CN1152464C - DC/DC switching power supply soft start circuit with voltage compensation - Google Patents

Abstract

The invention belongs to the technical field of switching power supply design for portable electronic products, and is composed of four modules: charging timing and compensation voltage generating circuit, level shift circuit, overcurrent comparator and switching power supply; the invention can judge whether a current surge phenomenon occurs The threshold of is slowly increased with the charging time of the start-up process. Keep the charging process as stable as possible without multiple restarts. So that the electronic system will not be damaged.

Description

DC/DC switching power supply soft start circuit with voltage compensation

Technical Field The present invention belongs to the technical field of switching power supply design for portable electronic products, and in particular relates to the design of integrated control chips for switching power supplies.

BACKGROUND OF THE INVENTION There are various techniques for realizing the soft start of switching power supplies, but all of them have many deficiencies. Some soft-start circuits judge whether the current surge (or current overshoot) phenomenon occurs in the circuit, and give a fixed threshold. As long as the current exceeds this threshold, the soft-start circuit will output a control signal to cut off the charging current, and at the same time, the entire power supply will restart. Enter the boot state. The disadvantage of this method is that when the charging process reaches a certain stage and the charging current gradually rises to a certain level, it is easy to restart the power supply many times due to occasional overcurrent. For example, during the start-up process of a typical DC/DC switching power supply, it is easy to generate surge current, which may cause damage to the electronic system. Therefore, it is necessary and necessary to eliminate the possible overcurrent phenomenon during the start-up process of the power supply.

SUMMARY OF THE INVENTION The purpose of the present invention is to overcome the deficiencies of the prior art, and propose a DC/DC switching power supply soft start circuit using voltage compensation, which can make the threshold for judging whether a current surge occurs with the charging time of the starting process. increase slowly. Keep the charging process as stable as possible without multiple restarts. So that the electronic system will not be damaged.

A DC/DC switching power supply soft start circuit using voltage compensation proposed by the present invention is characterized in that it is composed of four modules: charging timing and compensation voltage generating circuit, level shift circuit, overcurrent comparator and switching power supply; The connection relationship is: the start signal EN1 is connected to the input port of the charging timing and compensation voltage generating circuit, the compensation voltage Vc output port of the charging timing and compensation voltage generating circuit is connected to the input terminal of the level shift circuit, the charging timing and compensation The soft-start failure indication signal F output port of the voltage generating circuit is connected to the input end of the switching power supply module, and the enable signal EN2 output port of the charging timing and compensation voltage generating circuit is connected to the input end of the overcurrent comparator; The ports of the output signals HL and LL are connected to the input terminals of the level shift circuit; the ports of the output signals A and B of the level shift circuit are connected to the two comparison signal input ports of the overcurrent comparator; The port of the output signal E is connected to the input terminal of the switching power supply; the charging timing and compensation voltage generation circuit, the level shift circuit and the overcurrent comparator module share the working voltage Vin1, and the input power supply voltage of the switching power supply module is Vin2;

Said charging timing and compensating voltage generating circuit are composed of current source I4, transistor m14 and transistor mx, transistor T4 and transistor T6, resistor R5, compensating resistor R6, resistor R8, resistor R10 and resistor R11, capacitor C2, inverter inv1 , composed of inverter inv2 and inverter inv3; its connection relationship is: one end of current source I4 is connected to the power supply 5V, and the other end is connected to the source of transistor m14; the gate of transistor m14 is connected to the output of inverter inv1 terminal, and the drain of transistor m14 is connected to one end of resistor R5; the start signal EN1 of this module is connected to the input terminal of inverter inv1; the collector of transistor T4 is connected to power supply 5V, and its emitter is connected to one end of resistor R11 , and its base is simultaneously connected to one end of the resistor R5, the input end of the inverter inv2, the emitter of the transistor T6, the drain of the transistor mx and one end of the capacitor C2; the collector of the transistor T6 is connected to one end of the resistor R8, Its base is connected to one end of the resistor R10; the other end of the resistor R10 is connected to a 2.5V reference voltage, and the other end of the resistor R8 is grounded; the source of the transistor mx is grounded, and its gate is connected to the output of the inverter inv1 end; the other end of the capacitor C2 is grounded; one end of the compensation resistor R6 is grounded, and the other end is connected to the other end of the resistor R11, and the output compensation voltage Vc is sent to the level shift circuit module; the output of the inverter inv2 is connected to the inverter inv3 The input terminal is connected to the enable signal EN2; the output terminal of the inverter inv3 is connected to the soft start failure indication signal F.

