阅读说明：本技术 用于开关电源的短路保护电路、芯片及系统 (Short-circuit protection circuit, chip and system for switching power supply ) 是由 李瑞平 许锦龙 刘彬 池伟 于 2021-02-05 设计创作，主要内容包括：本发明公开了一种用于开关电源的短路保护电路、芯片及系统,所述短路保护电路包括：采集模块,用于采集输入电压,并根据所述输入电压生成第一电压；发生模块,用于根据基准电压产生第二电压；比较模块,用于比较所述第一电压和所述第二电压的大小；以及输出模块,用于当所述开关电源短路时根据所述比较模块的比较结果输出控制信号以控制外部功率管。本发明通过在检测到输出短路时,根据输入电压的大小调整打嗝占空比,实现高电压输入时不会出现能量损耗大的情况；同时低电压输入时,可以带载启动或短路撤销后自动恢复输出。(The invention discloses a short-circuit protection circuit, a chip and a system for a switching power supply, wherein the short-circuit protection circuit comprises: the acquisition module is used for acquiring input voltage and generating first voltage according to the input voltage; the generating module is used for generating a second voltage according to the reference voltage; the comparison module is used for comparing the first voltage with the second voltage; and the output module is used for outputting a control signal according to the comparison result of the comparison module when the switching power supply is in short circuit so as to control the external power tube. According to the invention, when the output short circuit is detected, the hiccup duty ratio is adjusted according to the magnitude of the input voltage, so that the condition of large energy loss can not occur during high-voltage input; meanwhile, when low voltage is input, the output can be automatically recovered after load starting or short circuit cancellation.)

1. A short-circuit protection circuit for a switching power supply, the short-circuit protection circuit comprising:

the acquisition module is used for acquiring input voltage and generating first voltage according to the input voltage;

the generating module is used for generating a second voltage according to the reference voltage, wherein the second voltage is a sawtooth voltage with a preset period;

the comparison module is used for comparing the first voltage with the second voltage; and

the output module is used for outputting a control signal according to the comparison result of the comparison module when the switching power supply is short-circuited so as to control an external power tube;

the comparison result comprises a first comparison result that the first voltage is greater than the second voltage in a first time period of the preset cycle, and the output module outputs a first control signal in the first time period according to the first comparison result to indicate that the external power tube does not work;

the comparison result further comprises a second comparison result that the first voltage is smaller than the second voltage in a second time period of the preset cycle, and the output module outputs a second control signal in the second time period according to the second comparison result to indicate the external power tube to work, wherein the preset cycle consists of the first time period and the second time period; and

the duration of the second time period decreases as the first voltage increases, wherein the larger the first voltage, the smaller the hiccup duty cycle, and the smaller the first voltage, the larger the hiccup duty cycle.

2. The short-circuit protection circuit for a switching power supply according to claim 1, wherein the first voltage varies linearly with the input voltage.

3. The short-circuit protection circuit for a switching power supply according to claim 1, further comprising a detection module connected to the output module for detecting whether there is a short circuit in the switching power supply, wherein: when short circuit exists, the detection module outputs a low level signal, and when short circuit does not exist, the detection module outputs a high level signal.

4. The short-circuit protection circuit for a switching power supply according to claim 1, wherein the comparison module outputs a low level signal when the first voltage is greater than the second voltage; and when the first voltage is smaller than the second voltage, the comparison module outputs a high level signal.

5. The short-circuit protection circuit for switching power supply according to claim 4, wherein when the comparison module outputs a low level signal, the output module outputs a high level signal to control the external power transistor not to operate; and when the comparison module outputs a high level signal, the output module outputs a low level signal to control the external power tube to work.

