A soft start circuit, a driving circuit and a switching power supply

Abstract

The present invention relates to the field of DC-DC converters, and discloses a soft start circuit, a drive circuit, and a switching power supply. The soft start module and the soft start module generate a fast start voltage and a slow start voltage respectively, and the voltages are sent to the soft start judgment module to judge the current soft start state, and the output soft start judgment signal is sent to the error amplifier to control the internal circuit. The minimum voltage selection circuit outputs the smaller of the slow start voltage and the reference voltage, and sends it to the positive input terminal of the error amplifier. The negative input terminal of the error amplifier is connected to the feedback voltage, and the two negative and positive input terminals are connected to the fast start voltage and the output of the minimum voltage selection circuit, so that the feedback voltage follows the start voltage rise and finally follows the reference voltage, and the risk of current surge is greatly reduced. The present invention reduces the risk of current surge by additionally introducing a fast start voltage and related control circuits, thereby improving the reliability of the system.

Description

Technical Field

[0001] The invention relates to the field of DC-DC converters, and in particular to a soft start circuit, a drive circuit and a switching power supply. Background Art

[0002] During the startup process of the DC-DC converter, the reference voltage is established first, which causes the output voltage to rise rapidly and generate a large current surge, thereby generating a large amount of heat, causing the chip to overheat or even fail. Therefore, a reasonable soft-start control solution is needed to make the output voltage rise slowly and reduce the current surge.

[0003] Today's soft start method usually charges a large capacitor with a small current to generate a slowly rising ramp voltage, which is then sent to the input of the error amplifier, so that the feedback voltage slowly rises with the soft start voltage. However, when a system failure occurs, the system will re-execute the power-on soft start, which will take a lot of time. Summary of the invention

[0004] In view of this, the present invention provides a soft start circuit, a drive circuit and a switching power supply to solve the problem of how to reduce current surge during the soft start process and how to quickly restore power after a system failure.

[0005] In the first aspect, the present invention provides a soft start circuit, including: a fast soft start module, a slow soft start module, a soft start judgment module, a minimum voltage selection circuit, and an error amplification circuit, wherein the output end of the fast soft start module is connected to the first input end of the soft start judgment module, and the fast soft start module is used to output a fast start voltage; the output end of the slow soft start module is connected to the second input end of the soft start judgment module and the first input end of the minimum voltage selection circuit, and the slow soft start module is used to output a slow start voltage; the rising slope of the fast start voltage is greater than the rising slope of the slow start voltage; the third input end and the fourth input end of the soft start judgment module are respectively input with a high threshold voltage and a low threshold voltage, and the output end of the soft start judgment module is connected to the control end of the error amplification circuit; the soft start judgment module is used to generate a soft start end judgment signal according to the fast start voltage and the slow start voltage, and the soft start end judgment signal is used to control the start and stop of the error amplification circuit; the second input end of the minimum voltage selection circuit is input with a reference voltage, the output end of the minimum voltage selection circuit is connected to the first positive input end of the error amplifier circuit, and the minimum voltage selection circuit is used to output the smaller of the slow start voltage and the divided voltage of the reference voltage; the second positive input end of the error amplifier circuit is connected to the output end of the fast soft start module, the negative input end of the error amplifier circuit inputs the feedback voltage, the output end of the error amplifier circuit is connected to the input end of the peripheral PWM module, the PWM module generates a switching signal based on the output voltage of the error amplifier circuit, and the switching signal is used to control the on-off state of the electronic switch in the switching power supply; the feedback voltage is the output voltage of the switching power supply; after the system is powered on, the fast start voltage controls the soft start of the error amplifier circuit; before the soft start is completed and after the error amplifier circuit has completed the soft start, the error amplifier circuit controls the feedback voltage to follow the smaller of the fast start voltage and the output voltage of the minimum voltage selection circuit; after the system fails and is relieved, the error amplifier circuit controls the feedback voltage to follow the fast start voltage to recover quickly.

[0006] The soft start module and the soft start module of the present invention respectively generate a fast start voltage and a slow start voltage, and the voltages are sent to the soft start discrimination module to judge the current soft start state, and the output soft start discrimination signal is sent to the error amplifier to control the internal circuit. The minimum voltage selection circuit outputs the smaller of the slow start voltage and the reference voltage, and sends it to the positive input terminal of the error amplifier. The negative input terminal of the error amplifier is connected to the feedback voltage, and the two negative and positive input terminals are connected to the fast start voltage and the output of the minimum voltage selection circuit, so that the feedback voltage follows the start voltage rise and finally follows the reference voltage, and the risk of current surge is greatly reduced. The present invention reduces the risk of current surge by additionally introducing a fast start voltage and a related control circuit, thereby improving the reliability of the system.

[0007] In an optional embodiment, the fast soft start module includes: a first current source, a first starting capacitor, and a first transistor, wherein the input end of the first current source inputs a supply voltage, the output end of the first current source is connected to the first end of the first starting capacitor and the first end of the first transistor; the second end of the first transistor is connected to the second end of the first starting capacitor, the second end of the first transistor is also grounded, and the control end of the first transistor inputs a control command; the first end of the first starting capacitor is connected to the first input end of the soft start judgment module and the second positive input end of the error amplifier circuit; when the system fails or is not powered on, the control command lowers the fast start voltage; when the system is not faulty and is powered on, the control command raises the fast start voltage.

[0008] In an optional embodiment, the slow soft start module includes: a second current source, a second starting capacitor, and a second transistor, wherein the input end of the second current source inputs the supply voltage, the output end of the second current source is connected to the first end of the second starting capacitor and the first end of the second transistor; the second end of the second transistor is connected to the second end of the second starting capacitor, the second end of the second transistor is also grounded, and the control end of the second transistor inputs the control command; the first end of the second starting capacitor is connected to the second input end of the soft start judgment module and the first input end of the minimum voltage selection circuit; when the system is not powered on, the control command lowers the fast start voltage; when the system is powered on, the control command raises the fast start voltage.

