Self-adaptive soft start control circuit and control method based on slope detection

Abstract

The invention discloses a self-adaptive soft start control circuit and method based on slope detection. The circuit comprises an operational amplifier AMP, a comparator COMP, RS latches 1 and 2, a counter Counter, an AND gate AND, a resistor, a capacitor and a current source ISS. According to the invention, the dynamic monitoring of the load change and the real-time feedback of the load state are introduced, so that the control parameters in the soft start process are optimized. According to the method, the soft start time and the voltage rise rate can be adjusted in real time when the load suddenly changes, slow rise of the current is ensured, and current surge during starting is avoided. In this way, the stability and the dynamic response capability in the soft start process are remarkably improved. The performance limitation of traditional soft start control under load change is overcome, the starting stability and the anti-jamming capability of the system are remarkably improved, it is ensured that the power converter can be stably started in a complex load environment, and the reliability and the performance of the system are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power management, and particularly relates to a self-adaptive soft start control circuit based on slope detection and a control method. BACKGROUND

[0002] Soft start is a control technology commonly used in power management systems, aiming to suppress sudden current changes and prevent current surges and thermal stress on devices during the initial power converter power-on or restart by gradually increasing the output voltage or adjusting the duty cycle.

[0003] During the startup phase, since the output voltage has not been established, the large capacitance at the load end exhibits low impedance characteristics, and the system is equivalent to a short circuit or heavy load state. If direct power supply is used, it is easy to cause the converter output to have a large instantaneous current, thereby causing device damage, overheating, and even breakdown. To avoid this problem, the soft start mechanism slowly rises the reference voltage, limits the switch tube conduction time, or introduces current limiting means, so that the output voltage is smoothly established within hundreds of microseconds to milliseconds, thereby effectively slowing down the startup current rise rate, reducing system transient stress, and improving the stability and reliability of the entire power system.

[0004] In the soft start control of power converters, there are mainly two implementation methods: built-in soft start circuit and external soft start circuit. The built-in soft start circuit integrates the soft start function into the control chip, which can simplify system design, reduce external components, and thus save space and cost. However, this method has poor flexibility and cannot adjust the soft start time according to the load change, which may cause slow startup at light load or large current impact at heavy load.

[0005] In contrast, the external soft start circuit provides higher flexibility. By using external capacitors or other components, designers can adjust the soft start time according to specific application requirements, thereby optimizing the startup performance of the system. This method can more accurately control the startup process and adapt to different load conditions.

[0006] Although the built-in soft start circuit has certain advantages in simplifying design and saving space, in applications that require flexible adjustment of soft start time to adapt to different loads, the external soft start circuit performs better. In order to combine the advantages of both, developing a self-adaptive soft start circuit and its control method that can automatically adjust the soft start parameters according to the load condition has become an important development direction in current power management technology.

[0007] The existing soft start circuit has the problems of lack of flexibility, fixed startup time, and high design complexity. The existing soft start circuit cannot dynamically adjust the soft start time under different load conditions, resulting in slow startup at light load or large current impact at heavy load. SUMMARY

[0008] The present application aims to provide a slope detection based adaptive soft start control circuit and control method for improving the start performance of power converter, reducing the current impact in the start process, and improving system stability and reliability.

[0009] The slope detection based adaptive soft start control circuit of the present application is applied to a BUCK circuit, and comprises an operational amplifier AMP, a comparator COMP, RS latches Latch1 and Latch2, a counter Counter, an AND gate, resistors, capacitors and a current source ISS. The input end of the counter Counter and the input end of the AND gate are respectively connected to an input clock signal, the enable end of the counter Counter is grounded through the R port of Latch1, the S port of Latch1 is connected to the output OUT of the counter Counter, and the output end of Latch1 is connected to the other input end of the AND gate.

[0010] Further, the resistors comprise R1 and R2, the capacitors comprise C1, C2, C3 and Cout, one end of the capacitor C1 is connected to the detection signal VL, one end of the resistor R2 is connected to the capacitor C2 and the negative end of the operational amplifier AMP, and the other end of the resistor R2 is connected to the resistor R1.

[0011] Further, the capacitors further comprise C3 and Cout, and the adaptive soft start control circuit further comprises an NMOS tube NM1, the R end of the Latch2 is grounded, the output Q is connected to the gate of the NMOS tube NM1, the source of the NMOS tube NM1 is grounded, the drain of the NMOS tube NM1 is connected to the capacitor C3, one end of the capacitor Cout is grounded, and the other end of the capacitor Cout is connected to the capacitor C3 and the current source ISS, thereby generating the output signal VSS.