6. A short-circuit protection method for a switching power supply, the method comprising:

collecting an input voltage, and generating a first voltage according to the input voltage;

generating a second voltage according to the reference voltage, wherein the second voltage is a sawtooth voltage with a preset period;

comparing the first voltage and the second voltage; and

when the switching power supply is in short circuit, outputting a control signal according to a comparison result of the first voltage and the second voltage to control an external power tube;

the comparison result comprises a first comparison result that the first voltage is greater than the second voltage in a first time period of the preset period, and a first control signal is output in the first time period according to the first comparison result to indicate that the external power tube does not work;

the comparison result further comprises a second comparison result that the first voltage is smaller than the second voltage in a second time period of the preset cycle, and a second control signal is output in the second time period according to the second comparison result to indicate that the external power tube works, wherein the preset cycle consists of the first time period and the second time period; and

the duration of the second period of time decreases as the first voltage increases.

7. A switching power supply chip characterized by comprising the short-circuit protection circuit of any one of claims 1 to 5.

8. The switching power supply chip of claim 7, further comprising a power supply module and a power tube module, wherein:

the power supply module is respectively connected with the acquisition module, the generation module, the comparison module and the detection module and is used for supplying power to the acquisition module, the generation module, the comparison module and the detection module; and

the power tube module is connected with the output module and used for controlling the power tubes in the power tube module to work or stop working according to the control signal of the output module.

9. A switching power supply system characterized in that it comprises a short-circuit protection circuit according to any one of claims 1 to 5.

Technical Field

The invention relates to the field of power supply chips, in particular to a short-circuit protection circuit, a chip and a system of a switching power supply.

Background

When the switching power supply system detects an output short circuit, short circuit protection can be performed, and various short circuit protection methods can be used, such as common methods of short circuit current limiting output, short circuit turn-off output, short circuit hiccup output and the like.

The short-circuit current-limiting output mode is that when the output short circuit is detected, the output current is limited, and the power supply system equivalently works in a constant current mode and can play a role in protecting the system. However, in order to ensure that the system can be started normally or the short circuit is recovered, the current limiting value is usually set to be large, so that the energy loss during short circuit is high, and certain requirements are imposed on peripheral devices.

The short-circuit shutdown output is a mode that directly shuts down the output when an output short circuit is detected. When the power supply system is started, the output voltage is low, and the system can be considered to be in a short-circuit state. Therefore, the short-circuit shutdown output has strict requirements on starting, a power supply system is generally required to be started and then output to load, and a lot of limitations are brought to application.

The way to short the hiccup output is a compromise. After detecting the output short circuit, the method enters a hiccup output mode, namely, the method outputs the output for a period of time and stops working, so that on one hand, the loss can be reduced to a lower value, and on the other hand, the output mode is turned off in a shorter path, and the method can be started with a better light load.

However, in the conventional short-circuit hiccup output mode, it is defined that in one hiccup period, the ratio of the duration of the hiccup output (during hiccup) to the total duration of the last hiccup period is the hiccup duty ratio, and in general, the hiccup duty ratio is a constant value in the circuit, i.e. it does not change with the change of the input voltage. Then at high voltage inputs the energy delivered to the output of the switching power supply system during hiccup is high and at low voltage inputs the energy delivered to the output during hiccup is low. Therefore, when the low voltage is input, the problem that the starting cannot be successful due to insufficient energy in the starting process with the load is possible; when high voltage is input, because the hiccup duty ratio is the definite value, although being in the output protection of short circuit hiccup, the short-circuit loss is great, causes the energy waste on the one hand, and on the other hand has the threat to power supply system's stability.

Disclosure of Invention

The invention provides a short-circuit protection circuit, a chip and a system for a switching power supply, wherein when an output short circuit is detected, the hiccup duty ratio is adjusted according to the magnitude of input voltage, so that the condition of large energy loss can not occur during high-voltage input; meanwhile, when low voltage is input, the output can be automatically recovered after load starting or short circuit cancellation.

