CN118868564A - Switching power supply and its control circuit - Google Patents

Abstract

A switching power supply and a control circuit thereof, wherein the switching power supply comprises a chip startup resistor and a chip power supply capacitor, and the control circuit comprises a charging control switch circuit and is configured to: during the startup process of the switching power supply, control the charging control switch circuit to be in an on state, so that the AC input voltage of the switching power supply charges the chip power supply capacitor via the chip startup resistor and the charging control switch circuit.

Description

Switching power supply and its control circuit

Technical Field

The present invention relates to the field of circuits, and more particularly to a switching power supply and a control circuit thereof.

Background Art

A switching power supply, also known as an exchange power supply or a switching converter, is a type of power supply. The function of a switching power supply is to convert a DC or AC voltage into the voltage or current required by the user through different forms of architecture (for example, flyback architecture, forward architecture, buck architecture, or boost architecture, etc.).

Summary of the invention

According to an embodiment of the present invention, a control circuit is used in a switching power supply, wherein the switching power supply includes a chip startup resistor and a chip power supply capacitor, and the control chip includes a charging control switch circuit and is configured as follows: during the startup process of the switching power supply, the charging control switch circuit is controlled to be in an on state, so that the AC input voltage of the switching power supply charges the chip power supply capacitor via the chip startup resistor and the charging control switch circuit.

A switching power supply according to an embodiment of the present invention includes the above control circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 shows a schematic diagram of the structure of a conventional flyback switching power supply.

FIG. 2 shows a schematic structural diagram of a flyback switching power supply according to an embodiment of the present invention.

FIG. 3 shows a timing diagram of the operation of a plurality of charging control related signals shown in FIG. 2 .

FIG. 4 shows an example implementation circuit diagram of the charging control module shown in FIG. 2 .

DETAILED DESCRIPTION

The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, parts and algorithms without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention. In addition, it should be noted that the term "A is connected to B" used here can mean "A is directly connected to B" and can also mean "A is indirectly connected to B via one or more other elements".

Fig. 1 shows a schematic diagram of the structure of a conventional flyback switching power supply. As shown in Fig. 1, in the flyback switching power supply 100, the system output voltage Vo of the flyback switching power supply 100 is sampled by using the auxiliary winding Naux of the transformer T to generate an output voltage feedback signal FB representing the system output voltage Vo, the primary current Ip flowing through the primary winding Np of the transformer T is detected by using the current sensing resistor Rs to generate a primary current detection signal CS representing the primary current Ip, and constant voltage/constant current control of the system output voltage/current is achieved through logic control based on the output voltage feedback signal FB and the primary current detection signal CS.

As shown in FIG1 , in the flyback switching power supply 100: the power tube Q1 is connected between the primary winding Np of the transformer T1 and the reference ground, the driving tube MN1 is connected between the base of the power tube Q1 and the reference ground, and the driving tube MP1 is connected between the chip power supply capacitor Cvcc and the base of the power tube Q1; before the system is turned on, the driving tubes MP1 and MN1, the switch tube M2, and the power tube Q1 are all in the off state; after the system is turned on, the AC input voltage AC is rectified by the rectifier bridge and charges the base of the power tube Q1 through the chip startup resistor R1; as the base voltage of the power tube Q1 increases, the power tube Q1 changes from the off state to the on state, and the AC input voltage AC is turned on at the power The charging current I1 generated on the power tube Q1 flows from the switching pin SW of the control chip 102 via the diode D1 to the power pin VCC of the control chip 102 to charge the chip power supply capacitor Cvcc; when the chip power supply voltage VCC on the chip power supply capacitor Cvcc is higher than the undervoltage lockout (UVLO) threshold of the control chip 102, the control chip 102 starts to work; after the control chip 102 works normally, the constant voltage/constant current control module generates a power tube control signal pwm (not shown in the figure) for controlling the conduction and shutdown of the power tube Q1 based on the output voltage feedback signal FB and the primary current detection signal CS, and generates a control signal pwm for controlling the driving tube MN1 based on the power tube control signal pwm. The first driving tube control signal ngate for turning on and off and the second driving tube control signal pgate for controlling the turning on and off of the driving tube MP1; when the driving tube MP1 is in the on state and the driving tube MN1 is in the off state, the power tube Q1 is in the on state, and the primary winding Np of the transformer T stores energy; when the driving tube MP1 is in the off state and the driving tube MN1 is in the on state, the power tube Q1 is in the off state, and the energy stored in the primary winding Np of the transformer T is transferred to the secondary winding Ns of the transformer T, and the auxiliary winding Naux of the transformer T generates a voltage proportional to the system output voltage Vo by coupling the demagnetization signal of the secondary winding Ns; The voltage-dividing resistors R9 and R10 divide the voltage on the auxiliary winding Naux of the transformer T to generate an output voltage feedback signal FB; when the control chip 102 is working normally and the power tube Q1 is in the off state, if the chip power supply voltage VCC on the chip power supply capacitor Cvcc is lower than the predetermined power supply threshold (i.e., the self-power supply of the control chip 102 is insufficient), the base voltage of the power tube Q1 is pulled up through the chip startup resistor R1, so that the power tube Q1 changes from the off state to the on state, and the charging current I1 flows from the switching pin SW of the control chip 102 via the diode D1 to the power pin VCC of the control chip 102 to charge the chip power supply capacitor Cvcc.

