In some low-power switching power supplies, the MOS tubes often use the driving circuit shown in Figure 1.

Figure 1

In this circuit, D represents the charging diode and Q represents the discharging transistor (PNP type).

Its working process is as follows: when the excitation square wave is in the positive half cycle, the charging diode D is turned on and starts to charge the equivalent capacitance at the input end of the MOS tube. At this time, the discharge transistor Q is in the cut-off state;

When the excitation square wave is in the negative half cycle, the charging diode D is cut off, the discharging transistor Q is turned on, and the charge charged by the MOS tube gate S is discharged through Q, thereby enabling the MOS tube to realize the "on" and "off" operations. This process is shown in Figure 2.

Figure 2

This circuit is directly "irrigated" by the excitation signal, so the internal resistance of the excitation signal source is required to be low. It is usually used in low-power switching power supplies.

That’s all for today.