage in the reference parameter circuit module exceeds the over-temperature voltage reference value.

The starting circuit module is used to start the constant current control circuit function when it is detected that the voltage starting input voltage reaches the starting voltage reference value. As shown in Figure 1, the HV terminal of the constant current control circuit of the flyback converter is connected to the high-voltage starting input voltage, which is generated by the DC voltage output by the ac-dc rectifier diode circuit after being filtered by a filter.

The overvoltage protection circuit module is used to cut off the power supply of other modules except the starter circuit module and the overvoltage protection circuit module when it is detected that the high-voltage start input voltage exceeds the overvoltage voltage reference value.

In a specific embodiment, the electrical parameters include: a starting voltage reference value, an overvoltage voltage reference value, an overtemperature voltage reference value, a turn-on voltage reference value, and a constant current value. In the embodiments of the present application, multiple reference values of electrical parameters are compared with actual values, so as to obtain the voltage, current, etc., which are normally operated in the constant current control circuit. This is only an example, and is not limited to this.

In a specific embodiment, as shown in FIG. 3, the primary current peak value and demagnetization time generating module includes:

The primary side current peak value generating circuit is used to generate the primary side current peak value according to the acquired primary side sampling current of the flyback converter in the current sampling period, and send it to the control module and the demagnetization start time generating circuit.

As shown in Figure 1, the current sampling circuit is connected to one end of the sampling resistor in the embodiment of the application, and the sampling resistor voltage V _{cs is} collected as the related voltage of the primary sampling current of the current sampling period. Therefore, the peak value of the primary sampling current can be determined by the sampling The peak value of the resistance voltage is obtained, that is, I _pp =V _csp /R _cs , where I _pp is the peak value of the primary sampling circuit, R _cs is the resistance value of the resistor, and V _csp is the peak value of the sampling resistor voltage. In order to obtain the peak value of the sampling resistor voltage V _csp , The embodiment of the application builds the circuit as shown in FIG. 3. In Figure 3, VDD is the power supply voltage output by the linear regulator module, V _cs is the sampling resistor voltage, V _ref is the reference value of the turn-on voltage, t _{dm_on} is the demagnetization start time, M1 is the P-type MOS field effect tube, and A1 is the calculation Amplifier, C1 is the charging capacitor, R1 is the filter resistance.

As shown in Figure 3(a), after the flyback converter power tube is turned off, because the power tube has a turn-off delay time, and because the P-type MOS tube can only pull up the drain voltage from VDD, M1 In the on state, the embodiment of the present application charges the charging capacitor C1 _{with the sampling resistor voltage V cs through the operational amplifier A1 and the M1 field effect transistor.} Due to the unidirectional conductivity of the MOS, the capacitor can only be charged and not discharged during the charging period, so after the power tube is turned off, the current peak value V _csp during the charging capacitor charged by the sampling resistor voltage can be collected.

The demagnetization start time generating circuit is used to generate the demagnetization start time according to the reference value of the conduction voltage and the peak value of the primary current of the flyback converter in the current sampling period. As shown in Figure 3(b), when the power tube of the flyback converter is completely turned off, the sampling resistor voltage V _cs suddenly drops due to the sudden drop of the primary current peak value to zero. This time is the demagnetization start time. A1 pulls the gate terminal of M1 to a high level to turn off the M1 tube. By comparing the on-voltage reference value V _ref with the output voltage of A1, the demagnetization start time information can be obtained.

The demagnetization time circuit is used to generate the demagnetization time according to the demagnetization end time and the demagnetization start time and send it to the control module.

In a specific embodiment, the control module includes:

The primary current cut-off value generating circuit is used to generate the primary current cut-off value according to the primary current peak value, demagnetization time, constant current value, sampling period, and current cut-off resistance value.

The embodiment of this application, as shown in Figure 4(b), when the demagnetization has not started, that is, when the primary current peak value and the demagnetization time generating module does not generate the demagnetization start time, the power tube in Figure 4(a) has no drive signal , The constant current source charges the capacitor C; when the demagnetization starts, the capacitor C begins to discharge. In the steady state of the flyback converter, the charging current of the capacitor C is equal to the discharge current, so it can be at the current cut-off resistance value R When the demagnetization time is detected, the charging voltage V _C can be calculated by equation (4):

Among them, V _C is the demagnetization time charging voltage, R is the resistance value of the current shut-off resistance, T _s is the sampling period, and T _dm is the demagnetization time.

The peak value of the sampling resistor voltage V _{csp is} compared with the demagnetization time charging voltage V _C through the error amplifier. When V _{csp is} greater than V _C , the cut-off value is lowered, and when V _{csp is} lower than V _C , the cut-off value is increased to generate the sampling resistor voltage to turn off. The value V _csgd is the primary current cut-off value.