An embodiment of the present invention provides a short-circuit protection circuit for a switching power supply, the short-circuit protection circuit including: the acquisition module is used for acquiring input voltage and generating first voltage according to the input voltage; the generating module is used for generating a second voltage according to the reference voltage, wherein the second voltage is a sawtooth voltage with a preset period; the comparison module is used for comparing the first voltage with the second voltage; the output module is used for outputting a control signal according to the comparison result of the comparison module so as to control the external power tube; the output module is configured to output a first control signal in a first time period according to the first comparison result to indicate that the external power transistor does not work when the switching power supply is short-circuited; the comparison result further comprises a second comparison result that the first voltage is smaller than the second voltage in a second time period of the preset cycle, and the output module outputs a second control signal in the second time period according to the second comparison result to indicate the external power tube to work, wherein the preset cycle consists of the first time period and the second time period; and the duration of the second period of time decreases with increasing first voltage. Wherein the sum of the first time period and the second time period is fixed (i.e. the sum of the first time period and the second time period is equal to a preset period). The duration of the second period of time decreases with increasing said first voltage, while the duration of the first period of time increases with increasing said first voltage.

Further, the first voltage varies linearly with the input voltage.

Further, the circuit further comprises a detection module connected to the output module, for detecting whether there is a short circuit in the switching power supply, wherein: when short circuit exists, the detection module outputs a low level signal, and when short circuit does not exist, the detection module outputs a high level signal.

Further, when the first voltage is greater than the second voltage, the comparison module outputs a low level signal; and when the first voltage is smaller than the second voltage, the comparison module outputs a high level signal.

Further, when the comparison module outputs a low level signal, the output module outputs a high level signal to control the external power tube not to work; and when the comparison module outputs a high level signal, the output module outputs a low level signal to control the external power tube to work.

Further, the larger the first voltage is, the smaller the hiccup duty cycle is after the second voltage is generated according to the reference voltage; and the smaller the first voltage, the larger the hiccup duty cycle.

An embodiment of the present invention further provides a short-circuit protection method for a switching power supply, including: collecting an input voltage, generating a first voltage according to the input voltage, and generating a second voltage according to a reference voltage, wherein the second voltage is a sawtooth wave voltage with a preset period; comparing the first voltage and the second voltage; and the control circuit is used for outputting a control signal according to the comparison result of the comparison module when the switching power supply is short-circuited so as to control an external power tube; the comparison result comprises a first comparison result that the first voltage is greater than the second voltage in a first time period of the preset period, and a first control signal is output in the first time period according to the first comparison result to indicate that the external power tube does not work; the comparison result further comprises a second comparison result that the first voltage is smaller than the second voltage in a remaining second time period of the preset period, and a second control signal is output in the second time period according to the second comparison result to indicate the external power tube to work, wherein the preset period consists of the first time period and the second time period; and the duration of the second period of time decreases with increasing first voltage.

The embodiment of the invention also provides a switching power supply chip which comprises the short-circuit protection circuit provided by any one of the embodiments of the invention.

Further, the switching power supply chip further includes a power supply module and a power tube module, wherein: the power supply module is respectively connected with the acquisition module, the generation module, the comparison module and the detection module and is used for supplying power to the acquisition module, the generation module, the comparison module and the detection module; the power tube module is connected with the output module and used for controlling the power tubes in the power tube module to work or stop working according to the control signal of the output module.

Embodiments of the present invention also provide a switching power supply system including a short-circuit protection circuit as provided in any of the embodiments of the present invention.

According to the invention, when an output short circuit is detected, the hiccup duty ratio is adjusted according to the magnitude of the input voltage, so that the hiccup duty ratio is increased when a low voltage is input, and each hiccup output has enough energy to be transmitted to the output end of the switching power supply system to start with load; meanwhile, the hiccup duty ratio is reduced when high voltage is input, so that the energy loss during short circuit is reduced, the stable work of the system is facilitated, and the on-load starting can still be realized.

Drawings

The technical solution and other advantages of the present invention will become apparent from the following detailed description of specific embodiments of the present invention, which is to be read in connection with the accompanying drawings.

Fig. 1 is a block diagram of a short-circuit protection circuit according to an embodiment of the present invention.

Fig. 2 is a schematic connection diagram of the short-circuit protection circuit shown in fig. 1.

Fig. 3 is a schematic diagram illustrating a relationship between the input voltage VIN collected by the collecting module of the short-circuit protection circuit shown in fig. 2 and the generated first voltage VA.

Fig. 4 is a waveform diagram of the second voltage VB generated by the generating module of the short-circuit protection circuit shown in fig. 2.