The feature of the present invention is that the adopted voltage compensation technology can make the threshold for judging whether a current surge phenomenon occurs slowly increase with the charging time in the starting process. Because in the switching power supply circuit, as the charging time increases, the current that charges the output capacitor through the inductor increases gradually. At this time, the voltage compensation technology in the present invention also slowly increases the threshold for judging whether the inductor current is overcurrent, so the present invention can keep the charging process as stable as possible without multiple restarts.

Description of drawings

Fig. 1 is a schematic diagram of the functional module structure of the present invention.

Fig. 2 is a schematic diagram of a structure embodiment of the soft start circuit of the present invention.

FIG. 3 is a schematic diagram of an embodiment of an overcurrent comparator in an embodiment of the present invention.

Figure 4 is a graph of the current surge and voltage overshoot generated during startup without a soft-start circuit.

FIG. 5 is a graph showing the variation of inductor current and output voltage with time during the startup process using the startup circuit of the present invention.

Detailed ways

A kind of DC/DC switching power supply soft-start circuit using voltage compensation designed by the present invention is described in detail as follows in combination with embodiments and accompanying drawings:

The structure designed by the present invention is shown in Fig. 1, and is made up of four modules of charging timing and compensation voltage generating circuit I, level shifting circuit II, overcurrent comparator III and switching power supply IV. The connection relationship is: the start signal EN1 is connected to the input port of the charging timing and compensation voltage generating circuit, the compensation voltage Vc output port of the charging timing and compensation voltage generating circuit is connected to the input terminal of the level shift circuit, and the charging timing and compensation voltage generating circuit The soft-start failure indication signal F output port of the circuit is connected to the input terminal of the switching power supply module, and the enable signal EN2 output port of the charging timing and compensation voltage generating circuit is connected to the input terminal of the overcurrent comparator; the signal HL of the switching power supply module And the LL output port is connected with the input terminal of the level shift circuit; the output signal A and B ports of the level shift circuit are connected with the two comparison signal input ports of the overcurrent comparator; the output signal E of the overcurrent comparator The port is connected to the input terminal of the switching power supply. The charging timing and compensation voltage generating circuit, the level shifting circuit and the overcurrent comparator module share the working voltage Vin1 (range 3.3-5V), while the input power supply of the switching power supply module is Vin2 (range 5.5-30V).

Working principle of the present invention is:

EN1 is the start signal, so that the charging timing and compensation voltage generating circuit starts to work, and the output compensation voltage Vc generated by the charging timing and compensation voltage generating circuit is input to the level shift circuit; at the same time, the charging timing and compensation voltage generating circuit generates an output signal F, It is the soft start failure indication signal. When the soft start fails, the output of the switching power supply is discharged to the ground and waits for restart; in addition, the charging timing and compensation voltage generation circuit outputs the enable signal EN2, which is input to the overcurrent comparator to control Overcurrent comparator is working or not. The signals HL and LL output by the switching power supply module are overcurrent detection signals, which are input to the level shift circuit. The output signals of the level shift circuit are A and B, which are input to the two comparison signal input ports of the overcurrent comparator. The overcurrent comparator outputs a signal E, and the signal E is input to the switching power supply for controlling the charging of the output terminal Vout, so that the output voltage rises slowly.

What is important in the design of the present invention is its topological structure and the compensation method realized by this topological structure. The topological structure mentioned in the present invention mainly consists of four modules. For circuit design engineers, the design and realization of each module is very easy, and there are many ways to realize it. In the compensation method of the present invention, the compensation voltage is generated by the charging timing and the compensation voltage generation circuit module, and one of the two input signals input to the overcurrent comparator module is compensated, so that the threshold for judging whether a current surge phenomenon occurs follows the start-up It increases slowly with the increase of charging time. Furthermore, the starting process of the switching power supply is kept as stable as possible, and the phenomenon of multiple restarts due to overcurrent does not occur.

