An NMOS high-side drive circuit

Abstract

The present invention relates to an NMOS high-side drive circuit, in particular to an NMOS high-side drive circuit containing a microcontroller and used for controlling the on / off of a DC power supply. It includes a microcontroller circuit, an opto-isolation circuit, a boost drive circuit, an NMOS transistor, an auxiliary power supply circuit, a controlled DC power supply, and a controlled load or electrical device. In this control, the NMOS transistor is equivalent to a power switch. The saturation conduction of the NMOS transistor is equivalent to the closing of the switch, and the cutoff of the NMOS transistor is equivalent to the opening of the switch. Generally, for the NMOS transistor to be saturated and conducting, the gate potential needs to be 4V or even more than 10V higher than the source potential. The prior art generally requires the use of a dedicated drive chip or a boost transformer to provide this drive voltage. The present invention uses the microcontroller and common low-cost components such as resistors and capacitors contained in the system itself to generate the drive voltage required for NMOS high-side drive. This NMOS high-side drive circuit has the characteristics of simple circuit and easy implementation, can reduce the complexity of circuit design, and improve the cost performance of the product.

Description

Technical Field

[0001] The present invention relates to an NMOS high-side drive circuit, and particularly to an NMOS high-side drive circuit for controlling the on / off of a DC power supply containing a microcontroller. Background Art

[0002] In an electronic device containing a microcontroller, it is often necessary to control the on / off of the DC power supply for the controlled system through key operations. To achieve the on / off control of the DC power supply for the controlled system, a circuit structure in which the drain of an NMOS transistor is connected to the power supply and the source is connected to the power supply terminal of the controlled system is often used, that is, the so-called NMOS high-side drive circuit. In this control, the NMOS transistor is equivalent to a power switch. The saturation conduction of the NMOS transistor is equivalent to the closing of the switch, and the cutoff of the NMOS transistor is equivalent to the opening of the switch. Generally, the gate potential needs to be 4V or even more than 10V higher than the source potential for the NMOS transistor to be saturated and conducting. In the NMOS high-side drive circuit, the saturation conduction of the NMOS transistor is equivalent to the source voltage being equal to the drain voltage being equal to the power supply voltage. Therefore, the NMOS high-side drive requires a DC drive voltage higher than the controlled power supply voltage by 4V or even more than 10V. In this on / off control of the DC power supply, the NMOS transistor needs to maintain a saturated conduction state for a long time. During this period, its gate voltage needs to be kept higher than the controlled power supply voltage by 4V or even more than 10V. Therefore, the method of capacitor bootstrap boosting cannot be used to provide this drive voltage. The DC drive voltage of the existing NMOS high-side drive circuit for the on / off control of the system DC power supply mostly uses a dedicated NMOS high-side drive integrated circuit or is generated by using a step-up transformer. The existing technical solutions increase the complexity of the circuit design and improve the system design cost. Summary of the Invention

[0003] The object of the present invention is to generate a drive voltage higher than the power supply voltage of the controlled system by 4V or even more than 10V required for NMOS high-side drive by using the microcontroller and common low-cost components contained in the electronic device itself, in order to reduce the complexity of the circuit design and improve the cost performance of the product.

[0004] The technical solution adopted to achieve the object of the present invention is:

[0005] An NMOS high-side drive circuit includes a microcontroller circuit, an opto-isolation circuit, a boost drive circuit, an NMOS transistor, an auxiliary power supply circuit, a controlled DC power supply, and a controlled load or electrical device. The microcontroller circuit, the boost drive circuit input, the auxiliary power supply circuit, the controlled DC power supply, and the controlled load or electrical device are isolated by the opto-isolation circuit. The microcontroller circuit generates a square wave of a certain frequency, and this square wave is sent to the boost drive circuit through the opto-isolation circuit for rectification and boosting. The output terminals of the boost drive circuit are "floating ground". The two output terminals of the boost drive circuit are directly connected to the gate and source of the NMOS transistor as the drive voltage of the NMOS transistor. The drain of the NMOS transistor is connected to the controlled DC power supply, and the source of the NMOS transistor is connected to the positive terminal of the DC power supply of the controlled load or electrical device. The auxiliary power supply circuit provides power for the boost drive circuit, and the input of the auxiliary power supply circuit is provided by the controlled DC power supply.