Fig. 5A is a relationship diagram of the first voltage VA, the second voltage VB and the third voltage VC output by the comparing module of the short-circuit protection circuit shown in fig. 2.

Fig. 5B is another relationship diagram of the first voltage VA, the second voltage VB and the third voltage VC output by the comparing module of the short-circuit protection circuit shown in fig. 2.

Fig. 6 is a relationship diagram of the third voltage VC of the short-circuit protection circuit shown in fig. 2, the fourth voltage VD output by the detection module, and the control signal VE output by the output module.

Fig. 7 is a flowchart of a short-circuit protection method of the short-circuit protection circuit shown in fig. 2.

Fig. 8 is a block diagram showing a configuration of a switching power supply chip using the short-circuit protection circuit shown in fig. 2.

Fig. 9 is a schematic connection diagram of a switching power supply chip using the short-circuit protection circuit shown in fig. 2.

Fig. 10 is a schematic connection diagram of a switching power supply system using the switching power supply chip shown in fig. 8.

Fig. 11A is a waveform diagram of an output voltage VSW at the time of short-circuiting hiccup output of the switching power supply chip of the switching power supply system shown in fig. 10.

Fig. 11B is a partially enlarged view of a waveform of the output voltage VSW at the time of short-circuiting hiccup output of the switching power supply chip of the switching power supply system shown in fig. 11A.

Fig. 12A is another waveform diagram of the output voltage VSW at the time of short-circuiting hiccup output of the switching power supply chip of the switching power supply system shown in fig. 10.

Fig. 12B is a partially enlarged view of a waveform of the output voltage VSW at the time of short-circuiting hiccup output of the switching power supply chip of the switching power supply system shown in fig. 12A.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

Specifically, referring to fig. 1, the short-circuit protection circuit 100 for a switching power supply provided in the present embodiment includes an acquisition module 110, a generation module 120, a comparison module 130, a detection module 140, and an output module 150. The acquisition module 110 acquires an input voltage VIN and generates a first voltage VA according to the input voltage VIN. The generating module 120 is configured to generate the second voltage VB according to the reference voltage VREF. The comparing module 130 is connected to the generating module 120 and the collecting module 110, respectively, and configured to compare the first voltage VA and the second voltage VB. The detection module 140 is connected to the output module 150 and an external load circuit, and detects whether a short circuit exists in the switching power supply. When the switching power supply is short-circuited, the output module 150 outputs a control signal to control a power tube module 160 (see fig. 8) according to the comparison result of the comparison module 130.

The short-circuit protection circuit 100 provided in this embodiment can solve the problems that the conventional switching power supply chip with the short-circuit hiccup output function is difficult to start when a low voltage is input, and has a large energy loss when a high voltage is input. Specifically, when the switching power supply system detects that the output end has a short circuit, the switching power supply chip operates in a hiccup mode, where the hiccup mode is that the switching power supply chip periodically operates for a period of time (operating time) and then stops for a period of time (stopping time). The hiccup duty ratio is the ratio of the working time of the switching power supply chip to the sum of the working time and the stopping time. Therefore, the larger the hiccup duty ratio is, the longer the operating time of the switching power supply chip is, and the shorter the stop time is. In the embodiment, by detecting the input voltage VIN at the input end of the switching power supply system, when the input voltage VIN is a low voltage, the hiccup duty ratio is increased to increase the working time of the switching power supply chip, so that sufficient energy is transmitted to the output end of the switching power supply system at each hiccup output when the low voltage is input, and the situation that the normal output cannot be recovered due to the incapability of load starting or short circuit withdrawal is prevented; meanwhile, when the input voltage VIN is high voltage, the hiccup duty ratio is reduced to reduce the working time of the switching power supply chip and increase the stopping time, so that the energy loss during short circuit is reduced, the working stability of the switching power supply system is facilitated, and the on-load starting can still be carried out.

The structure and function of each module will be described in detail below with reference to fig. 2 to 6.