These four modules of charging timing and compensation voltage generating circuit, level shifting circuit, overcurrent comparator and switching power supply of the present invention can have many kinds of circuit technology implementation schemes, as utilizing CMOS (complementary metal oxide semiconductor) technology, bipolar Type technology, BiCMOS (bipolar-complementary metal oxide semiconductor) technology, etc., can even be realized with different materials, such as GaAs (gallium arsenide) and SiGe (silicon germanium). Moreover, the present invention can be applied to switching power supplies with different structures, such as step-up switching power supplies, step-down switching power supplies, and the like. All of the above all belong to the extension and applicable scope of the present invention.

One embodiment of the present invention is a synchronous rectification step-down switching power supply soft start circuit, its specific structure is shown in Figure 2, by charging timing and compensation voltage generation circuit I, level shift circuit II, overcurrent comparison It is composed of four modules: device III and switching power supply IV. In this embodiment, the working voltage shared by the charging timing and compensation voltage generating circuit I, the level shifting circuit II, and the overcurrent comparator III is 5V; the input power of the switching power supply IV is 10V. The specific implementation circuits of each module are separated by dotted boxes, and their components are described in detail as follows:

The charging timing and compensation voltage generating circuit I of the present embodiment is composed of current source I4, transistor m14 and transistor mx, transistor T4 and transistor T6, resistor R5, compensation resistor R6, resistor R8, resistor R10 and resistor R11, capacitor C2, reverse phase Inverter inv1, inverter inv2 and inverter inv3; the connection relationship is: one end of the current source I4 is connected to the power supply 5V, and the other end is connected to the source of the transistor m14; the gate of the transistor m14 is connected to the inverter inv1 The output terminal of the transistor m14 is connected to one end of the resistor R5; the start signal EN1 of the module is connected to the input terminal of the inverter inv1; the collector of the transistor T4 is connected to the power supply 5V, and its emitter is connected to the resistor R11 One end of the resistor R5, the input end of the inverter inv2, the emitter of the transistor T6, the drain of the transistor mx and one end of the capacitor C2 at the same time; the collector of the transistor T6 is connected to the resistor R8 One end, its base is connected to one end of the resistor R10; the other end of the resistor R10 is connected to a 2.5V reference voltage, and the other end of the resistor R8 is grounded; the source of the transistor mx is connected to the ground, and its gate is connected to the inverter inv1 The output end of the capacitor C2; the other end of the capacitor C2 is grounded; one end of the compensation resistor R6 is grounded, the other end is connected to the other end of the resistor R11, and the output compensation voltage Vc is sent to the level shift circuit module; the output of the inverter inv2 is connected to the inverter The input terminal of inv3 is connected to the enable signal EN2; the output terminal of the inverter inv3 is connected to the soft start failure indication signal F.

Level shift circuit II is a symmetrical structure, including transistor t1, transistor t2 and transistor T3, transistor m1, transistor m2, transistor m3, transistor m4, transistor m5, transistor m9, transistor m10 and transistor m11, resistor R1, resistor R2 , resistor R3, resistor R4, resistor R9 and current source I3; its connection relationship is: the collector and base of transistor T3 are connected to the power supply 5V, and its emitter is connected to the source of transistor m3, transistor m4 and transistor m5; m3, transistor m4, and transistor m5 are in common gate, and the drain of transistor m5 is connected with its own gate together, and connected to the drain of transistor m9; the drain of transistor m3 is connected to one end of resistor R4 and transistor t1 Emitter; the drain of transistor m4 is connected to one end of resistor R3 and the emitter of transistor t2; the other end of resistor R3 is connected to one end of resistor R1 and the output signal A; the other end of resistor R4 is connected to one end of resistor R2 and On the output signal B; the other end of the resistor R1 is connected to the drain of the transistor m1 and the signal HL of the switching power supply module; the other end of the resistor R2 is connected to the drain of the transistor m2 and the output signal LL of the switching power supply module; the transistor m1 , the transistor m2, the transistor m9, the transistor m10 and the transistor m11 have a common gate, and are connected to the start signal EN1; the source of the transistor m1 and the drain of the transistor m11 are connected together, and are connected to the base of the transistor t2, and the transistor m2 The source is connected to the drain of the transistor m10, and is connected to the base of the transistor t1; the source of the transistor m11 is connected to one end of the resistor R9, and the other end of the resistor R9 is grounded; the source of the transistor m10 is connected to the compensation voltage Vc; the transistor The source of m9 is connected to one end of the current source I3, and the other end of the current source I3 is grounded; the collectors of the transistor t1 and the transistor t2 are all grounded.

