A soft start circuit based on voltage comparison

Abstract

The utility model provides a kind of slow start circuit based on voltage comparison, including input, output, input voltage sampling module, reference voltage module, comparison module, control module, current limiting module, energy storage module. It is realized automatic control by the comparison of input sampling voltage signal and reference voltage signal, without MCU participation, simplify circuit structure and reduce cost, solve the problem of complexity and high cost of existing MCU scheme. And utilize comparison module dynamic control switch tube state, avoid the working loss and thermal inertia problem of thermistor scheme, improve energy efficiency and support frequent start-stop, current limiting module and energy storage module synergistic effect, effectively inhibit impact current in power-on moment, protect power supply and load equipment.

Description

Technical Field

[0001] This utility model relates to the field of circuit protection technology, and in particular to a soft-start circuit based on voltage comparison. Background Technology

[0002] In power supply circuit systems, a stable power supply to electronic devices is one of the key factors ensuring their normal operation. To guarantee the stability of the power supply, most electronic devices typically use large capacitors for filtering at the power input. This filtering method can effectively smooth fluctuations in the power supply voltage and provide a stable DC power supply to the device. However, this design also brings a significant problem: when the device is powered on, the capacitor's initial voltage is zero, and the capacitor begins to charge. Because the capacitor's internal resistance is very small, it is essentially in a short-circuit state at the moment of power-on, resulting in a very large inrush current. This inrush current not only puts enormous stress on the power supply circuit but may also damage the mainboard of the control device. This problem is particularly prominent in devices with high requirements for power supply stability, such as the DC brushless electronic water pump involved in this patent.

[0003] To address this issue, there are currently two main design schemes for soft-start circuits. The first scheme involves detecting the input voltage through a sampling circuit and transmitting the detected signal to a microcontroller (MCU) for processing. The MCU controls the switching time of the MOSFET based on the detected voltage signal, thereby achieving the purpose of soft start. However, the disadvantage of this scheme is that the circuit design is relatively complex, requiring additional sampling circuits and a microcontroller for signal processing. This not only increases the design difficulty but also raises the cost, limiting its use in some cost-sensitive applications.

[0004] The second approach utilizes the temperature characteristics of a thermistor to limit the inrush current at power-on. At the moment of power-on, the thermistor's resistance is high, effectively limiting the inrush current. As current flows through the thermistor and heats it, its resistance gradually decreases, and the circuit eventually enters normal operating mode. While this approach is relatively simple, it has significant drawbacks. First, the thermistor incurs substantial operating losses during normal operation, reducing power supply efficiency and potentially increasing heat generation in the device. Second, due to thermal inertia, the thermistor's resistance cannot quickly return to its initial state when power is interrupted and then restored during normal operation, thus failing to achieve the desired soft-start effect. This is particularly disadvantageous in devices requiring frequent start-stop cycles.

[0005] In summary, existing soft-start circuit solutions are either complex and costly, or suffer from high operating losses and are unable to effectively handle frequent start-stop cycles. Utility Model Content

[0006] To address the aforementioned problems, the purpose of this invention is to provide a voltage comparison-based soft-start circuit. Voltage comparison enables automatic control without the need for an MCU, simplifying the circuit structure and reducing costs. This solves the problems of complexity and high cost associated with existing MCU solutions. Furthermore, the comparator module dynamically controls the switching transistor's state, avoiding the operating losses and thermal inertia issues of thermistor solutions, improving energy efficiency, and supporting frequent start-stop operations.

[0007] This utility model is achieved through the following technical solution:

[0008] A voltage comparison-based soft-start circuit includes:

[0009] The input voltage sampling module is used to sample the circuit input terminal in real time and output the sampled voltage signal;

[0010] The reference voltage module is used to output a stable reference voltage signal;

[0011] The comparison module has its input terminals connected to the output terminals of the input voltage sampling module and the reference voltage module, respectively, and is used to compare the magnitudes of the sampled voltage signal and the reference voltage signal and output a control signal.

[0012] The control module includes a first switch and a second switch. The control terminal of the first switch is connected to the output terminal of the comparison module, and the output terminal of the first switch is connected to the control terminal of the second switch. When the sampled voltage signal is less than the reference voltage signal, the first switch is turned on to control the second switch to turn off; when the sampled voltage signal is greater than the reference voltage signal, the first switch is turned off to control the second switch to turn on. The two terminals of the first switch are connected in parallel between the positive and negative terminals of the circuit input, and the two terminals of the second switch are connected in series with the negative terminal of the circuit output.

[0013] A current limiting module is connected in parallel between the two terminals of the first switching transistor to limit the current at the moment of power-on.

[0014] The energy storage module is connected in parallel between the positive and negative terminals of the circuit output to absorb energy at the moment of power-on.