The acquisition module 110 includes: resistors R1, R2, R3, R4, R5, R6, and an operational amplifier OP 1. One end of the resistor R2 receives the input voltage VIN, the other end of the resistor R2 is connected to one end of the resistor R1, and the other end of the resistor R1 is grounded. One end of the resistor R4 is connected to the resistor R2 and the resistor R1, respectively, and the other end of the resistor R4 is connected to one end of the resistor R3 and the first input end of the operational amplifier OP1, respectively. The other end of resistor R3 receives a reference voltage VREF. A second input terminal of the operational amplifier OP1 is connected to one terminal of the resistor R5 and one terminal of the resistor R6, respectively, the other terminal of the resistor R5 is grounded, and the other terminal of the resistor R6 is connected to the output terminal of the operational amplifier OP 1. The output terminal of the operational amplifier OP1 outputs a first voltage VA. The first power supply terminal of the operational amplifier OP1 is connected to the supply voltage VDD. The second power supply terminal of the operational amplifier OP1 is grounded.

The acquisition module 110 is configured to acquire an input voltage VIN, and perform potential translation on the input voltage VIN after the input voltage VIN is proportionally attenuated. As shown in fig. 2, the reference voltage VREF provides a high-precision reference voltage for the circuits of the switching power supply chip, and at the same time, the resistors R1 to R6 are reasonably arranged so that the first voltage VA ranges from, for example, 3.6V to 3.8V when the input voltage VIN ranges from, for example, 24V to 72V, as shown in fig. 3. Specifically, the first voltage VA is calculated by the following formula 1:

note that the reference voltage VREF must be set. If the reference voltage VREF does not exist, the first voltage VA only changes in proportion near 0V, so that the voltage value of the first voltage VA is low and can be identified by the comparison module 130 only through once amplification; otherwise, the magnitude of the first voltage VA is too small, and the comparing module 130 cannot output a reasonable hiccup duty cycle signal. The first voltage VA with respect to the input voltage VIN is shown in fig. 3. Specifically, the first voltage VA varies linearly with the input voltage VIN. Therefore, the variation of the first voltage VA may reflect the variation of the input voltage VIN, i.e. the larger the first voltage VA, the larger the input voltage VIN, and vice versa.

The generation module 120 includes: a current source IS1, a capacitor C1, a field effect transistor M1, resistors R8 and R9, and an operational amplifier OP 2. One end of the current source IS1 IS connected to the supply voltage VDD, and the other end IS connected to one end of the capacitor C1 and the drain of the field effect transistor M1, respectively. The other end of the capacitor C1 is grounded. A first input terminal of the operational amplifier OP2 is connected to the drain of the field effect transistor M1, a second input terminal of the operational amplifier OP2 is connected to one end of the resistor R8 and one end of the resistor R9, respectively, and a first input terminal of the operational amplifier OP2 receives a second voltage VB. The other end of the resistor R8 receives a reference voltage VREF, and the other end of the resistor R9 is connected to the output terminal of the operational amplifier OP2 and the gate of the field effect transistor M1. The source of the field effect transistor M1 is grounded. The first power supply terminal of the operational amplifier OP2 is connected to the supply voltage VDD. The second power supply terminal of the operational amplifier OP2 is grounded.

The generating module 120 generates a second voltage VB according to the reference voltage VREF, wherein the second voltage VB is a sawtooth voltage with a preset period T, as shown in fig. 4. Referring to fig. 2 again, the operational amplifier OP2 of the generating module 120 can output rail-to-rail, that is, the high level can reach the supply voltage VDD, and the low level can reach 0V, so that the peak value VB1 and the valley value VB2 of the sawtooth wave VB (the second voltage VB) generated by the generating module 120 can be obtained according to the following formula 2 and formula 3, respectively:

equation 2:

equation 3:

meanwhile, because the discharge loop formed by the field effect transistor M1 and the capacitor C1 has small resistance, compared with the charging time, the discharging time of the capacitor C1 can be ignored. When the discharge time is neglected, the frequency f of the sawtooth wave of the second voltage VB is obtained according to the following equation 4:

wherein IS a current value of the current source IS1, C IS a capacitance value of the capacitor C1, and VB1 and VB2 are a peak value VB1 and a valley value VB2 of the sawtooth wave VB generated by the generating module 120, respectively. In addition, the preset period T can be obtained by inverting the calculated frequency f.