[0009] In an optional embodiment, the soft start judgment module circuit includes: a selector, a first comparator, a first NOT gate and a second NOT gate, wherein a high threshold voltage is input to the first input end of the selector, and a low threshold voltage is input to the second input end of the selector; a fast start voltage is input to the first positive input end of the first comparator, and a slow start voltage is input to the second positive input end of the first comparator, the negative input end of the first comparator is connected to the output end of the selector, and the output end of the first comparator is connected to the input end of the first NOT gate; the output end of the first NOT gate is connected to the input end of the second NOT gate and the control end of the selector, and the output end of the second NOT gate is connected to the control end of the error amplifier circuit; when the soft start is not completed and the system is not faulty, the selector outputs a high threshold voltage, and the soft start end judgment signal is a low level; when the fast start voltage and the slow start voltage are higher than the high threshold voltage, the first comparator outputs a high level, the soft start end judgment signal is a high level, and the selector outputs a low threshold voltage; when the system fails, the first comparator outputs a low level, the soft start end judgment signal is a low level, and the selector outputs a high threshold voltage.

[0010] In an optional embodiment, the minimum voltage selection circuit includes: a second comparator, a third transistor, a fourth transistor, a first resistor, a second resistor, a third resistor, and a first capacitor, wherein the negative input terminal of the second comparator inputs a slow start voltage; the first end of the third transistor is connected to the first end of the first resistor, the second end of the fourth transistor, the first end of the second resistor, and the second end of the third resistor, the second end of the third transistor is connected to the second end of the second resistor, the second end of the third transistor is also grounded, the control end of the third transistor is connected to the second end of the first resistor through the first capacitor, and the control end of the third transistor is also connected to the output end of the second comparator; the first end of the fourth transistor inputs a power supply voltage, and the control end of the fourth transistor inputs a control voltage; the first end of the third resistor inputs a reference voltage, and the second end of the third resistor is connected to the positive input terminal of the second comparator; when the slow start voltage is less than the divided voltage of the reference voltage, the second transistor is turned on, and the first positive input terminal of the error amplifier circuit inputs the slow start voltage; when the slow start voltage is greater than the divided voltage of the reference voltage, the second transistor is turned on, and the first positive input terminal of the error amplifier circuit inputs the divided voltage of the reference voltage.

[0011] In an optional embodiment, the error amplifier circuit includes: a built-in soft start circuit and an EA core circuit, wherein the first control terminal of the built-in soft start circuit inputs a soft start end judgment signal, the second control terminal of the built-in soft start circuit inputs a slow start voltage, the third control terminal of the built-in soft start circuit inputs a soft start end judgment signal, the input terminal of the built-in soft start circuit inputs a power supply voltage, the first output terminal of the built-in soft start circuit is connected to the first control terminal of the EA core circuit, the second output terminal of the built-in soft start circuit is connected to the first input terminal of the EA core circuit, and the third output terminal of the built-in soft start circuit is grounded; the second control terminal of the EA core circuit inputs a control voltage, The third control terminal of the EA core circuit inputs a feedback voltage, the fourth control terminal of the EA core circuit inputs a fast start voltage, the fifth control terminal of the EA core circuit is connected to the output terminal of the fast soft start module, the second input terminal of the EA core circuit inputs a power supply voltage, the first output terminal of the EA core circuit is connected to the PWM module, and the second output terminal of the EA core circuit is grounded; when the soft start end judgment signal is a low level, the soft start end judgment signal controls the built-in soft start circuit to turn on, and the built-in soft start circuit injects a negative offset voltage into the first input terminal of the EA core circuit; when the soft start end judgment signal is a high level, the soft start end judgment signal controls the built-in soft start circuit to turn off.

[0012] In an optional embodiment, the built-in soft start circuit includes: a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a third current source, a first controllable switch and a second controllable switch, wherein the first end of the fifth transistor inputs a power supply voltage, the second end of the fifth transistor is connected to the first end of the third current source and the first end of the sixth transistor, and the control end of the fifth transistor is connected to the second end thereof, the control end of the sixth transistor and the first control end of the EA core circuit; the second end of the sixth transistor is connected to the first end of the seventh transistor and the first end of the eighth transistor respectively through the first controllable switch; the second end of the seventh transistor is connected to the first end thereof and the second end of the third current source, and the second end of the seventh transistor is also grounded; the second end of the eighth transistor is connected to the first input end of the EA core circuit through the second controllable switch; the control end of the first controllable switch inputs a soft start end judgment signal; the control end of the second controllable switch inputs a slow start voltage; when the soft start end judgment signal is at a low level, the soft start end judgment signal controls the first controllable switch and the second controllable switch to be turned on; when the soft start end judgment signal is at a high level, the soft start end judgment signal controls the first controllable switch and the second controllable switch to be turned off.

[0013] In an optional embodiment, the EA core circuit includes: a ninth transistor, a tenth transistor, an eleventh transistor, a twelfth transistor, a thirteenth transistor, a fourteenth transistor, a fifteenth transistor, a sixteenth transistor, a seventeenth transistor, an eighteenth transistor, and a nineteenth transistor, wherein a first end of the ninth transistor inputs a power supply voltage, a second end of the ninth transistor is connected to a first end of the sixteenth transistor, and a control end of the ninth transistor is connected to a control end of the eleventh transistor; a first end of the tenth transistor inputs a power supply voltage, a second end of the tenth transistor is connected to a first end of the twelfth transistor, a first end of the thirteenth transistor, a first end of the fourteenth transistor, and a control end of the fifteenth transistor, and a control end of the tenth transistor is connected to a control end of the fifth transistor; a first end of the eleventh transistor inputs a power supply voltage, a second end of the eleventh transistor is connected to a first end of the nineteenth transistor and a PWM module; a second end of the twelfth transistor is connected to a first end of the seventeenth transistor, and a control end of the twelfth transistor inputs a control voltage voltage; the twelfth transistor is always in the cut-off state; the second end of the thirteenth transistor is connected to the first end of the seventeenth transistor, and the control end of the thirteenth transistor inputs the feedback voltage; the second end of the fourteenth transistor is connected to the first end of the eighteenth transistor, and the second end of the fourteenth transistor is also connected to the second end of the eighth transistor through the second controllable switch, and the control end of the fourteenth transistor inputs the fast start voltage; the size of the thirteenth transistor is larger than the size of the fourteenth transistor; the second end of the fifteenth transistor is connected to the first end of the eighteenth transistor, and the control end of the fifteenth transistor is connected to the output end of the fast soft start module; the second end of the sixteenth transistor is connected to the second end of the seventeenth transistor, and the second end of the sixteenth transistor is also grounded, and the control end of the sixteenth transistor is connected to the first end of the seventeenth transistor and the control end of the seventeenth transistor; the second end of the eighteenth transistor is connected to the second end of the nineteenth transistor, and the second end of the eighteenth transistor is also grounded, and the control end of the eighteenth transistor is connected to its first end and the control end of the nineteenth transistor.