[0012] Further, the positive end of the operational amplifier AMP is connected to a bias voltage V_bias.

[0013] Further, the negative end of the comparator COMP is connected to a reference voltage Vref1.

[0014] The present application further discloses a control method of the adaptive soft start control circuit. LThe slope is detected by a differentiator circuit composed of C1, R1 and AMP, which uses the current flowing through the capacitor and the feedback resistor of the operational amplifier to generate a proportional voltage, the output of which reflects the slope of the input signal. th When Vout>Vref1, the comparator output is high, and the signal enters the latch output NMOS transistor NM control signal Q is high, making the NMOS transistor conductive, and the capacitor C3 is connected in parallel with Cout, thereby prolonging the rising time of the soft start signal VSS.

[0015] The circuit requires detection of the slope in the first N switching cycles of soft start. If any cycle satisfies: off >S th It is determined to be a heavy load state; otherwise, it is a light load state. The control signal CLK of the lower power tube is monitored by the counter Counter. When CLK experiences N cycles, the N-bit counter outputs a high level, and the signal passes through the RS latch to output the signal After the AND gate, the enable signal of the operational amplifier AMP and the comparator COMP is generated, so that AMP and COMP only detect and compare in the first N cycles, and then adjust the soft start time.

[0016] Further, when the main switch is off, the inductor current i L The slope decreases, and according to the basic relationship of the inductor, we have: where V L is the voltage across the inductor. At the time of shutdown, the energy stored in the inductor is mainly released to the load and output capacitor because the output voltage is still low. The greater the load current and the heavier the load, the faster the discharge and the greater the slope of the decrease. Conversely, it is a light load. The decrease slope is defined as:

[0017]

[0018] where, is the derivative of the inductor current with respect to time, which represents the slope of the decrease of the inductor current during shutdown, with the unit of A / s.

[0019] Further, the output signal Vout is:

[0020]

[0021] Wherein, R1 and C1 are resistance and capacitance that constitute a differentiator; The derivative of the inductance voltage with respect to time, denoted as, represents the slope of the inductance current drop during the off period; V_bias is a bias voltage used to shift the signal to a certain level for subsequent comparison.

[0022] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0023] 1. The present application can automatically adjust the soft start time according to the load condition through adaptive control, thereby optimizing the start-up process. In addition, traditional built-in soft start circuits can usually only fix the soft start time and cannot adapt to the needs of various different loads, while external soft start circuits, although providing flexibility, increase the design and cost complexity. The adaptive control method provided by the present application can dynamically adjust the soft start parameters, avoiding these problems, simplifying the design, reducing the cost and space occupation, and improving the reliability and start-up performance of the power converter under various load conditions.

[0024] 2. Adaptive soft start control: The greatest innovation of the present application lies in providing an adaptive soft start circuit and control method that can automatically adjust the soft start parameters according to the load condition. Unlike the fixed soft start time or manual setting of the prior art, the present application can optimize the soft start process in real time according to different load changes, avoiding slow or fast start-up response.

[0025] 3. Automatic adjustment of soft start time: In the prior art, built-in soft start circuits usually cannot flexibly adjust the soft start time, while external soft start circuits, although providing higher flexibility, still require manual design and adjustment. In contrast, the present application, through adaptive control, enables the soft start time to be automatically adjusted to adapt to different load states, optimizing the system start-up performance.

[0026] 4. Reducing additional design complexity: Although external soft start circuits can provide flexibility, they also increase design and cost complexity. Through the adaptive control method of the present application, the soft start time can be automatically adjusted without increasing additional hardware design, thereby simplifying the design, reducing the cost and space occupation.

[0027] 5. The soft start control method of the present application is applicable to various power converters, including but not limited to DC-DC converters, AC-DC converters, direct current motor drive power supplies, etc. In these applications, especially in scenarios with large load changes, the present application can effectively adjust the current change during the soft start process, avoiding damage to equipment or performance degradation due to sudden current surges. This technology is widely applicable to consumer electronics, communication equipment, power electronics, electric vehicles, industrial control, etc., and has significant advantages in applications that require smooth start-up of power systems.

[0028] 6、The application optimizes the control parameters in the soft start process by introducing dynamic monitoring of load changes and real-time feedback of load status. This method can adjust the soft start time and voltage rise rate in real time when the load changes suddenly, ensuring a slow rise of current and avoiding current surges during startup. In this way, the stability and dynamic response capability of the soft start process are significantly improved. The improved method of the application overcomes the performance limitations of traditional soft start control under load changes, significantly improves the startup stability and anti-interference capability of the system, ensures smooth startup of the power converter in a complex load environment, and improves the reliability and performance of the system. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a whole circuit architecture diagram of the application. DETAILED DESCRIPTION

[0030] The technical solutions of the application will be further described below with reference to the accompanying drawings.