The comparison module 130 includes a comparator COMP 1. A first input terminal of the comparator COMP1 is connected to a first input terminal of the operational amplifier OP2 of the generating module 120, and a second input terminal of the comparator COMP1 is connected to an output terminal of the operational amplifier OP1 of the acquiring module 110. A first power supply terminal of the comparator COMP1 is connected to a supply voltage VDD. The second power terminal of the comparator COMP1 is grounded. An output end of the comparator COMP1 outputs a third voltage VC.

The comparing module 130 is connected to the generating module 120 and the collecting module 110, respectively, and configured to compare the first voltage VA and the second voltage VB. Specifically, when the second voltage VB is greater than the first voltage VA, the third voltage VC of the comparing module 130 outputs a high level; when the second voltage VB is smaller than the first voltage VA, the third voltage VC outputs a low level. The critical condition is negligible when the second voltage VB is equal to the first voltage VA. The comparing module 130 is configured to compare the level heights of the second voltage VB and the first voltage VA to generate a rectangular wave (i.e., a third voltage) VC with different hiccup duty ratios. The hiccup duty ratio D of the rectangular wave VC is obtained according to the following equation 5:

specifically, if the first voltage VA is greater than the peak value VB1 of the second voltage VB, the hiccup duty cycle D of the rectangular wave VC is 0 (VA is always smaller than VB1 by reasonable design). When the first voltage VA is smaller than the valley VB2 of the second voltage VB, the duty ratio is1 (VA can be reasonably designed to be always larger than the valley VB 2). As can be seen from the above equation 5, the smaller the first voltage VA, the larger the hiccup duty ratio D; while the larger the first voltage VA, the smaller the hiccup duty cycle D. Since the first voltage VA and the input voltage VIN are in a linear relationship (as shown in fig. 3), it can be understood that the smaller the input voltage VIN is, the larger the hiccup duty ratio D is, the longer the time that the switching power supply chip works in the hiccup period (i.e., the preset period T) is, and the more the switching times of the power tube in the switching power supply chip are; conversely, the larger the input voltage VIN is, the smaller the hiccup duty ratio D is, the shorter the time that the switching power supply chip operates in the hiccup period is, and the fewer the switching times of the power tube in the switching power supply chip are. The duty ratio of the rectangular wave VC output at different first voltages VA (i.e., different input voltages VIN) is as shown in fig. 5A and 5B, where the first voltage VA voltage in fig. 5A is small and the first voltage VA voltage in fig. 5B is high. It is understood that the hiccup duty ratio D in fig. 5A is larger than that of fig. 5B, i.e., the on time of the switching power supply chip at the time of the low voltage input (i.e., the time period during which the rectangular wave VC outputs the high level in fig. 5A and 5B) is longer than that at the time of the high voltage input.

The detection module 140 includes: comparator COMP2, and resistor R10 and resistor R11. A first input end of the comparator COMP2 is connected to an external feedback circuit, and is used for detecting whether an output end of an external switching power supply system is short-circuited. A second input end of the comparator COMP2 is connected to one end of the resistor R10 and one end of the resistor R11, respectively. The other end of the resistor R10 receives a reference voltage VREF, and the other end of the resistor R11 is grounded. A first power supply terminal of the comparator COMP2 is connected to a supply voltage VDD. The second power terminal of the comparator COMP2 is grounded. An output end of the comparator COMP2 outputs a fourth voltage VD.

The detection module 140 is used for detecting whether a short circuit phenomenon exists at the output end. The input voltage VFB is a feedback pin voltage, and during normal operation, the voltage is equal to VREF, and when the input voltage VFB is short-circuited or just started, the input voltage VFB is very low, and if the input voltage VFB is lower than a preset value, the input voltage VFB can be considered as a short circuit. In this embodiment, as shown in fig. 2, if VFB < VREF × R11/(R11+ R10), the output is considered to be short-circuited. When the output end of the switching power supply system is short-circuited, the fourth voltage VD of the detection module 140 is a low level; when the switching power supply system normally works, the fourth voltage VD is at a high level.