The over-current comparator uses a high-precision voltage comparator comp. The reason why it is called an over-current comparator is that the signal voltage input to the voltage comparator is a sampling of the current value. When the over-current phenomenon occurs, the output of the comparator occurs Inversion; a typical embodiment thereof is shown in Figure 3. The circuit module is composed of current source I1, transistors M1, M2, M3, M4, M5, M6, M7, M8 and M9, inverters inv1', inv2' and inv3', and its connection relationship is: transistor M1 and transistor M2 has a common gate, and the gate of transistor M1 is connected to its own drain; the sources of transistor M1, transistor M2, and transistor M3 are all connected to the power supply voltage vdd; the drain of transistor M1 is also connected to the drain of transistor M4 pole; the drain of transistor M2 is connected to the drain of transistor M5, and is connected to the gate of transistor M8 at the same time; the gates of transistor M4 and transistor M5 are respectively connected to the positive and negative input terminals of the comparator; the sources of transistor M4 and transistor M5 The pole is connected to the drain of transistor M6 at the same time; the source of transistor M6 is grounded; the common gate of transistor M6 and transistor M7; the source of transistor M7 is also grounded, and its gate and drain are connected together; the drain of transistor M7 and The drains of the transistor M9 are connected together; the source of the transistor M9 is connected together with one end of the current source I1; the other end of the current source I1 is connected to the power supply voltage vdd; the gate of the transistor M9 is connected to the output of the inverter inv1 terminal; the input of the inverter inv1 is connected to the input signal (EN); the gate of the transistor M3 is connected to its own drain; the drain of the transistor M3 is connected to the drain of the transistor M8 at the same time; the drain of the transistor M8 The source is grounded; the drain of the transistor M8 is connected to the input terminal of the inverter inv2; the output terminal of the inverter inv2 is connected to the input terminal of the inverter inv3; the output terminal of the inverter inv3 is connected to the output signal E.

The step-down switching power supply IV of the synchronous rectification structure of the present embodiment includes a transistor M2x, a transistor M2x1, an inductor L1, a resistor R14 and a capacitor C1; the connection relationship is: the drain of the transistor M2x is connected to the input voltage Vin, and the drain of the transistor M2x The gate is connected to the output signal E of the overcurrent comparator, the source of the transistor M2x is connected to the drain of the transistor M2x1, and connected to one end of the inductor L1; the gate of the transistor M2x1 is connected to the soft start failure indication signal F, The source of the transistor M2x1 is grounded; the other end of the inductor L1 is connected to one end of the resistor R14, and at the same time connected to the output signal HL of the switching power supply module; the other end of the resistor R14 is connected to one end of the output capacitor C1, and simultaneously connected to the switching power supply module The output signal LL and the output signal V; the other end of the capacitor C1 is grounded. The connection relationship of the overall circuit of this embodiment is shown in Figure 2: first, the sampling signals HL and LL are drawn from both ends of the resistor R14 in the step-down switching power supply module of the synchronous rectification structure, and the voltage difference between the signals HL and LL is The size reflects the size of the current flowing through the resistor R14, that is, the size of the current flowing through the inductor. The output signals HL and LL are connected to respective inputs HL and LL of the level shifting circuit. The compensation voltage Vc generated by the charging timing and compensation voltage generating circuit is connected to the level shifting circuit through the resistor R6 of the level shifting circuit to compensate the LL terminal of the current sampling signal HL and LL signal pair. The output signal of the level shift circuit is connected to the inverting and non-inverting input terminals of the overcurrent comparator comp through nodes A and B, and the output E of the overcurrent comparator comp is connected to the gate input terminal of M2x to control the conduction and cut off, thereby controlling the peak value of the current flowing through the resistor R14. After the charging timing and compensation voltage generating circuit is input enabling signal EN1 is valid, the whole circuit enters the soft start state.

