MOS tube G pole protection problem

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MOS tube G pole protection problem [Copy link]

The picture above is a half bridge. What are the functions of Cg1/Cg2 and Rg2/Rg4? I searched on Baidu and it says that the capacitor is used to accelerate the opening, and the resistor is used to accelerate the release of the charge between GS.

I don't quite understand, so I'll analyze and explain @ maychang @ chunyang

maychang

The function of Cg1 and Cg2 is indeed to accelerate the opening of the MOS tube.

The effect of resistors Rg2 and Rg4 in "accelerating the release of charge between GS" is very small and can be almost ignored. Whether there is an effect of "accelerating the release of charge between GS" depends on the values of RG2 and Rg4. If the values of Rg2 and Rg4 are several ohms, and the product of them and the gate input capacitance of the MOS tube (including Miller capacitance) (i.e. the time constant of the RC circuit) is much smaller than the PWM cycle, then these two resistors can indeed "accelerate the release of charge between GS". However, with such a small resistance, the front stage is simply unable to drive, and the circuit cannot work. If Rg2 and Rg4 reach thousands of ohms, there is no effect of "accelerating the release of charge between GS" at all, because in this case, the RC time constant is greater than the PWM cycle.

maychang

When Rg3, Rg1, etc. have not been soldered but Rg2 and Rg4 have been soldered to the circuit board, it can protect the gate of the MOS tube.

The gate of the MOS tube has a high impedance to the source and a relatively low withstand voltage, and is easily broken down by static electricity, especially when soldering to the circuit board. If Rg2 and Rg4 have been soldered to the circuit board before soldering the MOS tube, a low impedance path to the ground can be provided for the gate, and the possibility of the gate being broken down during soldering is much smaller than when there are no Rg2 and Rg4.

chunyang

Cg is the turn-on acceleration capacitor, and Dg is the turn-off acceleration. Rg is the static bias, and also has the gate protection function mentioned by maychang above.

se7ens

Very good MOSFET drive circuit and analysis, thanks for sharing

寅子敬

Does this type of drive with two enhancement-mode NMOS connected in series have a name? How is it analyzed?

S3S4S5S6

Yin Zijing posted on 2021-3-23 18:09 Does this type of drive that connects two enhanced NMOSs in series have a name? And how is it analyzed?

This is a half-bridge driven by a stepper motor, only half of the circuit is shown