In the circuit, there are three MOS tube junction capacitors, and the parasitic inductance comes from the circuit routing. If factors such as ripple, EMI (electromagnetic interference) and inrush current are not considered, theoretically, the faster the switching speed of the MOS tube, the more beneficial it is to the circuit performance. This is because the shorter the switching time, the smaller the switching loss, and in the switching power supply, the switching loss accounts for a considerable proportion of the total loss. Therefore, the design quality of the MOS tube drive circuit directly determines the efficiency performance of the power supply.

So how to achieve fast opening and closing of MOS tubes?

The key is to provide a sufficiently large instantaneous drive current. The theoretical basis is:

For a single MOS tube, the shorter the time it takes to pull the GS voltage from 0 to the turn-on voltage or from the turn-on voltage to 0V, the faster the turn-on and turn-off speeds. Therefore, to change the GS voltage in a shorter time, a larger instantaneous drive current is required for the gate.

When designing MOS drive circuits, the following points should also be noted:

 A resistor of about 10 ohms is connected in series with the gate to reduce the Q value of the LC oscillation circuit and make the oscillation decay quickly.

In order to prevent the MOS tube from being mis-conducted, a 10K resistor can be connected in parallel between the G and S poles of the MOS tube to reduce the input impedance.

In addition, a TVS transient suppression diode of about 18V is connected in parallel between GS to prevent the MOS tube from being broken down by instantaneous high voltage.