..................................................2 1. Driving a MOSFET ...........................................................................................................................3 1.1. Gate drive vs. base drive.................................................................................................................... 3 1.2. MOSFET characteristics ...................................................................................................................... 3 1.2.1. Gate charge ...........................................................................................................................................4 1.2.2. Calculating MOSFET gate charge .......................................................................................................4 1.2.3. Gate charging mechanism...................................................................................................................5 1.3. Gate drive power ................................................................................................................................. 6 2. Example of a MOSFET gate drive circuit ......................................................................................8 2.1. Basic drive circuit................................................................................................................................. 8 2.2. Logic drive............................................................................................................................................. 8 2.3. Drive voltage conversion.................................................................................................................... 9 2.4. High-side drive from a half or full bridge ...................................................................................... 10 2.4.1. Using a high-voltage device and a bootstrap circuit (e.g., high-voltage IC) ............................10 2.4.2. Pulse transformer drive (insulated switching) ...............................................................................10 2.4.3. Using a photocoupler and a floating power supply.......................................................................11 3. Power supply for the MOSFET drive circuit................................................................................12 3.1. Transformer-isolated power supply................................................................................................ 12 3.2. Bootstrap circuit................................................................................................................................. 12 3.3. Charge pump...................................................................................................................................... 13 4. Considerations for the MOSFET drive circuit....................................................................................14 4.1. Considerations for the gate voltage VGS conditions............................................................................. 14 4.2. Gate voltage, peak current and drive loss .................................................................................... 15 4.3. Gate resistors and switching characteristics................................................................................. 15 4.4. Considerations for gate drive .......................................................................................................... 17 4.4.1. Protection against gate-emitter surge voltage ..............................................................................17 4.4.2. Optimal gate resistor..........................................................................................................................17 4.4.3. Gate malfunction prevention ............................................................................................................18 RESTRICTIONS ON PRODUCT USE..........