[0006] The beneficial effects of the present invention are as follows: By using the microcontroller of the electronic device itself and low-cost resistor and capacitor components, a high voltage required for NMOS high-side drive is provided, simplifying the circuit design and improving the cost performance of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG Figure 1 is the circuit schematic diagram of an NMOS high-side drive circuit of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0008] To better understand the present invention, the embodiments will be described in detail below with reference to the drawings.

[0009] An NMOS high-side drive circuit includes a microcontroller circuit, an opto-isolation circuit, a boost drive circuit, an NMOS transistor, an auxiliary power supply circuit, a controlled DC power supply, and a controlled load or electrical device.

[0010] As shown in the drawings, in this embodiment, the controlled DC power supply VDD is 24V. The auxiliary power supply circuit consists of a three-terminal voltage regulator IC3, input filter capacitors C3 and C4, and output filter capacitors C1 and C2, where the three-terminal voltage regulator is LM7809. The 9V output of the auxiliary power supply circuit supplies power to the boost drive circuit. The working principle is as follows:

[0011] The microcontroller IC1 in the microcontroller circuit generates a square wave output when the NMOS transistor needs to be turned on, and stops the square wave output and makes the pin that generates the square wave output output a low level when the NMOS transistor needs to be turned off.

[0012] Further, the square wave generated by the microcontroller is converted into a square wave with an amplitude equal to the output voltage of the auxiliary power supply circuit after passing through the opto-isolation circuit, and then this square wave is fed into the input end of the boost driving circuit. The opto-isolation circuit includes resistor R1, triode Q1, optocoupler IC2, resistor R2, and resistor R3. Among them, one end of the current-limiting resistor R1 output by the microcontroller is connected to the I / O pin of the microcontroller, and the other end is connected to the base of the NPN-type triode Q1. The emitter of the NPN-type triode Q1 is connected to the power ground of the microcontroller circuit, and the collector is connected to the cathode of the light-emitting diode at the input end of the optocoupler. The anode of the light-emitting diode at the input end of the optocoupler is connected to one end of the current-limiting resistor R2, and the other end of the current-limiting resistor R2 is connected to the positive pole of the power supply for the microcontroller. The emitter of the transistor at the output end of the optocoupler is connected to the negative ground terminal of the controlled DC power supply. The collector of the transistor at the output end of the optocoupler is connected to one end of the load resistor R3 and the input end of the boost driving circuit. The other end of the load resistor R3 is connected to the positive terminal of the auxiliary power supply output.

[0013] Further, the boost driving circuit includes four diodes D1~D4 and five non-polar capacitors C5~C9. Among them, one end of capacitor C5 and one end of capacitor C6 are connected together as one input end of the boost driving circuit. The other input end of the boost driving circuit is connected to the negative ground terminal of the controlled DC power supply. The other end of capacitor C5, the cathode of diode D1, and the anode of diode D2 are connected together. One end of capacitor C7, the cathode of diode D2, and the anode of diode D3 are connected together. The other end of capacitor C6, the cathode of diode D3, and the anode of diode D4 are connected together. The anode of diode D1, the other end of capacitor C7, one end of capacitor C8, and one end of capacitor C9 are connected together as the negative output end of the boost driving circuit and connected to the source of the NMOS transistor. The other end of capacitor C9 is connected to the negative ground terminal of the controlled DC power supply. The other end of capacitor C8 and the cathode of diode D4 are connected together as the positive output end of the boost driving circuit and connected to the gate of the NMOS transistor. It should be particularly noted that the output of the above-mentioned boost driving circuit is taken from both ends of capacitor C8 and is "floating ground", directly connected between the gate and the source of the NMOS transistor.

[0014] Further, a discharge resistor R4 with a resistance value of 100 kΩ is connected between the gate and the source of the NMOS transistor to achieve rapid turn-off of the NMOS transistor.

[0015] Further, the controlled load or electrical device is connected between the source of the NMOS transistor and the negative ground terminal of the controlled DC power supply.

[0016] In this embodiment, the auxiliary power supply circuit can ensure that the voltage output by the boost drive circuit can saturate and turn on the NMOS transistor without damaging the NMOS transistor; the opto-isolation circuit can prevent high voltage from damaging the microcontroller and at the same time improve the anti-interference ability of the microcontroller.

