1. ECE 2799 Electrical and Computer Engineering Design “POWER SWITCHING TECHNIQUES” Prof. Bitar

2. Copyright - Stephen J. Bitar 2006 Power Switching Devices Manual Switch Manual Switch Electro-Mechanical Relay Electro-Mechanical Relay Bipolar Junction Transistor (BJT) Bipolar Junction Transistor (BJT) Darlington Pair (BJT) Darlington Pair (BJT) Power MOSFET Power MOSFET

3. Copyright - Stephen J. Bitar 2006 Manual Switch Pro’s Pro’s Simple Con’s Con’s Control Current = Load Current Heavy Gauge Wire Required Throughout

4. Copyright - Stephen J. Bitar 2006 Electro-Mechanical Relay Pro’s Pro’s Control Current Less Than Load Current Independent Sources No Heatsink Required Con’s Con’s Control Current (100- 200mA typical) Limited Switching Speed Inductive Spikes Produces Electro-Magnetic Interference (EMI)

5. Copyright - Stephen J. Bitar 2006 Bipolar Junction Transistor (BJT) Pro’s Pro’s Control Current Less than Load Current Independent Sources (BUT requires common ground) Fast Switching Speeds Con’s Con’s Requires Resistance to Limit Base Current May Require Substantial Base Current Power Device has low β (25 Typical) May Require Heatsink

6. Copyright - Stephen J. Bitar 2006 Darlington Pair (w/ BJT’s) Pro’s Pro’s High β (1000 Typical) Control Current MUCH Less than Load Current Independent Sources (BUT requires common ground) Fast Switching Speeds Con’s Con’s V CE Saturation ~ 1V May Require Heatsink

7. Copyright - Stephen J. Bitar 2006 Power MOSFET Pro’s Pro’s I GATE (DC) = 0 ! Easy to Drive Independent Sources (BUT requires common ground) Fast Switching Speeds Con’s Con’s Requires Large V GS Susceptible to ESD Damage May Require Heatsink