Its working process is as follows: as shown in Figure 2. First, the EN1 signal is low level, and the voltage across C2 is initialized to OV through mx; after that, the EN1 signal is high level. At this time, on the one hand, m14 is turned on, and the current source I4 starts to charge the capacitor C2 through m14. Before the voltage of C2 is charged to 2.5V, the output EN2 of inv2 is always at a high level (because the inversion threshold of inv2 is 2.5V V, and T6, R10 and R8 can ensure that the voltage of C2 can be charged above 2.5V), the high-level enabled overcurrent comparator comp starts to work (under normal circumstances, the comparator output E is high, and the control switch The power supply module charges the output Vout); on the other hand, m1, m2, m10 and m11 are also turned on, and the level shift circuit starts to work. During this process, two detection signals HL and LL are fed back to the level shift circuit from both ends of the sensitive resistor R14 that detects the inductor current, (the voltage difference between HL and LL reflects the level of the inductor current, by limiting The magnitude of the voltage difference can limit the occurrence of current surge phenomenon.) The overcurrent comparator is to judge the magnitude of the voltage difference between the two ends of HL and LL. If the difference is large, the node E is low, otherwise Node E is high. Node E controls the high-end tube M2x of the synchronous rectifier (the switch tube close to the power input terminal). If the inductor current is over-current, the voltage difference across the sensitive resistor R14 increases, so that the node E is at a low level, the high-side switch is turned off, and the inductor over-current phenomenon is controlled. In this way, the feedback signal provided by the sensitive resistor R14, coupled with the control of the over-current comparator comp, can make the inductor current rise slowly without over-current.

With the increase of time, the current of the inductor increases to a certain level, which will make the voltage difference across the sensitive resistor R14 maintain a high value for a certain period of time, so that the node E remains at a high level for a long time, slowing down The speed of the soft start. For this reason, a compensation voltage V _c is introduced to one end of the level shift circuit (LL feedback input end), so that the voltage difference input to the two ends of the overcurrent comparator can be maintained at a relatively stable level. The continuous slow increase of the inductor current and the linear increase of the output voltage are guaranteed. Voltage compensation is provided through R6, because the current of resistor R6 includes two parts: one is the same current provided by the level shift circuit as R9, and the other is the current flowing through the emitter of T4, which is due to the voltage on capacitor C2 (The increase of C2 voltage is due to the charging of constant current source I4). Then the voltage on R6 increases slowly. It can be seen from Figure 2 that the maximum compensation voltage of V _c is 2.5V*R6/(R11+R6).

If the voltage across the capacitor C2 exceeds 2.5V, but the output voltage of the switching power supply still does not reach the value set by the system, it is considered that the soft start has failed. At this time, the output EN2 of the inverter inv2 is at a low level, so that the high-side switch tube M2x in the step-down switching power supply module with a synchronous rectification structure is turned off, the low-side switch tube M2x1 is turned on, the output voltage is discharged to the ground, and the system restarts. start up. In order to prevent the restart of the switching power supply, the values of C2 and I4 must be designed in the circuit design, so that before the voltage of the capacitor C2 reaches 2.5V, the voltage of the capacitor C1 at the output terminal of the switching power supply should have reached the threshold value of the system design in advance . When the system detects that the output voltage of the switching power supply reaches the threshold, the system outputs a signal to EN1 to stop the soft-start circuit and start the control core of the switching power supply at the same time, which is generally realized by a finite state machine (not belonging to the scope of this embodiment) , the finite state machine replaces the soft-start circuit to keep the output voltage stable.