[0017] The above implementation manner is only a preferred implementation manner of the present invention, and any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. An NMOS high-side drive circuit, comprising a microcontroller circuit, an opto-isolation circuit, a boost drive circuit, an NMOS transistor, an auxiliary power supply circuit, a controlled DC power supply, and a controlled load or electrical device; Characterized in that: The microcontroller circuit, the boost drive circuit, the auxiliary power supply circuit, the controlled DC power supply, and the controlled load or electrical device each use two independent power supplies, which are isolated through the opto-isolation circuit. The microcontroller circuit generates a square wave with a certain frequency, and this square wave is sent to the boost drive circuit through the opto-isolation circuit for rectification and boosting. One end of the capacitor C8 in the boost drive circuit is connected to the source electrode of the NMOS transistor, and the other end of the capacitor C8 is connected to the gate electrode of the NMOS transistor, serving as the drive voltage for the gate and source electrodes of the NMOS transistor. The drain electrode of the NMOS transistor is connected to the controlled DC power supply, the source electrode of the NMOS transistor is connected to the positive polarity end of the power supply of the controlled load or electrical device, the input of the auxiliary power supply circuit is provided by the controlled DC power supply, and the auxiliary power supply circuit provides power for the boost drive circuit.

2. The NMOS high-side drive circuit according to claim 1, Characterized in that: The microcontroller circuit includes a microcontroller.

3. The NMOS high-side drive circuit according to claim 1, Characterized in that: The microcontroller circuit can generate a square wave above 1 KHz.

4. The NMOS high-side drive circuit according to claim 1, Characterized in that: The microcontroller circuit generates a square wave output when the NMOS transistor needs to be turned on, and stops the square wave output when the NMOS transistor needs to be turned off.

5. The NMOS high-side drive circuit according to claim 1, Characterized in that: The microcontroller circuit outputs a low level when the NMOS transistor needs to be turned off.

6. The NMOS high-side drive circuit according to claim 1, Characterized in that: The opto-isolation circuit includes a microcontroller output current-limiting resistor R1, an NPN-type triode Q1, an opto-coupler IC2, a current-limiting resistor R2 at the input end of the opto-coupler, and a load resistor R3 at the output end of the opto-coupler; wherein, one end of the microcontroller output current-limiting resistor R1 is connected to an I / O pin of the microcontroller, and the other end is connected to the base of the NPN-type triode Q1. The emitter of the NPN-type triode Q1 is connected to the power ground of the microcontroller, and the collector is connected to the cathode end of the light-emitting diode at the input end of the opto-coupler. The anode end of the light-emitting diode at the input end of the opto-coupler is connected to one end of the current-limiting resistor R2, and the other end of the current-limiting resistor R2 is connected to the positive pole of the power supply for the microcontroller. The emitter of the transistor at the output end of the opto-coupler is connected to the negative ground end of the controlled DC power supply, the collector of the transistor at the output end of the opto-coupler is connected to one end of the load resistor R3 and the input end of the boost drive circuit, and the other end of the load resistor R3 is connected to the positive output end of the auxiliary power supply.

7. The NMOS high-side drive circuit according to claim 1, Characterized in that: The boost driving circuit includes four diodes D1 to D4 and five non-polar capacitors C5 to C9. Among them, one end of capacitor C5 and one end of capacitor C6 are connected together as an input terminal of the boost driving circuit, and the other input terminal of the boost driving circuit is connected to the negative ground terminal of the controlled DC power supply. The other end of capacitor C5, the cathode of diode D1, and the anode of diode D2 are connected together. One end of capacitor C7, the cathode of diode D2, and the anode of diode D3 are connected together. The other end of capacitor C6, the cathode of diode D3, and the anode of diode D4 are connected together. The anode of diode D1, the other end of capacitor C7, one end of capacitor C8, and one end of capacitor C9 are connected together as the negative output terminal of the boost driving circuit and connected to the source of the NMOS transistor. The other end of capacitor C9 is connected to the negative ground terminal of the controlled DC power supply. The other end of capacitor C8 and the cathode of diode D4 are connected together as the positive output terminal of the boost driving circuit and connected to the gate of the NMOS transistor.

8. The NMOS high-side driving circuit according to claim 1, characterized in that: the output of the boost driving circuit is taken from both ends of capacitor C8.

9. The NMOS high-side driving circuit according to claim 1, characterized in that: a 100 kΩ resistor R4 is connected between the gate and the source of the NMOS transistor.

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