Regulating gate/base voltage.

[mael]

I want to drive power transistors/MOSFETS using discrete components.

The way I see it is that one uses a driver transistor - that's easy enough. But how does one get the voltage stabilised?

Zeners? Amplified zeners? K! (In the case of an NPN) would I connect a zener with its band (pos) to the base and the minus to earth along with the emitter and .......... well can someone sort me out?

Once I get the hang of it I'll be OK to advance on my own. But I'm not sure how to use zeners/amplified zeners and I want to use them in a pulser for reviving lead/acid batteries.

Please teach me how to make such a circuit. Sorry if it is so simple. I've got (half) the gist of it from reading sites on the 'net, but I'd like it explained in baby-talk. - Well not literally.

[SeaMonkey]

To stabilize the voltage of the power source used for the driver circuits you may use either one of the 3-terminal regulators (i.e. 7815) or a single transistor configured as an Emitter Follower. This stabilized power source may be derived from the unregulated source that will be used to provide the 'power pulses' to the battery being rejuvenated. This supply should be able to provide a current up to 1 or 2 Amperes briefly to the driver circuits.

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?

[mael]

[SeaMonkey]

[SeaMonkey]