The driving signal generation circuit is used to compare the acquired primary side sampling current of the next sampling period with the primary side current turn-off value, generate a power tube turn-off signal and send it to the power tube drive circuit module.

As shown in Figure 5(a), the embodiment of the present application uses the drive signal generating circuit to detect when the primary current of the next sampling period rises to reach the primary current cut-off value, that is, the sampling resistor voltage V _cs reaches the sampling resistor voltage The turn-off value V _{csgd turns} off the power tube of the flyback converter. After a certain period of time, the power tube of the flyback converter is completely turned off. At this time, the peak value of the sampling resistor voltage in the next sampling period can reach the peak value of the sampling resistor voltage V _csp . When the voltage peak value cannot reach the sampling resistor voltage peak value V _csp _{, the sampling resistor voltage cut-off value V csgd is} continuously adjusted through the primary current peak value and demagnetization time generation module and control module to control the sampling resistor voltage peak value in the next sampling period to achieve sampling The peak value of the resistance voltage V _csp .

In a specific embodiment, the driving signal generating circuit is further used to generate a power tube turn-on signal according to the received clock signal, and send it to the power tube driving circuit module.

In a specific embodiment, when the flyback converter is in a steady state, the output current value of the secondary side of the flyback converter controlled by the constant current control circuit of the flyback converter is calculated by the following formula:

In the embodiment of the present application, when the flyback converter circuit reaches a steady state, that is, when the secondary side output current is a preset constant value, at this time V _csp =V _c , as shown in Figure 5(b), according to the formula ( 3) and formula (4) can obtain formula (5). It can be seen from equation (5) that when the flyback converter is in a steady state, the output current value of the secondary side of the flyback converter controlled by the constant current control circuit of the flyback converter is only proportional to the transformer turns ratio k and current The turn-off resistance value R, the constant current value I _c, and the sampling resistance R _{cs are} related and are all given design values. Therefore, the flyback converter controlled by the flyback converter constant current control circuit provided in this embodiment is The constant output of the secondary side current can be achieved by specifying different turns ratios and sampling resistance values.

In a specific embodiment, the power tube drive module includes: a drive circuit FET, the source of which is connected to the sampling resistor of the flyback converter, and is used to introduce the Miller platform current of the flyback converter power tube into the original Edge current sampling circuit. And a resistor is connected between the gate terminal of the field effect tube of the driving circuit and the control module to filter out current spikes.

As shown in FIG. 6(a) and FIG. 6(b), in the embodiment of the present application, the source terminal of the field effect transistor of the driving circuit is not grounded, but is connected to the sampling resistor. In this way, when the flyback converter power tube is turned off, the current overcharge caused by the Miller platform caused by the Miller capacitor can be sampled, and the accurate primary current peak value can be sampled. As shown in Figure 6(d), this connection will introduce a current spike in the primary current when the drive circuit FET is turned off, so a resistor is added to the gate of the drive tube to filter out the spike, such as As shown in Figure 6(c). Compared with Figure 6(d) and Figure 6(e), after the filter resistor is connected, the current spike no longer affects the sampling.

In order to verify the correctness of the flyback converter constant current control circuit provided by the embodiment of the application, the embodiment of the application completes the design and simulation through Nuvoton's 350nm BCD process ntc1132 (this is only used as an example, not limited to this) , It is measured that when the input voltage of the chip in the flyback system varies from 85Vac to 220Vac, and the secondary side load changes from 6W to 23W, the deviation of the secondary side output current value is within ±1.46%.

The flyback converter constant current control circuit provided by the embodiment of the application controls the flyback converter according to the primary current cut-off value generated by the primary current peak value and the demagnetization time, and the primary sampling current of the next sampling period The turn-off time of the power tube realizes the constant current output of the secondary side of the flyback converter; considers the Miller platform brought by the miller capacitor of the power tube of the flyback converter to the primary side current when the power tube is turned off. The impact of peak sampling improves the sampling accuracy of the peak current of the primary side by collecting the current of the Miller platform; according to the peak current of the primary side, the demagnetization start time is obtained, and the power tube drive module collects the gate terminal voltage of the power tube of the flyback converter. Zero crossing point, get the demagnetization end time, the primary current peak value and demagnetization time generation module collects the on-voltage of the P-type MOS tube, and obtains the demagnetization start time, which improves the sampling accuracy of the demagnetization time; the flyback converter provided by this application has a constant current The flyback converter controlled by the control circuit can achieve a constant output of the secondary side current by specifying different turns ratios and sampling resistance values.

Obviously, the above-mentioned embodiments are merely examples for clear description, and are not intended to limit the implementation manners. For those of ordinary skill in the art, other changes or modifications in different forms can be made on the basis of the above description. It is unnecessary and impossible to list all the implementation methods here. The obvious changes or changes derived from this are still within the scope of protection created by this application.

