When designing fast-switching circuits, MOSFET reverse recovery can sneak in as a silent performance killer. If not addressed, it can cause heat buildup, inefficiency, or even damage.

⚠️ The Problem: Reverse Recovery in MOSFETs

MOSFETs are ideal for switching, but in circuits with inductive loads (like motors or transformers), the body diode conducts briefly when the MOSFET turns off. The problem? That diode has reverse recovery time (trr)—the time it takes to stop conducting. This delay can result in power loss and unwanted heat.

🔧 The Solution: Fast Diodes or Synchronous Switching

To fix this, you can:

• Use MOSFETs with fast body diodes or external Schottky diodes.

• Implement synchronous switching using complementary MOSFETs to eliminate body diode conduction.

• Ensure snubbers or gate resistors limit switching spikes.

💡 Practical Example: Switching a Motor Driver

Let’s say you’re using an N-channel MOSFET to switch a 12V DC motor. During fast PWM control, the body diode turns on momentarily. If it has a high trr, the MOSFET heats up.

🔁 Solution: Use an external Schottky diode with low recovery time (e.g., 30ns) in parallel with the MOSFET.

🧮 Sample Calculation: Diode Recovery Loss

Assume:

• trr = 100ns

• Reverse current = 1A

• Switching freq = 50kHz

• Loss = 0.5 × trr × Ir × V × f
  = 0.5 × 100e-9 × 1 × 12 × 50,000
  = 0.03W per cycle.
  Over time, that’s significant!

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