The flyback switching power supply 100 shown in FIG1 has the following disadvantages, that is, when the AC input voltage AC is high or ultra-high voltage, due to the low withstand voltage between the collector and the emitter of the power tube Q1, the power tube Q1 is prone to breakdown and damage when the chip power supply capacitor Cvcc is charged when the system is normally started or the self-power supply of the control chip 102 is insufficient. However, if the chip power supply capacitor Cvcc is charged simply through the chip startup resistor R1 without the power tube Q1, it is easy to cause insufficient self-power supply of the control chip 102 when the AC input voltage AC is low.

In view of the above situation, a control chip used in a switching power supply according to an embodiment of the present invention is proposed, which can prevent the power tube in the switching power supply from being broken down and damaged when the system is started normally or the self-power supply of the control chip is insufficient, and can also prevent the self-power supply of the control chip from being insufficient when the AC input voltage is low voltage.

FIG2 shows a schematic diagram of the structure of a flyback switching power supply according to an embodiment of the present invention. As shown in FIG1 and FIG2, the flyback switching power supply 200 is different from the flyback switching power supply 100 in that the control chip 102 is replaced by the control chip 202, and the control chip 202 is configured to: during the startup process of the flyback switching power supply 200, control the charging control switch circuit to be in a conducting state, so that the AC input voltage AC charges the chip power supply capacitor Cvcc via the chip startup resistor R1 and the charging control switch circuit (that is, the charging current I2 generated by the AC input voltage AC on the chip startup resistor R1 charges the chip power supply capacitor Cvcc via the charging control switch circuit).

As shown in FIG2 , in some embodiments, the control chip 202 is further configured to: during the normal operation of the flyback switching power supply 200, when the power tube Q1 is in the off state and the chip power supply voltage VCC on the chip power supply capacitor Cvcc is less than a predetermined power supply threshold, if the AC input voltage AC of the flyback switching power supply 200 is greater than or equal to the predetermined input threshold, control the charging control switch circuit to be in the on state, so that the AC input voltage AC charges the chip power supply capacitor Cvcc via the chip startup resistor R1 and the charging control switch circuit (that is, the charging current I2 charges the chip power supply capacitor Cvcc); otherwise, control the driving tube MN1 connected between the base of the power tube Q1 and the reference ground to change from the on state to the off state, so that the AC input voltage AC charges the base of the power tube Q1 via the chip startup resistor R1, and after the power tube Q1 changes from the off state to the on state as its base voltage increases, the AC input voltage AC charges the chip power supply capacitor Cvcc via the power tube Q1 (that is, the charging current I1 charges the chip power supply capacitor Cvcc).