[0031] An adaptive soft start control method based on slope detection of the falling section is applied to a BUCK circuit, and the overall circuit framework of the method is as shown in Figure 1 , which includes resistors R1 and R2, capacitors C1, C2, C3 and Cout, an operational amplifier AMP, a comparator COMP, RS latches Latch1 and Latch2, a counter Counter, an AND gate, and a current source ISS. The signal control part is realized by the following devices: the input end of the counter Counter is connected to the input end of the AND gate to input a clock signal, the enable end of the counter is grounded through the R port of the flip-flop Latch1, the S port of the counter Latch1 is connected to the output OUT of the counter, and the output end of the Latch1 is connected to the other input end of the AND gate to generate a signal. The signal generated by the other input end of the AND gate is connected to the enable end of the operational amplifier AMP and the comparator COMP. One end of the capacitor C1 is connected to a detection signal VL, and the other end is connected to the resistor R2. The other end of the resistor R2 is connected to the resistor R1, the capacitor C2 and the negative end of the operational amplifier AMP. The positive end of the operational amplifier AMP is connected to a bias voltage V_bias. The output is connected to the resistor R1, the capacitor C2 and the positive end of the comparator COMP. The negative end of the comparator is connected to a reference voltage Vref1. The output end is connected to the S port of the RS latch Latch2, and the R port of the latch is grounded. The output Q is connected to the gate level of the NMOS tube NM1. The source of the NM1 is grounded, and the drain is connected to the capacitor C3. One end of the capacitor Cout is grounded, and the other end is connected to the capacitor C3 and the current source ISS, thereby generating an output signal VSS.

[0032] The implementation principle of the method is as follows:

[0033] The method proposes a light and heavy load identification mechanism based on the slope detection of inductance current falling section, to dynamically adjust the soft start time constant τ. At the initial stage of starting, when the main switch is off, the inductance current i L drops with a certain slope. According to the basic relationship of inductance:

[0034]

[0035] where V L is the voltage across the inductor. At the time of turning off, since the output voltage is still low, the energy stored in the inductor is mainly released to the load and output capacitor. The greater the load current (heavy load), the faster the discharge, and the greater the falling slope; otherwise, it is light load. Define the falling slope as:

[0036]

[0037] The differentiator circuit composed of C1, R1 and AMP realizes the function of slope detection. This circuit uses the current characteristics flowing through the capacitor, and uses the feedback resistor of the operational amplifier to generate a proportional voltage. The output of this circuit will reflect the slope of the input signal, and the corresponding output signal is:

[0038]

[0039] At the same time, the passive devices determine the poles and zeros of the transfer function, and must ensure the stability of the loop. Therefore, the second resistor R2 on the input path and the capacitor C2 in parallel with the feedback resistor R1 form a compensation circuit to maintain the stability of the loop.

[0040] The output signal Vout obtained is compared with the reference voltage Vref through the comparator, and the value of Vref1 corresponds to the corresponding slope threshold S th When Vout>Vref1, the comparator output is high, and the signal enters the latch output NMOS tube NM control signal Q is high, making the NMOS tube conductive, and the capacitors C3 and Cout are connected in parallel, thereby prolonging the rising time of the soft start signal VSS. When Vout<Vref1, the comparator output is low, and after the latch output NMOS tube NM control signal Q is low, the NMOS tube is cut off, so that the rising time of the soft start signal VSS remains unchanged.

[0041] The circuit requires that the slope be detected within the first N switching periods at the initial stage of soft start. If any period satisfies: off S th , it is determined as heavy load state; otherwise, it is light load state. Therefore, the control signal CLK of the lower power tube is monitored by the counter Counter, and when CLK experiences N periods, the N-bit counter outputs high level. After the RS latch, the output signal The signal and CLK pass through an AND gate to generate the enable signals of the operational amplifier AMP and the comparator COMP, so that the AMP and the COMP only detect and compare in the first N cycles, and then adjust the soft start time.

[0042] The valve combines the simple structure, fast response slope detection mechanism and adjustable soft start parameter adjustment to realize adaptive soft start control without a current detection loop, and is especially suitable for a BUCK power supply system with analog control to improve the startup performance and system robustness.

