MOSFET Switching Speed Tips
🔍 The Problem :
When MOSFETs switch too slowly, they generate excess heat, reduce efficiency, and can even damage your circuit. This is a common issue in high-speed switching applications like motor drivers and DC-DC converters. The culprit? Often it’s poor gate drive or incorrect resistor values.
🛠 The Solution :
To speed up switching, use a gate driver IC and optimize the gate resistor. A low-value resistor (10Ω–100Ω) balances fast switching and safe EMI levels. Choosing a MOSFET with low gate charge (Qg) also helps.
💡 Practical Example :
Let’s say you’re building a BLDC motor controller.
Your N-channel MOSFET has a total gate charge of 25nC and is driven by a 12V gate driver.
To switch it in 100ns:
Current = Q / t = 25nC / 100ns = 0.25A
Using Ohm’s Law,
R = V / I = 12V / 0.25A = 48Ω
A 47Ω gate resistor would be ideal for clean, fast switching.
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