Understanding MOSFET Reverse Recovery Time :

When working with MOSFETs in electronic circuits, one common issue you might encounter is reverse recovery time. This is the brief delay that occurs when a MOSFET switches from conducting to non-conducting mode (or vice versa). Essentially, when the MOSFET turns off, it doesn’t stop conducting immediately; instead, it takes a short moment to recover. This delay can cause inefficiencies, overheating, or even damage in high-speed circuits.

The Problem :

The best way to minimize reverse recovery time is by choosing MOSFETs with fast recovery characteristics or using a diode in parallel to prevent unwanted current spikes. This can be especially useful when working with power supplies or switching circuits.

Example :

Imagine you’re designing a power supply circuit for a hobby project. You’ve chosen a MOSFET for switching, but your circuit behaves erratically. After some testing, you find that reverse recovery time is the culprit, causing current spikes when switching off. To fix this, you replace the MOSFET with one that has a lower reverse recovery time or add a fast diode in parallel to absorb the spikes.

Sample Calculation :

Let’s say your MOSFET has a reverse recovery time of 200ns, and you’re switching at 1 MHz.

The amount of time the MOSFET stays “on” unnecessarily can be calculated by multiplying the switching frequency (1 MHz) by the recovery time (200ns).

Excess Time = Switching Frequency × Reverse Recovery Time

Substituting the values:

Excess Time = (1 MHz) × (200 ns)

Since 1 MHz = 1,000,000 Hz and 200 ns = 200 × 10⁻⁹ seconds, we get:

Excess Time = (1,000,000) × (200 × 10⁻⁹)

Excess Time = 0.0000002 seconds

That’s a tiny delay, but in high-speed circuits, it can lead to power loss or even component stress.

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