As shown in FIG. 2 , in some embodiments, the control chip 202 includes a power supply voltage detection module 2022, a line voltage detection module 2024, a constant voltage/constant current control module 2026, and a charging control module 2028, wherein: the power supply voltage detection module 2022 is configured to generate a power supply status indication signal VCC_low indicating whether the chip power supply voltage VCC on the chip power supply capacitor Cvcc is less than a predetermined power supply threshold based on the chip power supply voltage VCC on the chip power supply capacitor Cvcc; the line voltage detection module 2024 is configured to generate an input voltage indication signal H indicating whether the AC input voltage AC is greater than or equal to a predetermined input threshold based on the output voltage feedback signal FB. ighline; the constant voltage/constant current control module 2026 is configured to generate a demagnetization state indication signal dem based on the output voltage feedback signal FB, which indicates whether the secondary winding Ns of the transformer T is in a demagnetization state, and to generate a power tube control signal pwm for controlling the on and off of the power tube Q1 based on the output voltage feedback signal FB and the primary current detection signal CS; the charging control module 2028 is configured to control the on and off of the charging control switch circuit, the driving tubes MN1 and MP1, and the switch tube M2 based on the power supply state indication signal VCC_low, the input voltage indication signal Highline, the power tube control signal pwm, and the demagnetization state indication signal dem.

As shown in FIG. 2 , in some embodiments, the charging control module 2028 is further configured to: generate a first driving tube control signal ngate for controlling the on and off of the driving tube MN1 based on the power tube control signal pwm, the demagnetization state indication signal dem, and the power supply state indication signal VCC_low (for example, generate a demagnetization end indication signal dem_b indicating whether a predetermined time has passed since the demagnetization end moment of the secondary winding Ns of the transformer T based on the demagnetization state indication signal dem, and generate a first power tube control signal ngate for controlling the on and off of the driving tube MN1 based on the power tube control signal pwm, the demagnetization state indication signal dem, and the power supply state indication signal VCC_low and generating a charging switch control signal charge for controlling the on and off of the charging control switch circuit based on the power tube control signal pwm, the demagnetization state indication signal dem, the power supply state indication signal VCC_low, and the input voltage indication signal Highline (for example, generating a demagnetization end indication signal dem_b based on the demagnetization state indication signal dem, and generating a charging switch control signal charge based on the power tube control signal pwm, the demagnetization end indication signal dem_b, the power supply state indication signal VCC_low, and the input voltage indication signal Highline).

As shown in Figure 2, in some embodiments, the charging control module 2028 is further configured to: generate a switch tube control signal ngate2 for controlling the conduction and shutdown of the switch tube M2 based on the power tube control signal pwm, the demagnetization state indication signal dem, the power supply state indication signal VCC_low, and the input voltage indication signal Highline (for example, generate a demagnetization end indication signal dem_b based on the demagnetization state indication signal dem, and generate a charging switch control signal charge based on the power tube control signal pwm, the demagnetization end indication signal dem_b, the power supply state indication signal VCC_low, and the input voltage indication signal Highline).

As shown in FIG2 , in some embodiments, the control circuit 202 is further configured to generate a second drive tube control signal pgate for controlling the on and off of the drive tube MP1 connected between the base of the power tube Q1 and the chip power supply capacitor Cvcc based on the power tube control signal pwm.

As shown in FIG. 2 , in the flyback switching power supply 200: before the system is turned on, the driving tubes MP1 and MN1, the switch tube M2, and the power tube Q1 are all in the off state; after the system is turned on, the AC input voltage AC is rectified by the rectifier bridge and then charges the chip power supply capacitor Cvcc via the chip startup resistor R1 and the charging control switch circuit (that is, the charging current I2 charges the chip power supply capacitor Cvcc via the charging control switch circuit); when the chip power supply voltage VCC on the chip power supply capacitor Cvcc is higher than the UVLO threshold of the control chip 202, the control chip 202 starts to work; during the normal working process of the system In the embodiment, when the power tube control signal pwm is at a logic high level, the first and second drive tube control signals ngate and ngate are at a logic low level, the drive tube MP1 is in a conducting state, the drive tube MN1 is in a shut-off state, the power tube Q1 is in a conducting state, the switch tube control signal ngate2 is at a logic high level, and the switch tube M2 is in a conducting state; when the power tube control signal pwm is at a logic low level, the first and second drive tube control signals ngate and pgate are at a logic high level, the drive tube MP1 is in a shut-off state, the drive tube MN1 is in a conducting state, and the power tube Q1 is in a shut-off state.

