🔍 Key Concepts

• MOSFET gate characteristics vs. bipolar transistor base characteristics • What input impedance at the control terminal (gate/base) means for the driving circuit in a switching power supply • Typical failure modes of MOSFETs when subjected to excessive voltage or heat

💭 Think About

• Think about whether a MOSFET gate draws significant current in normal operation. Would that make its input impedance high or low? • Compare MOSFETs to bipolar junction transistors: which one is associated more with thermal runaway, and which with voltage breakdown at the control terminal? • In a high‑frequency RADAR switching supply, would you prefer a device that is easy to drive with low current or one that needs substantial drive current?

✅ Before You Answer

• Verify whether a MOSFET gate behaves more like a capacitive, high‑impedance input or a resistive, low‑impedance input. • Check which failure term, gate punch-through / gate breakdown vs. thermal runaway, is more commonly associated with voltage damage to the MOSFET gate oxide. • Confirm that in a switching supply, designers typically want high input impedance at the control terminal to simplify the drive circuitry.