[0014] In a second aspect, the present invention provides a driving circuit, comprising: a soft start circuit and a PWM module according to the first aspect and any optional implementation manner thereof, wherein the output end of the soft start circuit is connected to the input end of the PWM module; the output end of the PWM module is connected to an electronic switch in a switching power supply; the PWM module generates a switching signal based on the output voltage of the error amplifier circuit, and the switching signal is used to soft start the electronic switch in the switching power supply and control the on-off state of the electronic switch.

[0015] In a second aspect, the present invention provides a switching power supply, comprising: a driving circuit of the second aspect and a switching power supply body, wherein the output end of the soft start circuit is connected to the input end of the PWM module; the output end of the PWM module is connected to an electronic switch in the switching power supply body; the PWM module generates a switching signal based on the output voltage of the error amplifier circuit, and the switching signal is used to soft-start the electronic switch in the switching power supply body and control the on-off state of the electronic switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 is a composition diagram of a soft start circuit according to an embodiment of the present invention;

[0018] Figure 2 is a schematic diagram of a soft start process according to an embodiment of the present invention;

[0019] Figure 3 is a specific circuit structure diagram of a fast start module and a slow start module according to an embodiment of the present invention;

[0020] Figure 4 is a specific circuit structure diagram of a soft start discrimination circuit according to an embodiment of the present invention;

[0021] Figure 5 is a specific circuit structure diagram of a minimum voltage selection circuit according to an embodiment of the present invention;

[0022] Figure 6 is a specific circuit structure diagram of an error amplifier circuit according to an embodiment of the present invention;

[0023] Figure 7 is a diagram showing the soft-start effect of a switching power supply after adopting the soft-start circuit according to an embodiment of the present invention;

[0024] Figure 8 4 is a diagram showing the composition of a driving circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0026] In this embodiment, a soft start circuit is provided. Figure 1 As shown, it includes: a fast soft start module 1, a slow soft start module 2, a soft start determination module 3, a minimum voltage selection circuit 4, and an error amplification circuit 5.

[0027] like Figure 1 As shown, the output end of the fast soft start module 1 is connected to the first input end of the soft start determination module 3, and the fast soft start module 1 is used to output a fast start voltage (i.e., SS1); the output end of the slow soft start module 2 is connected to the second input end of the soft start determination module 3 and the first input end of the minimum voltage selection circuit 4, and the slow soft start module 2 is used to output a slow start voltage (i.e., SS2); the rising slope of the fast start voltage is greater than the rising slope of the slow start voltage.

[0028] Specifically, two soft start modules are provided, and the two soft start modules generate a fast soft start voltage and a slow soft start voltage respectively, wherein the fast soft start voltage is used to quickly restore power-on and soft start of the error amplifier after a system fault is removed, and the slow soft start voltage is used to control the soft start time when the system is powered on.

[0029] like Figure 1 As shown, the third input terminal and the fourth input terminal of the soft start determination module 3 are respectively input with a high threshold voltage (i.e., VH) and a low threshold voltage (i.e., VL), and the output terminal of the soft start determination module 3 is connected to the control terminal of the error amplifier circuit 5; the soft start determination module 3 is used to generate a soft start end determination signal (i.e., SS_Flag) according to the fast start voltage and the slow start voltage, and the soft start end determination signal is used to control the start and stop of the error amplifier circuit 5.

[0030] Specifically, the soft start determination module 3 generates a soft start end determination signal by comparing and determining the fast soft start voltage and the slow soft start voltage. The soft start end determination signal indicates whether the system has completed the soft start.

[0031] like Figure 1 As shown, the reference voltage (i.e., VREF) is input to the second input terminal of the minimum voltage selection circuit 4, and the output terminal of the minimum voltage selection circuit 4 is connected to the first positive input terminal of the error amplifier circuit 5. The minimum voltage selection circuit 4 is used to output the smaller of the slow start voltage and the divided voltage of the reference voltage.

[0032] like Figure 1 As shown, the second positive input terminal of the error amplifier circuit 5 is connected to the output terminal of the fast soft start module 1, the negative input terminal of the error amplifier circuit 5 inputs the feedback voltage (i.e., VFB), the output terminal of the error amplifier circuit 5 is connected to the input terminal of the external PWM module, and the PWM module generates a switching signal based on the output voltage of the error amplifier circuit 5, and the switching signal is used to control the on-off state of the electronic switch in the switching power supply; the feedback voltage is the output voltage of the switching power supply.

[0033] Figure 1 In the embodiment, after the system is powered on, the fast start voltage controls the soft start of the error amplifier circuit 5; before the soft start is completed and after the error amplifier circuit 5 has completed the soft start, the error amplifier circuit 5 controls the feedback voltage to follow the smaller of the fast start voltage and the output voltage of the minimum voltage selection circuit 4; after the system fails and is relieved, the error amplifier circuit 5 controls the feedback voltage to follow the fast start voltage for rapid recovery.

