Do you know the MOSFET driver circuit？

The MOSFET driver circuit is a crucial part of power electronics and circuit design, which is responsible for providing sufficient drive capability to ensure that the MOSFET can work properly and reliably. The following is a detailed analysis of MOSFET driver circuits:

I. Role of the drive circuit

Provide sufficient drive capacity:Since the drive signal is often given from a controller (e.g. DSP, microcontroller), the drive voltage and current may not be sufficient to directly turn the MOSFET on, so a drive circuit is required to match the drive capability.

Ensure good switching conditions:The driver circuit needs to ensure that the MOSFETs are neither too fast nor too slow during switching to avoid EMI problems and excessive switching losses.

Ensure the reliability of the device:Due to the presence of parasitic parameters of the switching device, voltage-current spikes may be generated during conduction or turn-off, and the driver circuit needs to suppress these spikes to protect the circuit and the device.

II. Types of drive circuits

 

Non-isolated driver

Direct Drive:The simplest way to drive the MOSFET is to connect the drive signal directly to the gate of the MOSFET. This method is suitable for occasions where the driving capability is sufficient and the isolation requirement is not high.

Bootstrap Circuit:Using the principle that the capacitor voltage cannot be changed abruptly, the voltage is automatically lifted when the MOSFET changes its switching state, thus driving the high-voltage MOSFET.This approach is commonly used in cases where the MOSFET cannot share a common ground with the driver IC, such as BUCK circuits.

Isolated Driver

Optocoupler isolation:The isolation of the drive signal from the main circuit is achieved through optocouplers. Optocoupler has the advantages of electrical isolation and strong anti-interference ability, but the frequency response may be limited, and the life and reliability may be reduced under harsh conditions.

Transformer isolation:The use of transformers to achieve the isolation of the drive signal from the main circuit. Transformer isolation has the advantages of good high-frequency response, high isolation voltage, etc., but the design is relatively complex and susceptible to parasitic parameters.

Third, the design of the driving circuit points

Drive Voltage:It should be ensured that the drive voltage is higher than the threshold voltage of the MOSFET to ensure that the MOSFET can conduct reliably. At the same time, the drive voltage should not be too high to avoid damaging the MOSFET.

Drive current:Although MOSFETs are voltage-driven devices and do not require much continuous drive current, the peak current needs to be guaranteed in order to ensure a certain switching speed. Therefore, the driver circuit should be able to provide sufficient peak current.

Drive Resistor:The drive resistor is used to control the switching speed and suppress current spikes. The selection of the resistor value should be based on the specific circuit and the characteristics of the MOSFET. In general, the resistor value should not be too large or too small to avoid affecting the driving effect and circuit performance.

PCB Layout:During PCB layout, the length of the alignment between the driver circuit and the MOSFET gate should be shortened as much as possible, and the width of the alignment should be increased to reduce the impact of parasitic inductance and resistance on the driving effect. At the same time, key components such as drive resistors should be placed closer to the MOSFET gate.

IV. Examples of applications

MOSFET driver circuits are widely used in a variety of power electronic devices and circuits, such as switching power supplies, inverters, and motor drives. In these applications, the design and optimisation of the driver circuits are critical to improve the performance and reliability of the devices.

In summary, MOSFET driving circuit is an indispensable part of power electronics and circuit design. By reasonably designing the driver circuit, it can ensure that the MOSFET works normally and reliably, thus improving the performance and reliability of the whole circuit.