Power semiconductors
When a power MOSFET's gate is charged with a constant current, why does the gate voltage stay flat for a while (the Miller plateau)?
- ABecause the gate current stops
- BBecause the gate insulator temporarily breaks down
- CBecause while the drain voltage is changing, the gate current is used to charge and discharge the gate-drain capacitance
Show answer and explanation
Answer: C. Because while the drain voltage is changing, the gate current is used to charge and discharge the gate-drain capacitance
While the drain voltage swings widely during switching, the current fed into the gate goes into charging or discharging the gate-drain capacitance (Miller capacitance), so the gate voltage stays nearly constant. This flat region is the Miller plateau, and its length strongly affects switching speed and loss.
- A. The gate current keeps flowing.
- B. It is not a breakdown of the insulator.
- C. Correct. The current goes into charging the Miller capacitance.