FIG3 shows a working timing diagram of multiple charging control related signals shown in FIG2. As shown in FIG3, when the power supply state indication signal VCC_low is at a logic high level, it indicates that the self-power supply of the control chip 202 is insufficient. When the power tube control signal pwm is at a logic low level, the demagnetization state indication signal dem is at a logic low level and needs to charge the chip power supply capacitor Cvcc after a delay of a period of time. When the input voltage indication signal HighLine is at a logic low level, it indicates that the AC input voltage AC is a low voltage, and the control drive tube NM1 and the switch tube M2 are in the off state, so that the AC input voltage AC charges the base of the power tube Q1 via the chip startup resistor R1, and after the power tube Q1 changes from the off state to the on state as its base voltage increases, the AC input voltage AC charges the chip power supply capacitor Cvcc via the power tube Q1 and the diode D1 (that is, the charging current I1 charges the chip power supply capacitor Cvcc). At this time, although the withstand voltage between the emitter and the collector of the power tube Q1 is small, since the AC input voltage AC is a low voltage, the power tube Q1 will not be broken down and damaged. When the input voltage indication signal HighLine is at a logic high level, it indicates that the AC input voltage AC is a high voltage, the charging switch control signal charge is at a logic high level, the charging control switch circuit is in an on state, the base of the power tube Q1 is short-circuited to the chip power supply capacitor Cvcc, and the AC input voltage AC charges the chip power supply capacitor Cvcc via the chip startup resistor R1 and the charging control switch circuit. At this time, the withstand voltage between the collector and the base of the power tube Q1 is relatively large, and the power tube Q1 will not be broken down and damaged.

FIG4 shows an example implementation circuit diagram of the charging control module shown in FIG2. In the charging control module 2028 shown in FIG4, resistors R2, R3, R4, R5, R6 and switch tubes MP2, MP3, MP4, MN3 form a charging control switch circuit; switch tubes MN3 and MP4 and resistors R4, R5, R6 form a control circuit for controlling the on and off of switch tubes MP2 and MP3; when switch tubes MP2 and MP3 are in the on state, the charging current I2 charges the chip power supply capacitor Cvcc via the chip startup resistor R1, resistor R2, switch tubes MP2 and MP3, and resistor R3; when switch tubes MP2 and MP3 are in the off state, the charging current I1 charges the charging power supply capacitor Cvcc via diode D1.

As shown in FIG4 , in some embodiments, the charging control module 2028 is further configured to: generate a demagnetization end indication signal dem_b indicating whether a predetermined time has passed since the demagnetization end moment of the secondary winding Ns of the transformer T based on the demagnetization state indication signal dem (for example, the switch tubes MP5 and MN4, the resistor R7, and the capacitor C0 form a delay circuit for generating the demagnetization end indication signal dem_b based on the demagnetization state indication signal dem); generate a charging requirement indication signal char_req indicating whether the chip power supply capacitor Cvcc needs to be charged based on the power tube control signal pwm, the demagnetization end indication signal dem_b, and the power supply state indication signal VCC_low (for example, by comparing the inverted signal of the power tube control signal pwm with the demagnetization end indication signal dem_b); A logic AND operation is performed on the demagnetization end indication signal dem_b to generate a transformer state indication signal state representing whether a predetermined time has passed since the demagnetization end moment of the secondary winding Ns of the transformer T while the power tube Q1 is in the off state; a charging requirement indication signal char_req is generated by performing a logic AND operation on the transformer state indication signal state and the power supply state indication signal VCC_low; and a first drive tube control signal ngate is generated based on the power tube control signal pwm and the charging requirement indication signal char_req (for example, the first drive tube control signal ngate is generated by performing a logic AND operation on the inverted signal of the power tube control signal pwm and the inverted signal of the charging requirement indication signal char_req).