The output module 150 includes: inverters N1 and N2, and gate a 1. The input end of the inverter N1 is connected to the output end of the comparator COMP1 of the comparing module 130. The input end of the inverter N2 is connected to the output end of the comparator COMP2 of the detection module 140. The output end of the inverter N1 is connected with the first input end of the AND gate A1, and the output end of the inverter N2 is connected with the second input end of the AND gate A1. The output of the and gate a1 outputs a control signal VE to the power tube module 160 (shown in fig. 8).

In this embodiment, the output module 150 outputs a control signal VE to control the power tube module 160 according to the comparison result of the comparison module 130 only when the output terminal of the switching power supply system is short-circuited, that is, the fourth voltage VD of the detection module 140 outputs a low level. Specifically, when the third voltage VC output by the comparing module 130 and the fourth voltage VD output by the detecting module 140 are at a low level at the same time, the control signal VE outputs a high level; when the third voltage VC outputs a high level and the fourth voltage VD outputs a low level, the control signal VE outputs a low level, which can be specifically seen in fig. 6. When the control signal VE outputs a high level, the power transistor module 160 of the switching power supply chip completely turns off the power transistor; when the control signal VE outputs a low level, the power transistor module 160 operates normally, that is, during this time period, the power transistors in the power transistor module 160 start to operate according to a normal mode, that is, periodically turn on and off.

In addition, it can be understood that when there is no short circuit at the output terminal of the switching power supply system, that is, the fourth voltage VD of the detection module 140 outputs a high level, the control signal VE of the output module 150 always outputs a low level regardless of whether the third voltage VC output by the comparison module 130 is a high level or a low level, so as to control the power tube module 160 to operate normally, that is, to turn on and off periodically.

According to the embodiment of the invention, when it is detected that a short circuit exists at the output end of the switching power supply system (that is, the fourth voltage VD outputs a low level), the duration that the third voltage VC output by the comparison module 130 is a high level (that is, the hiccup duty ratio D is adjusted) is adjusted according to the magnitude of the input voltage VIN, so that the duration that the power tube in the power tube module 160 normally works is adjusted, and the purpose of controlling the output energy of the power tube is achieved. In the normal working time period, the power tube of the switching power supply chip can work according to the normal mode, namely, the power tube is continuously turned on and off.

Fig. 7 is a flowchart of a short-circuit protection method of the short-circuit protection circuit shown in fig. 2. When the switching power supply is short-circuited, that is, when the fourth voltage VD of the detection module 140 outputs a low level, the short-circuit protection method specifically includes the following steps:

step S701, collecting input voltage, and generating first voltage according to the input voltage.

Step S702, generating a second voltage according to the reference voltage, wherein the second voltage is a sawtooth voltage having a preset period.

Step S703 compares the first voltage and the second voltage.

Step S704, outputting a control signal to control the external power tube according to the comparison result of the comparison module.

Fig. 8 is a block diagram showing a configuration of a switching power supply chip 200 that uses the short-circuit protection circuit 100 shown in fig. 2. Fig. 9 is a schematic connection diagram of a switching power supply chip 200 using the short-circuit protection circuit 100 shown in fig. 2. As shown in fig. 8 and 9, the switching power supply chip 200 further includes a power supply module 170 and a power tube module 160, wherein the power supply module 170 is respectively connected to the acquisition module 110, the generation module 120, the comparison module 130 and the detection module 140, and is configured to provide a voltage VDD. The power tube module 160 is connected to the output module 150, and is configured to control a power tube in the power tube module 160 to operate or stop operating according to a control signal of the output module 150. The switching power supply chip 200 further includes a frequency compensation module 180, which is connected to the power transistor module 160 and is used to stabilize a control loop of the power supply chip.

