To drive a Bi-Polar Power Transistor a circuit is configured to provide Base Current sufficient to drive the Power Transistor into 'forward bias' saturation when it is turned 'ON' and a brief pulse of reverse bias to turn it 'OFF' as rapidly as possible. A Darlington Transistor may also be used to reduce driver current requirements and although it will not turn off as rapidly as a single transistor, it will be more than adequate at a pulse frequency below 2 KHz. It is important that the base current to the Power Transistor be only sufficient to drive it into 'hard saturation' and no more; higher levels of base current will result in excessive 'charge storage' in the base region which causes a slow turn-off time.
Power Transistors dissipate most power (heat) during the intervals when they're transitioning from 'cut-off to saturation' and 'saturation to cut-off'; little power is dissipated when the transistor is in saturation where current is maximum.
Most bi-polar power transistors, single or darlington, are able to deliver brief pulses several times greater than their continuous current rating when adequately heat-sinked.
Driving Power MosFets is an easier proposition in that the circuit is simpler in its configuration. It must be able to provide a current pulse of up to 2 Amperes for approximately 3 nanoseconds while charging the MosFet input capacitance to from 10 to 15 Volts in order to turn it fully 'ON'; then to discharge the Gate capacitance within 3 nanoseconds or thereabouts to turn it 'OFF' as rapidly as possible.
The Pulse Generator circuit is a simple 2 transistor RC controlled astable configuration which will be able to produce pulses from 100 Hz to 1 KHz at pulse widths in the range of 1 to 3 milliseconds.
I'll upload some circuit diagrams into the SeaMonkey project folder when they're complete.
Any other questions while we're at it?
You'll find that it's not really too complicated and difficult. Do you have a good supply of diodes, transistors, resistors and capacitors?Statistics: Posted by SeaMonkey — Sun Jan 18, 2009 2:46 am
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