As shown in FIG. 4 , in some embodiments, the charging control module 2028 is further configured to generate a charging switch control signal charge by performing a logic AND operation on an inverted signal of the input voltage indication signal Highline and the charging demand indication signal char_req.

As shown in FIG. 4 , in some embodiments, the charging control module 2028 is further configured to: during the startup process of the flyback switching power supply 200, generate a power-ready signal PG based on the chip power supply voltage VCC on the chip power supply capacitor Cvcc, and control the charging control switch circuit to change from an on state to an off state when the power-ready signal PG changes from a logic low level to a logic high level.

As shown in FIG4 , in some embodiments, during the startup process of the flyback switching power supply 200, the working principle of the charging control module 2028 is as follows: the chip power supply voltage VCC on the chip power supply capacitor Cvcc is 0V, the power-ready signal PG is at a logic low level, the driving tubes MP1 and MN1 and the switch tubes M2, MN3, and MP4 are all in the off state, the switch tubes MP2 and MP3 are in the on state, the chip power supply capacitor Cvcc is short-circuited to the chip startup resistor R1, and the charging current I2 directly charges the chip power supply capacitor Cvcc via the charging control switch circuit; when the chip charging voltage VCC on the chip power supply capacitor Cvcc is greater than the UVLO threshold of the control chip 202, the power-ready signal PG changes from a logic low level to a logic high level, the switch tube MN3 changes from an off state to an on state, so that the resistor R4 is grounded, which causes the switch tube MP4 to change from an off state to an on state, and the switch tube MP4 changes from an off state to an on state, which causes the switch tubes MP2 and MP3 to change from an on state to an off state, thereby completing the charging of the chip power supply capacitor Cvcc.

As shown in FIG4 , in some embodiments, during the normal operation of the flyback switching power supply 200 , the working principle of the charging control module 2028 is as follows: when the power supply status indication signal VCC_low is at a logic high level, it indicates that the chip power supply capacitor Cvcc needs to be charged; if the input voltage indication signal HighLine is at a logic low level, indicating that the AC input voltage AC is a low voltage, the charging switch control signal charge is at a logic low level, the switch tubes M2 and MN3 are in an off state, the drive tubes MP1 and MN1 are in an off state, and after the power tube Q1 changes from an off state to an on state, the charging current I1 charges the chip power supply capacitor Cvcc via the diode D1; if the input voltage indication signal HighLine is at a logic high level, indicating that the AC input voltage AC is a high voltage, the charging switch control signal charge is at a logic high level, the switch tubes MN3 and MP4 are in an off state, the switch tubes MP2 and MP3 are in an on state, the chip power supply capacitor Cvcc is short-circuited to the chip startup resistor R1, and the charging current I2 charges the chip power supply capacitor Cvcc via the charging control switch circuit.

It should be understood by those skilled in the art that the control circuit according to the embodiment of the present invention can be used not only in a flyback switching power supply, but also in a switching power supply adopting various architectures such as forward, buck, or boost. In addition, not only can the output voltage feedback signal FB be obtained by sampling the system output voltage Vo of the flyback switching power supply 100 by using the auxiliary winding Naux of the transformer T, but also the output voltage feedback signal FB can be obtained from the secondary side of the transformer T by using feedback devices such as an optocoupler.

The present invention can be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithms described in the specific embodiments can be modified, and the system architecture does not depart from the basic spirit of the present invention. Therefore, the current embodiments are regarded as exemplary and non-restrictive in all aspects, and the scope of the present invention is defined by the appended claims rather than the above description, and all changes falling within the meaning and equivalent scope of the claims are thus included in the scope of the present invention.

Claims (11)

1. A control circuit for use in a switching power supply, wherein the switching power supply comprises a chip start-up resistor and a chip supply capacitor, the control circuit comprising a charge control switching circuit and being configured to:

And in the starting process of the switching power supply, controlling the charging control switching circuit to be in a conducting state, so that the alternating-current input voltage of the switching power supply charges the chip power supply capacitor through the chip starting resistor and the charging control switching circuit.