[0034] Specifically, the overall control timing waveform of the system is as follows: Figure 2 When the system is powered on, the fast soft start voltage (SS1) and the slow soft start voltage (SS2) begin to rise, and the voltage SS1 rises faster and quickly completes the soft start of the error amplifier circuit 5 at time T1.

[0035] Figure 2 In the embodiment, before time T2, the slow start voltage SS2 rises slowly, and its voltage is less than the reference voltage VREF. The output voltage of the minimum voltage generating circuit is equal to the voltage of SS2. Therefore, at this time, the positive input terminal of the error amplifier circuit 5 is SS2, and the negative input terminal is VFB, so that the feedback voltage VFB is controlled to rise slowly following SS2 to complete the power-on soft start.

[0036] Figure 2 In the figure, at the moment T2-T3, the voltage of SS2 is greater than the reference voltage. At this time, the output voltage of the minimum voltage generating circuit is equal to the reference voltage VREF, which is equivalent to the positive input terminal of the error amplifier circuit 5 being VREF and the negative input terminal being VFB. Thus, VFB is controlled to be equal to VREF, and the system works normally.

[0037] Figure 2 In the example, at time T3-T4, a fault such as undervoltage lockout occurs in the system, at which time the voltage SS1 will be pulled down, thereby pulling down the feedback voltage protection circuit. At time T4, the fault is removed, and at this time the voltage SS1 will be released to repeat the rapid rise of the 0-T1 stage. Since the SS1 voltage is smaller than the reference voltage VREF during the T4-T5 stage, the feedback voltage VFB will rise rapidly following the voltage SS1 under the action of the error amplifier circuit 5, so as to complete the rapid recovery after the fault is removed.

[0038] Figure 2 In the T5-T6 stage, the voltage SS1 exceeds the reference voltage, and the error amplifier circuit 5 will make the feedback voltage VFB follow the reference voltage to complete the final stage of startup and resume normal operation. This avoids the overshoot of the output voltage due to the rapid startup following the voltage SS1.

[0039] In some optional embodiments, such as Figure 3 As shown, the fast soft start module 1 includes: a first current source I ss1 , the first starting capacitor C ss1 , first transistor S1.

[0040] like Figure 3 As shown, the first current source I ss1 The input terminal inputs the supply voltage, the first current source I ss1 The output terminal is connected to the first startup capacitor C ss1 The first end of the first transistor S1 is connected to the first start capacitor C ss1 The second end of the first transistor S1 is connected to the ground, the second end of the first transistor S1 is also grounded, and the control end of the first transistor S1 inputs the control command (ie, EN_SS1); the first startup capacitor C ss1 The first end is connected to the first input end of the soft start determination module 3 and the second positive input end of the error amplifier circuit 5.

[0041] Specifically, when the system fails or is not powered on, the control command pulls down the fast start voltage; when the system does not fail and is powered on, the control command pulls up the fast start voltage.

[0042] In some optional embodiments, such as Figure 3 As shown, the slow soft start module 2 includes: a second current source I ss2 , the second starting capacitor C ss2 , the second transistor S2.

[0043] like Figure 3 As shown, the second current source I ss2 The input supply voltage is input to the input terminal, and the second current source I ss2 The output terminal and the second startup capacitor C ss2 The first end of the second transistor S2 is connected to the first end of the second transistor S2; the second end of the second transistor S2 is connected to the second startup capacitor C ss2 The second end of the second transistor S2 is connected to the ground, the second end of the second transistor S2 is also grounded, and the control end of the second transistor S2 inputs the control command (ie, EN); the second startup capacitor C ss2 The first end is connected to the second input end of the soft start determination module 3 and the first input end of the minimum voltage selection circuit 4.

[0044] Specifically, when the system is not powered on, the control command pulls down the fast start voltage; when the system is powered on, the control command pulls up the fast start voltage.

[0045] Specifically, Figure 3 As shown, both the slow soft start module 2 and the fast start module use a fixed current to charge the capacitor to generate a ramp voltage. When the system fails or is not enabled, the EN_SS1 signal indicates a high level to pull down the voltage SS1 through the switch S1. When the system is not enabled, the EN signal indicates a high level to pull down the voltage SS2 through the switch S2.

[0046] According to the characteristics of the capacitor, the SS1 voltage is as shown in formula (1), where t is the charging time.

[0047] (1)

[0048] Similarly, the SS2 voltage is as shown in formula (2):

[0049] (2)

[0050] In order to make the rising speed of voltage SS1 much faster than that of voltage SS2, the condition of equation (3) needs to be satisfied. Generally, the rising slope of voltage SS1 can be designed to be 1 / 10 or less of that of voltage SS2.

[0051] (3)

[0052] In some optional embodiments, such as Figure 4 As shown, the circuit of the soft start determination module 3 includes: a selector U1, a first comparator CMP1, a first NOT gate NOT1 and a second NOT gate NOT2.

[0053] like Figure 4 As shown, a high threshold voltage is input to the first input terminal of the selector U1, and a low threshold voltage is input to the second input terminal of the selector U1; a fast start voltage is input to the first positive input terminal of the first comparator CMP1, and a slow start voltage is input to the second positive input terminal of the first comparator CMP1, a negative input terminal of the first comparator CMP1 is connected to the output terminal of the selector U1, and the output terminal of the first comparator CMP1 is connected to the input terminal of the first NOT gate NOT1; the output terminal of the first NOT gate NOT1 is connected to the input terminal of the second NOT gate NOT2 and the control terminal of the selector U1, and the output terminal of the second NOT gate NOT2 is connected to the control terminal of the error amplifier circuit 5.

[0054] Specifically, when the soft start is not completed and the system is not faulty, the selector U1 outputs a high threshold voltage, and the soft start end judgment signal is a low level; when the fast start voltage and the slow start voltage are higher than the high threshold voltage, the first comparator CMP1 outputs a high level, the soft start end judgment signal is a high level, and the selector U1 outputs a low threshold voltage; when the system fails, the first comparator CMP1 outputs a low level, the soft start end judgment signal is a low level, and the selector U1 outputs a high threshold voltage.