Using the soft-start circuit of this embodiment in a specific output voltage of 3.3V step-down switching power supply system, the HSPICE simulation shows that if the soft-start circuit is not used, and the capacitor at the output end of the switching power supply is directly charged, the simulated The results are shown in Figure 4, where (a) is the change curve of the inductor current with time, and (b) is the change curve of the output voltage of the switching power supply with time. It can be seen that a surge current (current overshoot) is generated, and the current can reach nearly 10A, which may cause damage to the electronic system. If the soft-start circuit of this embodiment is used, the result is shown in FIG. 5 , where (a) is the variation curve of the inductor current with time, and (b) is the variation curve of the output voltage of the switching power supply with time. It can be seen that the inductor current rises slowly, and the voltage at the output end of the switching power supply also rises gradually, which meets the design goal.

Claims (4)

1. A DC/DC switching power supply soft start circuit using voltage compensation, characterized in that it is composed of four modules: charging timing and compensation voltage generating circuit, level shift circuit, overcurrent comparator and switching power supply; its connection relationship The starting signal EN1 is connected to the input port of the charging timing and compensation voltage generating circuit, the compensation voltage Vc output port of the charging timing and compensation voltage generating circuit is connected to the input terminal of the level shift circuit, and the charging timing and compensation voltage generation The soft-start failure indication signal F output port of the circuit is connected to the input terminal of the switching power supply module, and the enable signal EN2 output port of the charging timing and compensation voltage generating circuit is connected to the input terminal of the overcurrent comparator; the output signal of the switching power supply module The ports of HL and LL are connected with the input terminals of the level shift circuit; the ports of the output signals A and B of the level shift circuit are connected with the two comparison signal input ports of the overcurrent comparator; the output signal of the overcurrent comparator The port of E is connected to the input terminal of the switching power supply; the charging timing and compensation voltage generation circuit, the level shift circuit and the overcurrent comparator module share the working voltage Vin1, and the input power supply voltage of the switching power supply module is Vin2; Said charging timing and compensating voltage generating circuit are composed of current source I4, transistor m14 and transistor mx, transistor T4 and transistor T6, resistor R5, compensating resistor R6, resistor R8, resistor R10 and resistor R11, capacitor C2, inverter inv1 , composed of inverter inv2 and inverter inv3; its connection relationship is: one end of current source I4 is connected to the power supply 5V, and the other end is connected to the source of transistor m14; the gate of transistor m14 is connected to the output of inverter inv1 terminal, and the drain of transistor m14 is connected to one end of resistor R5; the start signal EN1 of this module is connected to the input terminal of inverter inv1; the collector of transistor T4 is connected to power supply 5V, and its emitter is connected to one end of resistor R11 , and its base is simultaneously connected to one end of the resistor R5, the input end of the inverter inv2, the emitter of the transistor T6, the drain of the transistor mx and one end of the capacitor C2; the collector of the transistor T6 is connected to one end of the resistor R8, Its base is connected to one end of the resistor R10; the other end of the resistor R10 is connected to a 2.5V reference voltage, and the other end of the resistor R8 is grounded; the source of the transistor mx is grounded, and its gate is connected to the output of the inverter inv1 end; the other end of the capacitor C2 is grounded; one end of the compensation resistor R6 is grounded, and the other end is connected to the other end of the resistor R11, and the output compensation voltage Vc is sent to the level shift circuit module; the output of the inverter inv2 is connected to the inverter inv3 The input terminal of the inverter and the enable signal EN2; the output terminal of the inverter inv3 is connected to the soft start failure indication signal F. 2. The DC/DC switching power supply soft start circuit using voltage compensation as claimed in claim 1, characterized in that said level shift circuit includes transistor t1, transistor t2 and transistor T3, transistor m1, transistor m2, transistor m3, transistor m4, transistor m5, transistor m9, transistor m10 and transistor m11, resistor R1, resistor R2, resistor R3, resistor R4 and resistor R9, and current source I3; the