Claims

A constant current control circuit for a flyback converter, which is characterized by comprising: a primary side current peak value and demagnetization time generating module, a control module, and a power tube driving module, wherein:

The power tube driving module is used to generate the demagnetization end time according to the detected zero crossing point of the gate terminal voltage of the flyback converter power tube of the current sampling period, and send it to the primary current peak value and demagnetization time generation module;

The primary side current peak value and demagnetization time generating module is used to generate the primary side current peak value and the demagnetization start time according to the acquired primary side sampling current of the flyback converter in the current sampling period, and according to the demagnetization end time and the The demagnetization start time generates the demagnetization time, and the primary current peak value and the demagnetization time of the current sampling period are sent to the control module;

The control module is used to generate the primary current cut-off value according to the primary current peak value and demagnetization time of the current sampling period, and generate the primary current cut-off value when the primary sampling current of the next sampling cycle is equal to the primary current cut-off value The power tube turn-off signal controls the power tube driving circuit module to turn off the flyback converter power tube.
The flyback converter constant current control circuit according to claim 1, further comprising: a linear voltage stabilizing module and an oscillator module, wherein,

Linear voltage stabilizing module, used to obtain the auxiliary winding power supply input voltage and high-voltage start input voltage of the flyback converter, and provide stable power for other modules in the constant current control circuit of the flyback converter;

The oscillator module is used to provide a clock signal for the control module.
The flyback converter constant current control circuit according to claim 2, further comprising: a reference parameter circuit module, an over-temperature protection circuit module, a starting circuit module, and an over-voltage protection circuit module, wherein:

The reference parameter circuit module is used to provide electrical parameters for other modules in the constant current control circuit of the flyback converter;

The over-temperature protection circuit module is used to generate a power tube shutdown signal and send it to the control module when it is detected that the positive temperature coefficient voltage in the reference parameter circuit module exceeds the over-temperature voltage reference value;

The starting circuit module is used to start the function of the constant current control circuit when it is detected that the voltage starting input voltage reaches the starting voltage reference value;

The overvoltage protection circuit module is used to cut off the power supply of other modules except the starter circuit module and the overvoltage protection circuit module when it is detected that the voltage start input voltage exceeds the overvoltage voltage reference value.
The flyback converter constant current control circuit according to claim 3, wherein the electrical parameters include: a starting voltage reference value, an overvoltage voltage reference value, an overtemperature voltage reference value, and a turn-on voltage reference value And constant current value.
The flyback converter constant current control circuit according to claim 4, wherein the primary current peak value and demagnetization time generating module includes: a primary current peak value generating circuit, a demagnetization start time generating circuit, and a demagnetizing time generating module Circuit, where

The primary side current peak value generating circuit is configured to generate the primary side current peak value according to the acquired primary side sampling current of the flyback converter in the current sampling period, and send the primary side current peak value to the control module and the demagnetization start time generating circuit;

A demagnetization start time generating circuit for generating the demagnetization start time according to the reference value of the on-voltage and the peak current of the primary side of the flyback converter in the current sampling period;

The demagnetization time circuit is used to generate the demagnetization time according to the demagnetization end time and the demagnetization start time and send it to the control module.
The flyback converter constant current control circuit according to claim 5, wherein the control module comprises: a primary current cut-off value generating circuit and a driving signal generating circuit, wherein:

A primary side current cut-off value generating circuit, configured to generate a primary side current cut-off value according to the primary current peak value, the demagnetization time, the constant current value, the sampling period, and the current cut-off resistance value;

The driving signal generating circuit is used to compare the acquired primary side sampling current of the next sampling period with the primary side current turn-off value, generate a power tube turn-off signal and send it to the power tube driving circuit module.
The flyback converter constant current control circuit according to claim 6, wherein the drive signal generating circuit is also used to generate a power tube turn-on signal according to the received clock signal, and send it to the power tube Drive circuit module.
The flyback converter constant current control circuit according to claim 6, wherein when the flyback converter is in a steady state, the flyback converter controlled by the flyback converter constant current control circuit The output current value of the secondary side of the type converter is calculated by the following formula:

Among them, I o is the output current of the secondary side of the flyback converter, k = N p /N s , N p is the number of turns of the primary winding of the transformer, N s is the number of turns of the secondary winding of the transformer, and R is the current shutdown resistance Value, R CS is the resistance value of the sampling resistor, and I c is the constant current value.
The flyback converter constant current control circuit according to claim 8, wherein the power tube driving module comprises: a drive circuit field effect tube, the source of which is connected to the sampling resistor of the flyback converter, To introduce the Miller platform current of the flyback converter power tube into the primary current sampling circuit.
The constant current control circuit of the flyback converter according to claim 9, wherein a resistor is connected between the gate terminal of the field effect transistor of the driving circuit and the control module for filtering current spikes.