Do you know that the Miller effect of MOS tubes has other uses?

Remember what the Miller effect is?

This is an NMOS switch circuit. Here VG1 sets the DC level to 2V, square wave (amplitude 2V, frequency 50Hz), T2's turn-on voltage is 2V, and the turn-on and turn-off states are performed with a period of T=20ms.

 When Vgs=2V, a small platform will appear, which is the Miller platform we often mention .

 When the resistor R1 in this circuit is changed from 5K to 1K, it is found that the platform becomes smaller.

 why is that?

The Miller effect is mainly due to the existence of Miller capacitance , which is produced by the MOS tube manufacturing process and cannot be avoided.

So what happens during the Miller Effect? Why does it happen?

This is related to the working principle of MOS tube.

We have previously mentioned that the activation of a MOS tube can be divided into four stages (Series: Understanding MOSFET from 0 to 1).

 Generally, the Miller platform appears in Vgs during the t2~t3 stage:

When the Vgs voltage rises, the IDS current is the same as the inductor current, the D-pole voltage of the MOS tube is no longer clamped by the diode DF, DF is in reverse cutoff, and Vds begins to decrease.

At this time, the G-pole driving current is transferred to Cgd for charging, and a Miller platform appears on Vgs. The VGs voltage remains unchanged, and Vds gradually decreases to the on-state voltage drop VF.

 t2~t3 equivalent circuit

The Miller platform will increase the conduction time of the MOS tube, which is what we often call conduction loss.

Usually we will increase the driving voltage or reduce the driving resistance to reduce the Miller effect of the MOS tube, in order to increase the driving current and charge quickly.

However, the emergence of the Miller platform is not without merit.

It is still very useful in power supply slow start.

Since the voltage Vds across the MOS tube drops, the MOS tube can be used as a switch to slow-start the power supply, power independent modules, and power on high-power equipment, which are all very useful.

Some of the above pictures and information are from the Internet