[0055] Figure 4 In the embodiment, voltage SS1 and voltage SS2 are sent to the positive input terminal of the first comparator CMP1, the negative input terminal of the first comparator CMP1 is connected to the output of the selector U1, and reference voltages VH and VL are sent to the two input terminals of the selector U1, where VH is a high threshold voltage and VL is a low threshold voltage. The selector U1 selects the voltage sent to the negative input terminal of the comparator according to the soft start determination signal SS_Flag.

[0056] Specifically, when the circuit soft start has not been completed, the selector U1 output is VH, and SS_Flag is low. When the voltage SS1 and the voltage SS2 are both greater than VH, the comparator output flips, the soft start judgment signal SS_Flag becomes high, and the output of the selector U1 becomes VL. When an abnormal situation such as a system failure occurs, the SS1 or SS2 voltage is less than VL, and the comparator output flips to low, the SS_Flag signal becomes low, and the output of the selector U1 becomes VH.

[0057] In some optional embodiments, such as Figure 5 As shown, the minimum voltage selection circuit 4 includes: a second comparator Amp1, a third transistor M1, a fourth transistor M2, a first resistor R1, a second resistor R2, a third resistor R3, and a first capacitor C1.

[0058] like Figure 5 As shown, the negative input terminal of the second comparator Amp1 inputs the slow start voltage; the first end of the third transistor M1 is connected to the first end of the first resistor R1, the second end of the fourth transistor M2, the first end of the second resistor R2, and the second end of the third resistor R3, the second end of the third transistor M1 is connected to the second end of the second resistor R2, the second end of the third transistor M1 is also grounded, the control end of the third transistor M1 is connected to the second end of the first resistor R1 through the first capacitor C1, and the control end of the third transistor M1 is also connected to the output end of the second comparator Amp1; the first end of the fourth transistor M2 inputs the power supply voltage, and the control end of the fourth transistor M2 inputs the control voltage; the first end of the third resistor R3 inputs the reference voltage, and the second end of the third resistor R3 is connected to the positive input terminal of the second comparator Amp1.

[0059] Specifically, when the slow start voltage is less than the divided voltage of the reference voltage, the second transistor S2 is turned on, and the slow start voltage is input to the first positive input terminal of the error amplifier circuit 5; when the slow start voltage is greater than the divided voltage of the reference voltage, the second transistor S2 is turned on, and the divided voltage of the reference voltage is input to the first positive input terminal of the error amplifier circuit 5.

[0060] Figure 5 In the figure, the minimum voltage selection circuit 4 compares the slow soft start voltage SS2 with the reference voltage VREF through the voltage divider VREF_DIV of resistors R2 and R3, and then outputs the voltage SS_REF. When the SS2 voltage is less than VREF_DIV, the gate voltage of M1 is high, M1 is turned on, the feedback loop is established, and the error amplifier circuit 5 pulls the SS_REF voltage to a voltage equal to SS2. The capacitor C1 and the resistor R1 (Miller resistor) are connected in series to ensure the stability of the loop. As the SS2 voltage increases, when the voltage exceeds VREF_DIV, the gate of M1 becomes low, the error amplifier circuit 5 cannot work normally, and the voltage of SS_REF is determined by VREF_DIV. As the SS2 voltage increases, the voltage of SS_REF will be maintained at the size of VREF_DIV.

[0061] In some optional embodiments, such as Figure 6 As shown, the error amplifier circuit 5 includes: a built-in soft start circuit 51 and an EA core circuit 52 .

[0062] like Figure 6 As shown, the first control terminal of the built-in soft start circuit 51 inputs the soft start end judgment signal, and the second control terminal (ie, M p7 The third control terminal of the built-in soft start circuit 51 (i.e., the control terminal of S1 and S2) inputs a soft start end judgment signal, the input terminal of the built-in soft start circuit 51 inputs a power supply voltage (i.e., VCC), and the first output terminal of the built-in soft start circuit 51 (i.e., the control terminal of M2) is connected to the first control terminal of the EA core circuit 52 (i.e., M p4 The second output terminal (ie, S2) of the built-in soft start circuit 51 is connected to the first input terminal (ie, M of the EA core circuit 52) p11 ) is connected, and the third output terminal of the built-in soft start circuit 51 is grounded.

[0063] like Figure 6 As shown, the second control terminal of the EA core circuit 52 inputs the control voltage (ie, VDD), the third control terminal of the EA core circuit 52 inputs the feedback voltage (ie, VFB), the fourth control terminal of the EA core circuit 52 inputs the fast start voltage (ie, SS1), and the fifth control terminal of the EA core circuit 52 (ie, M p11) is connected to the output end of the fast soft start module 1, the second input end of the EA core circuit 52 inputs the supply voltage (ie, VCC), and the first output end of the EA core circuit 52 (ie, M p5 ) is connected to the PWM module, and the second output terminal of the EA core circuit 52 is grounded.

[0064] Specifically, when the soft start end judgment signal is at a low level, the soft start end judgment signal controls the built-in soft start circuit 51 to turn on, and the built-in soft start circuit 51 injects a negative offset voltage into the first input terminal of the EA core circuit 52; when the soft start end judgment signal is at a high level, the soft start end judgment signal controls the built-in soft start circuit 51 to turn off.

[0065] In some optional embodiments, such as Figure 6 As shown, the built-in soft start circuit 51 includes: a fifth transistor M3, a sixth transistor M p2 , the seventh transistor M p6 , the eighth transistor M p7 , the third current source I bias , a first controllable switch S1 and a second controllable switch S2.

