A power mosfet-based switching circuit

Abstract

The application relates to a power MOSFET-based switching circuit, which comprises an input power supply, a switch and a power MOSFET, the power supply is connected to the source of the power MOSFET through the switch, the drain of the power MOSFET is an output end and is connected to a capacitor, the front end of the switch is provided with an external power supply pin, the power MOSFET is a P-type MOSFET, and the circuit further comprises: a first regulating sub-circuit, the first regulating sub-circuit controls the power MOSFET to work in a saturation region when the switch is closed and the output end voltage is lower than a set threshold value, and the capacitor is charged with a small current; and a second regulating sub-circuit, the second regulating sub-circuit controls the power MOSFET to work in a linear region when the switch is closed and the output end voltage is greater than the set threshold value, and the capacitor is charged with a large current. Compared with the prior art, the application avoids a large drop of the voltage of the external power supply pin, and guarantees the reliability of the power supply of the switching circuit.

Description

Technical Field

[0001] This invention relates to a switching circuit, and more particularly to a switching circuit based on a power MOSFET. Background Technology

[0002] Currently, many power boards use power MOSFETs as switching circuits in their power circuits. For example... Figure 1 The diagram shows the equivalent circuit of a common switching circuit. S1 is the switch, Q1 is the power MOSFET, R1 is the equivalent parasitic resistance, and a large capacitor C1 is located after the power MOSFET. At the moment of power-on, when switch S1 closes, a large current is charged, causing a significant drop in VDD1 voltage. Figure 2 The waveform shown is the power-on voltage waveform. If other circuits are powered through VDD1 at this time, significant problems will occur due to the severe voltage drop in VDD1.

[0003] Therefore, solving the problem of voltage drop in the switching circuit at the moment of power-on is the focus of this invention. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a switching circuit based on a power MOSFET.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A switching circuit based on a power MOSFET includes an input power supply, a switch, and a power MOSFET. The power supply is connected to the source of the power MOSFET via the switch, and the drain of the power MOSFET is the output terminal and connected to a capacitor. The switch has an external power supply pin at its front end. The power MOSFET is a P-type MOSFET. The circuit also includes:

[0007] The first regulating circuit controls the power MOSFET to operate in the saturation region when the switch is closed and the output voltage is lower than a set threshold, and the capacitor is charged with a small current.

[0008] The second regulating circuit controls the power MOSFET to operate in the linear region when the switch is closed and the output voltage is greater than a set threshold, and the capacitor is charged with a large current.

[0009] Preferably, the first regulating circuit includes a voltage reference circuit, the input terminal of which is connected to the source of the power MOSFET, and the output terminal of which is connected to the gate of the power MOSFET.

[0010] Preferably, the voltage reference circuit includes a voltage reference circuit composed of TL431.

[0011] Preferably, the second regulating sub-circuit includes a voltage divider module and a regulating MOSFET. The voltage divider module is connected in parallel with a capacitor. The voltage divider module has a voltage divider output pin, which is connected to the gate of the regulating MOSFET. The drain of the regulating MOSFET is connected to the gate of the power MOSFET, and the source of the regulating MOSFET is grounded.

[0012] Preferably, the voltage divider module is a resistor voltage divider module, including a first voltage divider resistor and a second voltage divider resistor connected in series, and the series connection point of the first voltage divider resistor and the second voltage divider resistor is the voltage divider output pin.

[0013] Preferably, the regulating MOSFET is an N-type MOSFET;

[0014] Preferably, the set threshold for the output voltage is 10% of the input power supply voltage.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The present invention uses two regulating sub-circuits to regulate the working state of the power MOSFET, thereby effectively preventing the voltage of the peripheral power supply pin from dropping severely when the device is powered on, and ensuring the reliability of the circuit power supply.

[0017] (2) The first regulating circuit of the present invention is configured as a voltage reference circuit, so that the power MOSFET operates in the saturation region and the gate-source voltage V of the power MOSFET is... GS The clamp is located at a low voltage, thus enabling low-current charging. The voltage drop across the equivalent parasitic resistance at the front end of the switch is small, and the voltage drop amplitude of the output voltage of the external power supply pin is small, ensuring reliable power supply to the circuit.

[0018] (3) The second regulating sub-circuit of the present invention combines a voltage divider module and a regulating MOSFET. The operating state of the MOSFET is adjusted by the voltage division of the resistor in the voltage divider module. The time for the power MOSFET to enter the linear region can be adjusted according to the circuit operation, thus making the debugging flexible and convenient. Attached Figure Description

[0019] Figure 1 This is the equivalent circuit diagram of a common switching circuit;

[0020] Figure 2 This is a common power-on voltage waveform for switching circuits;

[0021] Figure 3 This is a circuit diagram of a power MOSFET-based switching circuit according to the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Note that the following description of the embodiments is merely illustrative and is not intended to limit its applicability or use, nor is the present invention limited to the following embodiments.

[0023] Example

[0024] like Figure 3 As shown, this embodiment provides a switching circuit based on a power MOSFET, including an input power supply, a switch, and a power MOSFET. The power supply is connected to the source of the power MOSFET through the switch, and the drain of the power MOSFET is the output terminal and connected to a capacitor. An external power supply pin is provided at the front end of the switch. The power MOSFET is a P-type MOSFET. The circuit also includes:

[0025] The first regulating circuit controls the power MOSFET to operate in the saturation region when the switch is closed and the output voltage is lower than the set threshold, and the capacitor is charged with a small current.