2. The control circuit of claim 1, wherein the switching power supply further comprises a power tube, and the control circuit is further configured to:

In the normal working process of the switching power supply, under the condition that the power tube is in an off state and the chip power supply voltage on the chip power supply capacitor is smaller than a preset power supply threshold value, if the alternating current input voltage is larger than or equal to the preset input threshold value, the charging control switching circuit is controlled to be in a conducting state, so that the alternating current input voltage charges the chip power supply capacitor through the chip starting resistor and the charging control switching circuit, otherwise, a first driving tube connected between the base electrode of the power tube and the reference ground is controlled to be changed from the conducting state to the off state, so that the alternating current input voltage charges the base electrode of the power tube through the chip starting resistor, and after the power tube is changed from the off state to the conducting state along with the rising of the base electrode voltage, the alternating current input voltage charges the chip power supply capacitor through the power tube.

3. The control circuit of claim 1, further configured to:

During start-up of the switching power supply, a power supply ready signal is generated based on a chip supply voltage on the chip supply capacitor, and the charge control switching circuit is controlled to change from an on state to an off state when the power supply ready signal changes from a logic low level to a logic high level.

4. The control circuit of claim 2, the switching power supply further comprising a transformer, the power tube connected between a primary winding of the transformer and a reference ground, the control circuit further configured to:

Generating a power supply state indication signal representing whether the chip power supply voltage on the chip power supply capacitor is smaller than the preset power supply threshold value based on the chip power supply voltage on the chip power supply capacitor;

Generating a first driving tube control signal for controlling the on and off of the first driving tube based on a power tube control signal for controlling the on and off of the power tube, a demagnetizing state indication signal for indicating whether a secondary winding of the transformer is in a demagnetizing state, and the power supply state indication signal; and

And generating a charging switch control signal for controlling the on and off of the charging control switch circuit based on the power tube control signal, the demagnetizing state indication signal, the power supply state indication signal and an input voltage indication signal representing whether the alternating current input voltage is greater than or equal to the preset input threshold value.

5. The control circuit of claim 4, further configured to:

Generating a demagnetization end indication signal indicating whether a predetermined time has elapsed from a demagnetization end time of a secondary winding of the transformer based on the demagnetization state indication signal;

Generating a charging demand indication signal representing whether the chip power supply capacitor needs to be charged or not based on the power tube control signal, the demagnetization end indication signal and the power supply state indication signal; and

And generating the first driving tube control signal based on the power tube control signal and the charging demand indication signal.

6. The control circuit of claim 5, further configured to:

Generating a transformer state indicating signal representing whether the predetermined time has elapsed from the demagnetization end time of the secondary winding of the transformer while the power tube is in an off state by performing a logical AND operation on the inverted signal of the power tube control signal and the demagnetization end indicating signal;

generating the charging demand indication signal by performing a logical AND operation on the transformer state indication signal and the power supply state indication signal; and

And generating the first driving tube control signal by performing logical AND operation on the inverted signal of the power tube control signal and the inverted signal of the charging demand indication signal.

7. The control circuit of claim 6, further configured to:

The charge switch control signal is generated by performing a logical AND operation on the inverted signal of the input voltage indication signal and the charge demand indication signal.

8. The control circuit of claim 4, further configured to:

and generating a switching tube control signal for controlling on and off of a switching tube connected between an emitter of the power tube and a reference ground based on the power tube control signal, the demagnetizing state indication signal, the power supply state indication signal and the input voltage indication signal.

9. The control circuit of claim 4, further configured to:

And generating a second driving tube control signal for controlling the on and off of a second driving tube connected between the base electrode of the power tube and the chip power supply capacitor based on the power tube control signal.

10. The control circuit of claim 4, further configured to:

Generating the power tube control signal based on an output voltage feedback signal representative of a system output voltage of the switching power supply and a primary current detection signal representative of a primary current flowing through a primary winding of the transformer; and

The demagnetizing state indication signal and the input voltage indication signal are generated based on the output voltage feedback signal.

11. A switching power supply comprising the control circuit of any one of claims 1 to 10.