[0066] like Figure 6 As shown, the first end of the fifth transistor M3 inputs the supply voltage, and the second end of the fifth transistor M3 is connected to the third current source I bias The first end of the sixth transistor M p2 The first end of the fifth transistor M3 is connected to the second end of the sixth transistor M p2 The sixth transistor M is connected to the control end of the EA core circuit 52; p2 The second end of the transistor M is connected to the seventh transistor M through the first controllable switch S1. p6 The first end of the eighth transistor M p7 The first end of the seventh transistor M is connected; p6 The second end of the third current source I bias The second end of the seventh transistor M is connected p6 The second end of the eighth transistor M is also grounded; p7 The second end of is connected to the first input end of the EA core circuit 52 through the second controllable switch S2; the control end of the first controllable switch S1 inputs the soft start end judgment signal; the control end of the second controllable switch S2 inputs the slow start voltage.

[0067] Specifically, when the soft start end determination signal is at a low level, the soft start end determination signal controls the first controllable switch S1 and the second controllable switch S2 to turn on; when the soft start end determination signal is at a high level, the soft start end determination signal controls the first controllable switch S1 and the second controllable switch S2 to turn off.

[0068] In some optional embodiments, such as Figure 6 As shown, the EA core circuit 52 includes: a ninth transistor M p3 , the tenth transistor M p4 , the eleventh transistor M p5 , the twelfth transistor M p8 , the thirteenth transistor M p9 , the fourteenth transistor M p10 , the fifteenth transistor M p11 , the sixteenth transistor M N1 , the seventeenth transistor M N2 , the eighteenth transistor M N3 , the nineteenth transistor M N4 .

[0069] like Figure 6 As shown, the ninth transistor M p3 The first end of the ninth transistor M is input with a supply voltage. p3 The second end of the sixteenth transistor M N1 The first end of the ninth transistor M is connected p3 The control terminal of the eleventh transistor M p5 The tenth transistor M p4 The first end of the tenth transistor M is input with a supply voltage. p4 The second end of the twelfth transistor M p8 The first end of the thirteenth transistor M p9 The first end of the fourteenth transistor M p10 The first end of the fifteenth transistor M p11 The control terminal of the tenth transistor M is connected p4 The control end of the eleventh transistor M is connected to the control end of the fifth transistor M3; p5 The first end of the eleventh transistor M is input with a supply voltage. p5 The second end of the nineteenth transistor M N4 The first end of the PWM module is connected; the twelfth transistor M p8 The second terminal of the seventeenth transistor M N2 The first end of the twelfth transistor M p8 The control terminal of the twelfth transistor M is input with a control voltage; p8 The thirteenth transistor M is always in the cut-off state; p9 The second terminal of the seventeenth transistor M N2 The first end of the 13th transistor M is connected to the control end of the 14th transistor M; the feedback voltage is input to the control end of the 14th transistor M; p10 The second end of the eighteenth transistor M N3 The first end of the fourteenth transistor M is connected p10The second end of p7 is also connected to the second end of the eighth transistor M p10 . The control end of the fourteenth transistor M p9 inputs a fast start voltage; the size of the thirteenth transistor M p10 is larger than that of the fourteenth transistor M p11 . The second end of the fifteenth transistor M N3 is connected to the first end of the eighteenth transistor M p11 . The control end of the fifteenth transistor M N1 is connected to the output end of the fast soft start module 1; the second end of the sixteenth transistor M N2 is connected to the second end of the seventeenth transistor M N1 . The second end of the sixteenth transistor M N1 is also grounded. The control end of the sixteenth transistor M N2 is connected to the first end of the seventeenth transistor M N2 and the control end of the seventeenth transistor M N3 . The second end of the eighteenth transistor M N4 is connected to the second end of the nineteenth transistor M N3 . The second end of the eighteenth transistor M N3 is also grounded. The control end of the eighteenth transistor M N4 is connected to its first end and the control end of the nineteenth transistor M

[0070] Specifically, the error amplification circuit 5 is divided into two parts: an internal soft start circuit 51 and an EA core circuit 52. The EA core circuit 52 has a total of four input ends, where MP8 and MP9 are negative input ends, and MP10 and MP11 are positive input ends. The gate of MP8 is connected to VDD, and this transistor is always in the cut-off state for the matching of the input pair transistors to reduce the offset voltage. MP10 and MP11 are in a competitive relationship. The smaller the gate voltage of them, the more current is diverted. For example, when SS1 < SS_REF, at this time, the MP10 transistor diverts most of the current, and MP11 is approximately cut off. Therefore, under the action of EA, VFB will always follow the smaller one of SS1 and SS_REF.

[0071] When the system is just powered on, the reference voltage is first established before the minimum voltage selection circuit 4 works properly. SS_REF = VREF_DIV, and the magnitude of the SS1 voltage is approximately 0. At this time, MP9 and MP10 play a major role. The size of MP9 is designed to be larger than that of MP10. Since both the positive and negative input ends of the EA are 0 at this time, the output voltage of the operational amplifier can be maintained at a low level, thus avoiding current surges.

[0072] Before the soft start ends, the soft start determination signal SS_Flag is at a low level, turning on switches S1 and S2. The built-in soft start circuit 51 composed of MP2, MP6, and MP7 injects a current that decreases as SS1 increases into the drain of MP10 through switch S2, which is equivalent to adding a negative offset voltage to the positive input terminal of the op amp. This will ensure that VFB follows SS_REF but is less than SS_REF, which will further reduce the risk of current surges.

[0073] Figure 7 The figure is a startup waveform of the switching power supply after the soft start circuit of this embodiment is adopted. It can be seen that the output voltage starts smoothly and the inductor current has almost no surge.

[0074] In this embodiment, a driving circuit is provided. Figure 8 As shown, it includes: the soft start circuit and PWM module 6 of the above embodiment and any optional implementation manner thereof. The output end of the soft start circuit is connected to the input end of the PWM module 6; the output end of the PWM module 6 is connected to the electronic switch in the switching power supply; the PWM module 6 generates a switching signal based on the output voltage of the error amplifier circuit 5, and the switching signal is used to soft start the electronic switch in the switching power supply and control the on-off state of the electronic switch.