connection relationship is: the collector and base of transistor T3 are connected In the power supply 5V, its emitter is connected to the source of transistor m3, transistor m4 and transistor m5; To the drain of transistor m9; the drain of transistor m3 is connected to one end of resistor R4 and the emitter of transistor t1; the drain of transistor m4 is connected to one end of resistor R3 and the emitter of transistor t2; the other end of resistor R3 is connected to One end of the resistor R1 is connected to the output signal A; the other end of the resistor R4 is connected to one end of the resistor R2 and the output signal B; the other end of the resistor R1 is connected to the drain of the transistor m1 and the output signal HL of the switching power supply module; the resistor The other end of R2 is connected to the drain of the transistor m2 and the output signal LL of the switching power supply module; the transistor m1, the transistor m2, the transistor m9, the transistor m10 and the transistor m11 are connected to the start signal EN1; the source of the transistor m1 The drain of the transistor m11 is connected together and connected to the base of the transistor t2, the source of the transistor m2 is connected to the drain of the transistor m10, and connected to the base of the transistor t1; the source of the transistor m11 is connected to the resistor R9 One end of the resistor R9, the other end of the resistor R9 is grounded; the source of the transistor m10 is connected to the compensation voltage Vc; the source of the transistor m9 is connected to one end of the current source I3, and the other end of the current source I3 is grounded; the set of the transistor t1 and the transistor t2 The electrodes are all grounded. 3. The DC/DC switching power supply soft start circuit adopting voltage compensation as claimed in claim 1, wherein said overcurrent comparator is composed of current source I1, transistors M1, M2, M3, M4, M5, M6 , M7, M8 and M9, composed of inverters inv1', inv2' and inv3', the connection relationship is: the transistor M1 and the transistor M2 have a common gate, and the gate of the transistor M1 is connected to its own drain; the transistor The sources of M1, transistor M2, and transistor M3 are all connected to the power supply voltage vdd; the drain of transistor M1 is also connected to the drain of transistor M4; the drain of transistor M2 is connected to the drain of transistor M5, and at the same time connected to the drain of transistor M8 The gate of the transistor M4 and the gate of the transistor M5 are respectively connected to the positive and negative input terminals of the comparator; the sources of the transistor M4 and the transistor M5 are connected to the drain of the transistor M6 at the same time; the source of the transistor M6 is grounded; the transistor M6 and The common gate of the transistor M7; the source of the transistor M7 is also grounded, and its gate and drain are connected together; the drain of the transistor M7 and the drain of the transistor M9 are connected together; the source of the transistor M9 is connected to one end of the current source I1 connected together; the other end of the current source I1 is connected to the power supply voltage vdd; the gate of the transistor M9 is connected to the output of the inverter inv1; the input of the inverter inv1 is connected to the input signal EN; the gate of the transistor M3 The drain of the transistor M3 is connected to the drain of the transistor M8 at the same time; the source of the transistor M8 is grounded; the drain of the transistor M8 is connected to the input of the inverter inv2; the inverter The output terminal of inv2 is connected to the input terminal of the inverter inv3; the output terminal of the inverter inv3 is connected to the output signal E. 4. The DC/DC switching power supply soft-start circuit using voltage compensation as claimed in claim 1, characterized in that said switching power supply includes transistor M2x, transistor M2x1, inductor L1, resistor R14 and capacitor C1; its connection relationship Yes: the drain of the transistor M2x is connected to the input voltage Vin, the gate of the transistor M2x is connected to the output signal E of the overcurrent comparator, the source of the transistor M2x is connected to the drain of the transistor M2x1, and connected to the inductor L1 One end; the gate of the transistor M2x1 is connected to the soft start failure indication signal F, and the source of the transistor M2x1 is grounded; the other end of the inductor L1 is connected to one end of the resistor R14, and at the same time connected to the output signal HL of the switching power supply module; the resistor R14 The other end of the capacitor C1 is connected to one end of the output capacitor C1, and is simultaneously connected to the output signal LL and the output signal V of the switching power supply module; the other end of the capacitor C1 is grounded.

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