The switching power supply chip 200 shown in fig. 8 and 9 can realize large hiccup duty ratio when short-circuit hiccup output is performed at low voltage input; when a high voltage is input, the hiccup duty ratio is small. The method has the advantages that when low voltage is input, the hiccup duty ratio is large, so that the power tube of the switching power supply chip is turned on for a plurality of times during the period, although the input voltage is low, the power tube of the switching power supply chip is turned on for a plurality of times, and the accumulated output energy can effectively solve the problem that the conventional short circuit hiccup circuit is difficult to start with load when the low voltage is input, namely the low voltage input load starting can be realized, and the output voltage can be automatically recovered even if the output end is connected with the load after the short circuit is cancelled; meanwhile, when high voltage is input, the hiccup duty ratio is small, so that the power tube of the switching power supply chip is less in opening times, although the input voltage is high, the accumulated output energy is smaller than that in a conventional short circuit hiccup mode, the loss is low, and even if the output end is connected with a load after short circuit cancellation, the output voltage can be automatically recovered.

Fig. 10 is a schematic connection diagram of a switching power supply system 300 using the switching power supply chip 200 shown in fig. 8. The first pin IN of the switching power supply chip 200 is connected to the input terminal VIN 1. One end of each of the capacitor CIN and the capacitor C2 is connected to the input end VIN1, and the other end is grounded to GND. The second pin FB of the switching power supply chip 200 is connected to one end of a capacitor CFF, one end of a resistor R2 and one end of a resistor R1, the other end of the resistor R1 is grounded GND, and the other ends of the capacitor CFF and the resistor R2 are connected to one end of an inductor L1 and an output terminal VOUT respectively. The other end of the inductor L1 is connected to the third pin SW of the switching power supply chip 200 and the cathode of the diode D1. The anode of the diode D1 is grounded. One end of each of the capacitor COUT and the capacitor C3 is connected to the output terminal VOUT, and the other end is connected to the GND. The first pin IN is used for providing an input voltage VIN to the switching power supply chip 200; the second pin FB is used for receiving a feedback voltage VFB to stabilize the output voltage of the output terminal VOUT, and detecting whether the switching power supply system 300 has a short circuit; and the third pin SW is for outputting a voltage VSW to supply energy to an external load.

Specifically, when the load is short-circuited and the input voltage VIN is different, the waveforms of the output voltage VSW of the switching power chip 200 are as shown in fig. 11A and 11B, and fig. 12A and 12B. Fig. 11A is a waveform of the output voltage VSW when the input voltage VIN is 24V, and fig. 12A is a waveform of the output voltage VSW when the input voltage VIN is 72V. Fig. 11B is a partially enlarged view of the waveform of the output voltage VSW when the input voltage VIN is 24V. Fig. 12B is a partially enlarged view of the waveform of the output voltage VSW when the input voltage VIN is 72V. As can be seen from fig. 11A to 12B, when short-circuiting or starting is performed, the duty ratio of the time during which the power tube normally operates in the same time interval (for example, in the interval of 0.00074s to 0.0008 s) at the time of low-voltage input (for example, 24V) is greater than the duty ratio of the time during which the power tube normally operates at the time of high-voltage input (for example, 72V) (that is, when short-circuiting or starting is performed, the number of times the power tube is turned on at the time of low-voltage input is greater than the number of times the power tube is turned on at the time of high-voltage input) at the time of low-voltage input), so that it is easier to start.

According to the short-circuit protection circuit, the chip and the system of the switching power supply, the hiccup duty ratio is adjusted through the size of the input voltage, the problems that the output is difficult to restore after the load starting or the short circuit canceling in the conventional short-circuit hiccup protection mode is carried out at the low voltage input, and the output short-circuit loss is large when the high voltage input is carried out can be solved, the hiccup duty ratio is increased when the low voltage input is carried out, so that enough energy is output during the hiccup duty ratio and is transmitted to the output end of the switching power supply system, and the load starting can be realized; meanwhile, the hiccup duty ratio is reduced when high voltage is input, so that the energy loss during short circuit is reduced, the stable work of the system is facilitated, and the on-load starting can still be realized.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

The short-circuit protection circuit, the chip and the system for the switching power supply provided by the embodiment of the present application are introduced in detail, a specific example is applied in the present application to explain the principle and the implementation manner of the present application, and the description of the above embodiment is only used to help understanding the technical scheme and the core idea of the present application; those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure as defined by the appended claims.