[0075] Specifically, Figure 8 The soft start principle of the soft start circuit in has been described in detail and will not be repeated here.

[0076] In the present embodiment, a switching power supply is provided, comprising: a driving circuit and a switching power supply body of the above embodiment, wherein the output end of the soft start circuit is connected to the input end of the PWM module 6; the output end of the PWM module 6 is connected to the electronic switch in the switching power supply body; the PWM module 6 generates a switching signal based on the output voltage of the error amplifier circuit 5, and the switching signal is used to soft-start the electronic switch in the switching power supply body and control the on-off state of the electronic switch.

[0077] Optionally, the switching power supply is a DC-DC converter, which may be a BUCK circuit, a BOOST circuit, a flyback circuit, etc., which is not limited here.

[0078] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A soft start circuit, characterized in that: include: Fast soft start module, slow soft start module, soft start discrimination module, minimum voltage selection circuit, error amplification circuit, among which, The output end of the fast soft start module is connected to the first input end of the soft start determination module, and the fast soft start module is used to output a fast start voltage; The output end of the slow soft start module is connected to the second input end of the soft start determination module and the first input end of the minimum voltage selection circuit, and the slow soft start module is used to output a slow start voltage; the rising slope of the fast start voltage is greater than the rising slope of the slow start voltage; The third input terminal and the fourth input terminal of the soft start determination module are respectively input with a high threshold voltage and a low threshold voltage, and the output terminal of the soft start determination module is connected with the control terminal of the error amplifier circuit; the soft start determination module is used to generate a soft start end determination signal according to the fast start voltage and the slow start voltage, and the soft start end determination signal is used to control the start and stop of the error amplifier circuit; The reference voltage is input to the second input terminal of the minimum voltage selection circuit, the output terminal of the minimum voltage selection circuit is connected to the first positive input terminal of the error amplifier circuit, and the minimum voltage selection circuit is used to output the smaller of the slow start voltage and the divided voltage of the reference voltage; The second positive input terminal of the error amplifier circuit is connected to the output terminal of the fast soft start module, the negative input terminal of the error amplifier circuit inputs the feedback voltage, the output terminal of the error amplifier circuit is connected to the input terminal of the external PWM module, the PWM module generates a switch signal based on the output voltage of the error amplifier circuit, and the switch signal is used to control the on-off state of the electronic switch in the switching power supply; the feedback voltage is the output voltage of the switching power supply; After the system is powered on, the fast start voltage controls the soft start of the error amplifier circuit; Before the soft start is completed and after the error amplifier circuit has completed the soft start, the error amplifier circuit controls the feedback voltage to follow the smaller one of the fast start voltage and the output voltage of the minimum voltage selection circuit; After a system fault occurs and is resolved, the error amplifier circuit controls the feedback voltage to follow the fast start voltage for rapid recovery; The fast soft start module includes: a first current source, a first start capacitor, and a first transistor, wherein the input end of the first current source inputs a supply voltage, the output end of the first current source is connected to the first end of the first start capacitor and the first end of the first transistor; the second end of the first transistor is connected to the second end of the first start capacitor, the second end of the first transistor is also grounded, and the control end of the first transistor inputs a control command; the first end of the first start capacitor is connected to the first input end of the soft start determination module and the second positive input end of the error amplifier circuit; when the system fails or is not powered on, the control command pulls down the fast start voltage; when the system is not faulty and is powered on, the control command pulls up the fast start voltage; The slow soft start module includes: a second current source, a second start capacitor, and a second transistor, wherein the input end of the second current source inputs a supply voltage, the output end of the second current source is connected to the first end of the second start capacitor and the first end of the second transistor; the second end of the second transistor is connected to the second end of the second start capacitor, the second end of the second transistor is also grounded, and the control end of the second transistor inputs a control command; the first end of the second start capacitor is connected to the second input end of the soft start determination module and the first input end of the minimum voltage selection circuit; when the system is not powered on, the control command pulls down the fast start voltage; when the system is powered on, the control command pulls up the fast start voltage; The soft start judgment module circuit includes: a selector, a first comparator, a first NOT gate and a second NOT gate, wherein the first input end of the selector inputs the high threshold voltage, and the second input end of the selector inputs the low threshold voltage; the first positive input end of the first comparator inputs the fast start voltage, the second positive input end of the first comparator inputs the slow start voltage, the negative input end of the first comparator is connected to the output end of the selector, and the output end of the first comparator is connected to the input end of the first NOT gate; the output end of the first NOT gate is connected to the input end of the second NOT gate and the control end of the selector, and the output end of the second NOT gate is connected to the control end of the error amplifier circuit; when the soft start is not completed and the system is not faulty, the selector outputs the high threshold voltage, and the soft start end judgment signal is a low level; when the fast start voltage and the slow start voltage are higher than the high threshold voltage, the first comparator outputs a high level, the soft start end judgment signal is a high level, and the selector outputs the low threshold voltage; when the system fails, the first comparator outputs a low level, the soft start end judgment signal is a low level, and the selector outputs the high threshold voltage; The minimum voltage selection circuit includes: a second comparator, a third transistor, a fourth transistor, a first resistor, a second resistor, a third resistor, and a first capacitor, wherein the slow start voltage is input to the negative input terminal of the second comparator; the first terminal of the third transistor is connected to the first terminal of the first resistor, the second terminal of the fourth transistor, the first terminal of the second resistor, and the second terminal of the third resistor, the second terminal of the third transistor is connected to the second terminal of the second resistor, and the second terminal of the third transistor is also grounded, the control terminal of the third transistor is connected to the second terminal of the first resistor through the first capacitor, and the control terminal of the third transistor is also connected to the output terminal of the second comparator; the first terminal of the fourth transistor is input to the supply voltage, and the control terminal of the fourth transistor is input to the control voltage; the first terminal of the third resistor is input to the reference voltage, and the second terminal of the third resistor is connected to the positive input terminal of the second comparator; when the slow start voltage is less than the divided voltage of the reference voltage, the third transistor is turned on, and the slow start voltage is input to the first positive input terminal of the error amplifier circuit; When the slow start voltage is greater than the divided voltage of the reference voltage, the third transistor is turned off, and the divided voltage of the reference voltage is input to the first positive input terminal of the error amplifier circuit; The error amplifier circuit includes: a built-in soft start circuit and an EA core circuit, wherein the first control terminal of the built-in soft start circuit inputs the soft start end judgment signal, the second control terminal of the built-in soft start circuit inputs the slow start voltage, the third control terminal of the built-in soft start circuit inputs the soft start end judgment signal, the input terminal of the built-in soft start circuit inputs the power supply voltage, the first output terminal of the built-in soft start circuit is connected to the first control terminal of the EA core circuit, the second output terminal of the built-in soft start circuit is connected to the first input terminal of the EA core circuit, and the third output terminal of the built-in soft start circuit is grounded; the second control terminal of the EA core circuit inputs the control voltage, the first output terminal of the built-in soft start circuit is connected to the first control terminal of the EA core circuit, and the second output terminal of the built-in soft start circuit is connected to the first input terminal of the EA core circuit. The feedback voltage is input into the third control terminal, the fast start voltage is input into the fourth control terminal of the EA core circuit, the fifth control terminal of the EA core circuit is connected to the output terminal of the fast soft start module, the supply voltage is input into the second input terminal of the EA core circuit, the first output terminal of the EA core circuit is connected to the PWM module, and the second output terminal of the EA core circuit is grounded; when the soft start end judgment signal is at a low level, the soft start end judgment signal controls the built-in soft start circuit to turn on, and the built-in soft start circuit injects a negative offset voltage into the first input terminal of the EA core circuit; when the soft start end judgment signal is at a high level, the soft start end judgment signal controls the built-in soft start circuit to turn off.