[0015] Furthermore, the input voltage sampling module includes a first voltage divider resistor and a second voltage divider resistor, which are connected in series between the positive and negative terminals of the circuit input terminal. The common terminal of the first voltage divider resistor and the second voltage divider resistor is the output terminal of the input voltage sampling module.

[0016] Furthermore, the reference voltage module includes a current-limiting resistor and a Zener diode, which are connected in series between the positive and negative terminals of the circuit input. The common terminal of the current-limiting resistor and the Zener diode is the output terminal of the reference voltage module.

[0017] Furthermore, the comparison module includes a voltage comparator, the common terminal of the first voltage divider resistor and the second voltage divider resistor is connected to the non-inverting input terminal of the voltage comparator, the common terminal of the current limiting resistor and the Zener diode is connected to the inverting input terminal of the voltage comparator, and the output terminal is connected to the control module.

[0018] Furthermore, the first switching transistor is a PNP transistor, and the emitter of the first switching transistor is connected to the positive terminal of the circuit input and the control terminal of the second switching transistor, respectively. The collector of the first switching transistor is connected to the negative terminal of the circuit input. The emitter of the first switching transistor is connected to the positive terminal of the circuit input through a pull-up resistor.

[0019] Furthermore, the second switch is an NMOS transistor, with its source connected to the negative input terminal of the circuit, its drain connected to the negative output terminal of the circuit, and its gate connected to the emitter of the first switch.

[0020] Furthermore, the control module also includes a TVS diode connected between the gate of the second switching transistor and the negative terminal of the power supply to limit the gate voltage; the cathode of the TVS diode is connected to the gate of the MOS transistor.

[0021] Furthermore, the current limiting module includes a power resistor connected in parallel between the two terminals of the second switching transistor.

[0022] Furthermore, the energy storage module includes an electrolytic capacitor connected in parallel between the positive and negative terminals of the circuit output terminal. The positive terminal of the electrolytic capacitor is connected to the positive terminal of the circuit output terminal, and the negative terminal of the circuit output terminal is grounded.

[0023] Furthermore, the soft-start circuit also includes a transient voltage suppression diode connected in parallel between the positive and negative terminals of the circuit input to suppress surge voltage at the input; and / or, it also includes a reverse connection protection diode connected in series with the positive terminal of the circuit input to prevent reverse power connection.

[0024] Compared with the prior art, the technical solution of this utility model and its beneficial effects are as follows:

[0025] (1) At the moment of power-on at the input terminal of this utility model, due to the large current generated by the charging of the energy storage module, the input terminal voltage is pulled down. The sampled voltage signal is less than the reference voltage signal, which controls the first switch to turn on and the second switch to turn off. The large current at the moment of power-on passes through the first switch to the current limiting module, which limits it to a suitable range, thereby suppressing the large current surge. After the energy storage module finishes charging, the output terminal voltage recovers, and the voltage signal collected by the input voltage sampling module rises. The sampled voltage signal is greater than the reference voltage signal, so the first switch turns off and the second switch turns on. The current in the circuit passes through the second switch to the energy storage module, and the current limiting module is bypassed, thereby reducing power consumption. Automatic control is achieved through voltage comparison, without the need for MCU participation, simplifying the circuit structure.

[0026] (2) The control module of this utility model also includes a TVS transistor connected between the gate of the second switching transistor and the negative terminal of the power supply, which is used to limit the gate voltage and protect the gate of the NMOS transistor from voltage spike damage. Attached Figure Description

[0027] Figure 1 This is a block diagram of a voltage comparison-based soft-start circuit provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of a voltage comparison-based soft-start circuit provided in an embodiment of this utility model. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. It should be understood that the specific embodiments described herein are only used to explain this utility model and are not intended to limit this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0030] See Figure 1 A voltage comparison-based soft-start circuit includes an input terminal, an output terminal, an input voltage sampling module, a reference voltage module, a comparison module, a control module, a current limiting module, and an energy storage module. The input voltage sampling module is connected to the input terminal and is used to sample the circuit input in real time and output a sampled voltage signal. The reference voltage module is used to output a stable reference voltage signal. The input terminal of the comparison module is connected to the output terminals of both the input voltage sampling module and the reference voltage module, and is used to compare the magnitudes of the sampled voltage signal and the reference voltage signal and output a control signal.

[0031] The control module includes a first switch and a second switch. The control terminal of the first switch is connected to the output terminal of the comparator module, and the output terminal of the first switch is connected to the control terminal of the second switch. When the sampled voltage signal is less than the reference voltage signal, the first switch is turned on, controlling the second switch to turn off; when the sampled voltage signal is greater than the reference voltage signal, the first switch is turned off, controlling the second switch to turn on. The two terminals of the first switch are connected in parallel between the positive and negative terminals of the circuit input, and the two terminals of the second switch are connected in series between the negative terminal of the circuit output. A current limiting module is connected between the two terminals of the second switch to limit the current at power-on. An energy storage module is connected in parallel between the positive and negative terminals of the circuit output to absorb energy at power-on.