[0026] The second regulating circuit controls the power MOSFET to operate in the linear region when the switch is closed and the output voltage is greater than the set threshold. The capacitor is charged with a large current. The charging current here is related to the on-resistance of the MOSFET. In most applications, it is desirable for the current to be as large as possible.

[0027] The first regulating circuit includes a voltage reference circuit. The input terminal of the voltage reference circuit is connected to the source of the power MOSFET, and the output terminal is connected to the gate of the power MOSFET. The voltage reference circuit is composed of a TL431 microcontroller and includes resistors R3, R4, and R5, as well as the TL431 chip. The voltage reference circuit is a conventional circuit, specifically as follows: Figure 3 As shown in the image.

[0028] The second regulation sub-circuit includes a voltage divider module and a regulating MOSFET. The regulating MOSFET is an N-type MOSFET. The voltage divider module is connected in parallel with a capacitor. The voltage divider module has a voltage divider output pin, which is connected to the gate of the regulating MOSFET. The drain of the regulating MOSFET is connected to the gate of the power MOSFET, and the source of the regulating MOSFET is grounded. The voltage divider module is a resistive voltage divider module, including a first voltage divider resistor (resistor R2) and a second voltage divider resistor (resistor R6) connected in series. The series connection point of the first voltage divider resistor (resistor R2) and the second voltage divider resistor (resistor R6) is the voltage divider output pin.

[0029] The working principle of the switching circuit in this embodiment is as follows:

[0030] When S1 is closed, the input power supply V1, through resistors R1, R3, TL431 chip U1, R4, and R5, and the voltage reference circuit (i.e., the first regulating circuit) composed of resistors R3, TL431 chip U1, R4, and R5, maintains the gate voltage of the power MOSFET at a fixed voltage. At this time, the V of the MOSFET... GS With a fixed voltage (gate and source voltage), utilizing the characteristics of a MOSFET, when the MOSFET operates in the saturation region, the current I flowing from the source to the drain is... D It is fixed, I D and V GS Relatedly, the capacitor C1 at the back end is slowly charged. When the drain voltage (i.e., the output voltage) of the power MOSFET rises to the set value, which is set by resistors R2 and R6, the MOSFET (Q2) is turned on, allowing the power MOSFET (Q1) to work in the linear region. The power MOSFET (Q1) is used as a switch, which means it can supply power to the back end circuit through a large current.

[0031] The first regulating circuit of this invention is configured as a voltage reference circuit, which causes the power MOSFET to operate in the saturation region, and the gate-source voltage V of the power MOSFET... GS The clamping position is at a low voltage, thus enabling low-current charging. The voltage drop across the equivalent parasitic resistance at the front end of the switch is small, and the voltage drop amplitude of the external power supply pin is small, ensuring reliable power supply to the circuit. The second regulating sub-circuit combines a voltage divider module and a regulating MOSFET. The operating state of the MOSFET is adjusted by the voltage division of the resistor in the voltage divider module. The time for the power MOSFET to enter the linear region can be adjusted according to the circuit operation, making debugging flexible and convenient.

[0032] The above embodiments are merely illustrative and do not constitute a limitation on the scope of the present invention. These embodiments can also be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the technical spirit of the present invention.

Claims

1. A power MOSFET-based switching circuit comprising an input power supply, a switch and a power MOSFET, the power supply being connected to the source of the power MOSFET through the switch, the drain of the power MOSFET being an output terminal and being connected to one end of a capacitor, the other end of the capacitor being connected to ground, the front end of the switch being provided with an external power supply pin, the power MOSFET being a P-type MOSFET, characterized in that, The circuit further comprises: a first regulating sub-circuit, which controls the power MOSFET to work in a saturation region when the switch is closed and the output voltage is lower than a set threshold, and the capacitor is charged with a small current; a second regulating sub-circuit, which controls the power MOSFET to work in a linear region when the switch is closed and the output voltage is greater than the set threshold, and the capacitor is charged with a large current.

2. A power MOSFET-based switching circuit according to claim 1, wherein, The first regulating sub-circuit comprises a voltage reference circuit, an input end of which is connected to the source of the power MOSFET, and an output end of which is connected to the gate of the power MOSFET.

3. A power MOSFET-based switching circuit according to claim 2, wherein, The voltage reference circuit comprises a voltage reference circuit composed of a TL431.

4. A power MOSFET-based switching circuit according to claim 1, wherein, The second regulating sub-circuit comprises a voltage dividing module and a regulating MOSFET, the voltage dividing module is connected in parallel with the capacitor, the voltage dividing module is provided with a voltage dividing output pin, the voltage dividing output pin is connected to the gate of the regulating MOSFET, the drain of the regulating MOSFET is connected to the gate of the power MOSFET, and the source of the regulating MOSFET is grounded.

5. A power MOSFET-based switching circuit according to claim 4, wherein, The voltage dividing module is a resistance voltage dividing module, which comprises a first voltage dividing resistor and a second voltage dividing resistor connected in series, and the series connection point of the first voltage dividing resistor and the second voltage dividing resistor is the voltage dividing output pin.

6. A power MOSFET-based switching circuit according to claim 4, wherein, The regulating MOSFET is an N-type MOSFET.

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