2. The soft start circuit according to claim 1, characterized in that: The built-in soft start circuit includes: a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a third current source, a first controllable switch and a second controllable switch, wherein: The first end of the fifth transistor inputs the supply voltage, the second end of the fifth transistor is connected to the first end of the third current source and the first end of the sixth transistor, and the control end of the fifth transistor is connected to the second end of the fifth transistor, the control end of the sixth transistor, and the first control end of the EA core circuit; The second end of the sixth transistor is connected to the first end of the seventh transistor and the first end of the eighth transistor respectively through the first controllable switch; The second end of the seventh transistor is connected to the first end thereof and the second end of the third current source, and the second end of the seventh transistor is also grounded; The second end of the eighth transistor is connected to the first input end of the EA core circuit through the second controllable switch; The control end of the first controllable switch inputs the soft start end judgment signal; The control end of the second controllable switch inputs the slow start voltage; When the soft start end judgment signal is at a low level, the soft start end judgment signal controls the first controllable switch and the second controllable switch to be turned on; when the soft start end judgment signal is at a high level, the soft start end judgment signal controls the first controllable switch and the second controllable switch to be turned off.

3. The soft start circuit according to claim 2, characterized in that: The EA core circuit includes: a ninth transistor, a tenth transistor, an eleventh transistor, a twelfth transistor, a thirteenth transistor, a fourteenth transistor, a fifteenth transistor, a sixteenth transistor, a seventeenth transistor, an eighteenth transistor, and a nineteenth transistor, wherein: The first end of the ninth transistor inputs the supply voltage, the second end of the ninth transistor is connected to the first end of the sixteenth transistor, and the control end of the ninth transistor is connected to the control end of the eleventh transistor; The first end of the tenth transistor inputs the supply voltage, the second end of the tenth transistor is connected to the first end of the twelfth transistor, the first end of the thirteenth transistor, the first end of the fourteenth transistor, and the control end of the fifteenth transistor, and the control end of the tenth transistor is connected to the control end of the fifth transistor; The first end of the eleventh transistor inputs the supply voltage, and the second end of the eleventh transistor is connected to the first end of the nineteenth transistor and the PWM module; The second end of the twelfth transistor is connected to the first end of the seventeenth transistor, and a control voltage is input to the control end of the twelfth transistor; the twelfth transistor is always in a cut-off state; The second end of the thirteenth transistor is connected to the first end of the seventeenth transistor, and the control end of the thirteenth transistor inputs the feedback voltage; The second end of the fourteenth transistor is connected to the first end of the eighteenth transistor, the second end of the fourteenth transistor is also connected to the second end of the eighth transistor through the second controllable switch, and the control end of the fourteenth transistor inputs the fast start voltage; the size of the thirteenth transistor is larger than the size of the fourteenth transistor; The second end of the fifteenth transistor is connected to the first end of the eighteenth transistor, and the control end of the fifteenth transistor is connected to the output end of the fast soft start module; The second end of the sixteenth transistor is connected to the second end of the seventeenth transistor, the second end of the sixteenth transistor is also grounded, and the control end of the sixteenth transistor is connected to the first end of the seventeenth transistor and the control end of the seventeenth transistor; The second end of the eighteenth transistor is connected to the second end of the nineteenth transistor, the second end of the eighteenth transistor is also grounded, and the control end of the eighteenth transistor is connected to the first end thereof and the control end of the nineteenth transistor.

4. A driving circuit, characterized in that: include: The soft start circuit and PWM module according to any one of claims 1 to 3, wherein: The output end of the soft start circuit is connected to the input end of the PWM module; The output end of the PWM module is connected to the electronic switch in the switching power supply; The PWM module generates a switch signal based on the output voltage of the error amplifier circuit. The switch signal is used to soft-start an electronic switch in the switching power supply and control the on / off state of the electronic switch.

5. A switching power supply, characterized in that: include: The drive circuit and the switching power supply body as claimed in claim 4, wherein: The output end of the PWM module is connected to the electronic switch in the switching power supply body; The PWM module generates a switch signal based on the output voltage of the error amplifier circuit. The switch signal is used to soft-start the electronic switch in the switching power supply body and control the on / off state of the electronic switch.

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