[0032] At the moment of power-on, the energy storage module generates a large current during charging, pulling down the input voltage. This reduces the sampled voltage signal acquired by the input voltage sampling module. This lower sampled voltage signal and the reference voltage signal are input to the comparator module. Since the sampled voltage signal is lower than the reference voltage signal, the first switch is turned on and the second switch is turned off. The large current at power-on passes through the first switch to the current limiting module, where it is limited to a suitable range, thus suppressing the large current surge. "Suitable" here refers to the ability to reasonably select the resistance value of the current limiting module, thereby limiting the current to a value range that will not damage the circuit or subsequent load.

[0033] After the energy storage module is fully charged, the output voltage recovers, the voltage signal collected by the input voltage sampling module increases, and the sampled voltage signal is greater than the reference voltage signal. The first switch is turned off and the second switch is turned on. The current of the circuit flows through the second switch to the energy storage module, and the current limiting module is bypassed, thereby reducing power consumption.

[0034] This invention achieves automatic control through voltage comparison, eliminating the need for an MCU, simplifying the circuit structure and reducing costs, and solving the problems of complexity and high cost associated with existing MCU solutions. Furthermore, it utilizes a comparator module to dynamically control the switching transistor state, avoiding the operating losses and thermal inertia issues of thermistor solutions, improving energy efficiency and supporting frequent start-stop operations. This makes it particularly suitable for electronic devices requiring frequent start-stop operations, such as DC brushless electric water pumps. The current limiting module and energy storage module work together to effectively suppress inrush current at power-on, protecting the power supply and load equipment.

[0035] The input voltage sampling module in this embodiment includes a first voltage divider resistor R1 and a second voltage divider resistor R2, connected in series between the positive and negative terminals of the circuit input. The common terminal of the first voltage divider resistor R1 and the second voltage divider resistor R2 is the output terminal of the input voltage sampling module. The input voltage sampling module uses a resistor divider, which is simple and reliable in structure, samples the input voltage in real time, provides an accurate signal for the comparison module, and ensures the accuracy of soft-start triggering.

[0036] The reference voltage module includes a current-limiting resistor R3 and a Zener diode D3, connected in series between the positive and negative terminals of the circuit input. The common terminal of the current-limiting resistor R3 and the Zener diode D3 is the output terminal of the reference voltage module. Because the Zener diode D3 has a very stable reverse breakdown voltage, the voltage across the Zener diode D3 will maintain a relatively fixed value, which is the reference voltage. This means it is unaffected by voltage fluctuations at the input terminal, enhancing the reliability of soft-start.

[0037] The comparison module includes a voltage comparator U1. The common terminal of the first voltage divider resistor R1 and the second voltage divider resistor R2 is connected to the non-inverting input terminal of the voltage comparator U1. The common terminal of the current limiting resistor R3 and the Zener diode D3 is connected to the inverting input terminal of the voltage comparator U1. The output terminal is connected to the control module. The voltage comparator U1 directly compares the sampled voltage signal with the reference voltage signal, which has a fast response speed, high control accuracy, and avoids the signal processing delay of the MCU solution.

[0038] In this embodiment, the first switch Q1 is a PNP transistor. The emitter of the first switch Q1 is connected to both the positive terminal of the circuit input and the control terminal of the second switch Q2. The collector of the first switch Q1 is connected to the negative terminal of the circuit input. The emitter of the first switch Q1 is connected to the positive terminal of the circuit input through a pull-up resistor R4. The second switch Q2 is an NMOS transistor. The source of the second switch Q2 is connected to the negative terminal of the circuit input, the drain is connected to the negative terminal of the circuit output, and the gate is connected to the emitter of the first switch Q1.

[0039] When the sampled voltage signal is less than the reference voltage signal, the voltage comparator U1 outputs a low level to control the first switch Q1 to turn on, the gate voltage of the second switch Q2 is pulled low, and the second switch Q2 is turned off. The current flows through the first switch Q1 to the current limiting module, where it is limited. The current limiting module can use a power resistor R6. When the sampled voltage signal is greater than the reference voltage signal, the voltage comparator U1 outputs a high level to control the first switch Q1 to turn off, the gate of the second switch Q2 is high, and the second switch Q2 is turned on. The current flows through the second switch Q2, and the power resistor R6 is bypassed. The second switch Q2 has a low internal resistance and low power consumption during normal operation, which can effectively reduce heat generation and power loss, solving the problem of continuous high power loss in thermistor solutions. The gate is controlled by the first switch, resulting in good logic matching.

