The Problem :

When switching a MOSFET at high speed, the internal Miller capacitance (Cgd) can cause unwanted gate voltage spikes. This may result in false turn-on, excessive heat, or switching noise—especially in power supplies and motor drivers.

The Solution :

To prevent this, we use a gate resistor and a Miller clamp or snubber circuit. These limit the gate’s rate of voltage change (dV/dt) and suppress false triggering caused by the Miller effect. For critical designs, opt for MOSFET drivers with built-in Miller suppression.

Practical Example :

If you’re prototyping a DC motor controller and notice the motor turning on erratically, the Miller effect is likely at play. Adding a 10Ω gate resistor and selecting a MOSFET with low Cgd will help stabilize switching behavior.

Sample Calculation :

Assume Cgd = 200pF, Vds change = 15V, and switching time = 100ns:

Current injected into gate = Cgd × (dV/dt) = 200e-12 × (15/100e-9) = 30mA

This surge could falsely turn on the gate without proper resistance.

Product Recommendation :

Use quality Made in India components:

• MOSFETs

• [Gate Resistors]

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