Claims

1. An adaptive soft start control circuit based on slope detection, applied to a BUCK circuit, characterized in that: It includes an operational amplifier AMP, a comparator COMP, an RS latch Latch1, Latch2, a counter Counter, an AND gate AND, a resistor, a capacitor and a current source ISS; wherein, the input end of the counter Counter and the input end of the AND gate AND are respectively connected to the input clock signal, the enable end of the counter Counter and the R port of Latch1 are grounded, the S end of Latch1 is connected to the output OUT of the counter Counter, and the output end of Latch1 is connected to the OUT of the counter Counter. The signal generated by connecting the other input terminal of the AND gate AND is connected to the enable terminal of the operational amplifier AMP and the comparator COMP; the detection signal VL is connected to the negative terminal of the operational amplifier AMP and the positive terminal of the comparator COMP respectively; the output terminal of the operational amplifier AMP is connected to the positive terminal of the comparator COMP; the output terminal of the comparator COMP is connected to the S terminal of Latch2, and the R terminal of Latch2 is connected to the capacitor and the current source ISS to generate the output signal VSS.

2. The adaptive soft start control circuit based on slope detection according to claim 1, characterized in that: The resistors include R1 and R2, and the capacitors include C1, C2, C3, and Cout; one end of the capacitor C1 is connected to the detection signal VL and the other end is connected to the resistor R2, and the other end of the resistor R2 is connected to the resistor R1, the capacitor C2, and the negative end of the operational amplifier AMP.

3. The adaptive soft start control circuit based on slope detection according to claim 1, characterized in that: The capacitor also includes C3 and Cout; the adaptive soft start control circuit also includes an NMOS transistor NM1; the R end of the latch2 is grounded, the output Q is connected to the gate of the NMOS transistor NM1, the source of NM1 is grounded, and the drain is connected to the capacitor C3; one end of the capacitor Cout is grounded, and the other end is connected to the capacitor C3 and the current source ISS, and an output signal VSS is generated at the same time.

4. The adaptive soft start control circuit based on slope detection according to claim 1, characterized in that: The positive terminal of the operational amplifier AMP is connected to a bias voltage V_bias.

5. The adaptive soft start control circuit based on slope detection according to claim 1, characterized in that: The negative terminal of the comparator COMP is connected to the reference voltage Vref1.

6. A control method based on the adaptive soft start control circuit according to claim 1, characterized in that: At the initial stage of startup, when the main switch is turned off, the inductor current i L decreases at a certain slope; the differentiator circuit composed of C1, R1, and AMP realizes the detection function of the slope. Utilizing the current characteristics flowing through the capacitor and using the operational amplifier feedback resistor to generate a proportional voltage, the output of this circuit will reflect the slope of the input signal. The output signal Vout is calculated, and the obtained output signal Vout is compared with the reference voltage Vref through a comparator. The value of Vref1 corresponds to the corresponding slope threshold S th . When Vout > Vref1, the comparator output is high level, and the signal enters the latch. The output NMOS transistor NM control signal Q is high level, making the NMOS transistor conduct, and capacitor C3 is connected in parallel with Cout, thus extending the rising time of the soft start signal VSS; when Vout < Vref1, the comparator output is low level. After passing through the latch, the output NMOS transistor NM control signal Q is low level, making the NMOS transistor cut off, so that the rising time of the soft start signal VSS remains unchanged; The circuit detects the slope in the first N switching cycles of the soft start. If any cycle satisfies: S off >S th The control signal CLK of the power tube is monitored by the counter Counter. When CLK goes through N cycles, the N-bit counter outputs a high level. The signal passes through the RS latch and outputs a signal. The signal and CLK pass through the AND gate to generate enable signals for the operational amplifier AMP and the comparator COMP, so that AMP and COMP are detected and compared only in the first N cycles, thereby adjusting the soft start time.

7. A control method according to claim 6, characterized in that: When the main switch is turned off, the inductor current i L It decreases at a certain slope, and according to the basic relationship of inductance, it is obtained: L is the voltage across the inductor. When the inductor is turned off, the output voltage is still low, and the energy stored in the inductor is mainly released to the load and output capacitor. The larger the load current and the heavier the load, the faster the discharge and the larger the falling slope. On the contrary, for light load, the falling slope is defined as: in, It is the derivative of the inductor current with respect to time, indicating the slope of the inductor current decrease during the off period, and its unit is A / s.

8. A control method according to claim 6, characterized in that: The output signal Vout is: Among them, R1 and C1 are the resistance and capacitance that constitute the differentiator; is the time derivative of the voltage across the inductor, expressed as the slope of the inductor current decrease during the off period; V_bias is the bias voltage, which is used to shift the signal to a specific level.

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