[0040] In this embodiment, the energy storage module includes an electrolytic capacitor EC1, which is connected in parallel between the positive and negative terminals of the circuit output terminal. The positive terminal of the electrolytic capacitor EC1 is connected to the positive terminal of the circuit output terminal, and the negative terminal of the circuit output terminal is grounded.

[0041] The control module also includes a TVS diode connected between the gate of the second switching transistor and the negative terminal of the power supply to limit the gate voltage. The cathode of the TVS diode is connected to the gate of the MOSFET. The TVS diode protects the gate of the NMOS transistor from voltage spike damage, improves the reliability of the circuit under surge conditions, and extends the device life.

[0042] The circuit also includes a protection module, which includes a transient voltage suppression diode D1 connected in parallel between the positive and negative terminals of the circuit input to suppress surge voltage at the input; and / or a reverse connection protection diode D2 connected in series with the positive terminal of the circuit input to prevent reverse power connection.

[0043] The foregoing description illustrates and describes preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the present invention through the foregoing teachings or related technical or knowledge. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A soft-start circuit based on voltage comparison, characterized in that, include: The input voltage sampling module is used to sample the circuit input terminal in real time and output the sampled voltage signal; The reference voltage module is used to output a stable reference voltage signal; The comparison module has its input terminals connected to the output terminals of the input voltage sampling module and the reference voltage module, respectively, and is used to compare the magnitudes of the sampled voltage signal and the reference voltage signal and output a control signal. The control module includes a first switch and a second switch. The control terminal of the first switch is connected to the output terminal of the comparison module, and the output terminal of the first switch is connected to the control terminal of the second switch. When the sampled voltage signal is less than the reference voltage signal, the first switch is turned on to control the second switch to turn off; when the sampled voltage signal is greater than the reference voltage signal, the first switch is turned off to control the second switch to turn on. The two terminals of the first switch are connected in parallel between the positive and negative terminals of the circuit input, and the two terminals of the second switch are connected in series with the negative terminal of the circuit output. A current limiting module is connected in parallel between the two terminals of the first switching transistor to limit the current at the moment of power-on. The energy storage module is connected in parallel between the positive and negative terminals of the circuit output to absorb energy at the moment of power-on.

2. The soft-start circuit according to claim 1, characterized in that, The input voltage sampling module includes a first voltage divider resistor and a second voltage divider resistor, which are connected in series between the positive and negative terminals of the circuit input terminal. The common terminal of the first voltage divider resistor and the second voltage divider resistor is the output terminal of the input voltage sampling module.

3. The soft-start circuit according to claim 1, characterized in that, The reference voltage module includes a current-limiting resistor and a Zener diode, which are connected in series between the positive and negative terminals of the circuit input. The common terminal of the current-limiting resistor and the Zener diode is the output terminal of the reference voltage module.

4. The soft-start circuit according to claim 1, characterized in that, The comparison module includes a voltage comparator. The common terminal of the first voltage divider resistor and the second voltage divider resistor is connected to the non-inverting input terminal of the voltage comparator. The common terminal of the current limiting resistor and the Zener diode is connected to the inverting input terminal of the voltage comparator. The output terminal is connected to the control module.

5. The soft-start circuit according to claim 1, characterized in that, The first switching transistor is a PNP transistor. The emitter of the first switching transistor is connected to the positive terminal of the circuit input and the control terminal of the second switching transistor, respectively. The collector of the first switching transistor is connected to the negative terminal of the circuit input. The emitter of the first switching transistor is connected to the positive terminal of the circuit input through a pull-up resistor.

6. The soft-start circuit according to claim 5, characterized in that, The second switch is an NMOS transistor. The source of the second switch is connected to the negative terminal of the circuit input, the drain is connected to the negative terminal of the circuit output, and the gate is connected to the emitter of the first switch.

7. The soft-start circuit according to claim 6, characterized in that, The control module also includes a TVS diode connected between the gate of the second switching transistor and the negative terminal of the power supply to limit the gate voltage; the cathode of the TVS diode is connected to the gate of the MOS transistor.

8. The soft-start circuit according to claim 1, characterized in that, The current limiting module includes a power resistor, which is connected in parallel between the two terminals of the second switching transistor.

9. The soft-start circuit according to claim 1, characterized in that, The energy storage module includes an electrolytic capacitor connected in parallel between the positive and negative terminals of the circuit output terminal. The positive terminal of the electrolytic capacitor is connected to the positive terminal of the circuit output terminal, and the negative terminal of the circuit output terminal is grounded.

10. The soft-start circuit according to claim 1, characterized in that, It also includes a transient voltage suppression diode connected in parallel between the positive and negative terminals of the circuit input to suppress surge voltage at the input; and / or, it also includes a reverse connection protection diode connected in series with the positive terminal of the circuit input to prevent reverse power supply connection.

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