Just had a design requirement changed by factors outside my control.
A FET which previously has a nominal 15 volt gate drive voltage supplied
from an
AC source and a voltage doubler now has only a guaranteed 6 to 9 volt source
available. Volume production mandates lowest possible cost (and it's fun in
any case to see how low you can go).

Suggestions are sought for an elegant (ie cheap :-) )  FET gate drive power
supply circuit capable of
generating +15 volts  from an input of as little as 5 volts.
No problem doing this of course but someone may have a good suggestion.

The main design requirements are
    must work,
    LOW COST,
    low parts count.
    low cost
    low cost

Drive requirement is a few mA average (2000 pF gate capacitance, 15 volts,
20 kHz)
Output voltage tolerance is loose (12 - 15v ish, zener regulation fine).

Possible solutions include

- Capacitor pump (would need to be a tripler, not just a doubler. Could use
IC (766x etc) or discrete using drive signal from processor. Separate IC
seems unnecessarily complex.

- Small flyback converter (one transistor, 2 winding inductor, diode, not
too much else).

- Flyback or boost converter using processor drive signal (one transistor,
choke, diode not too much else)

- With a PIC (not available) an inductor on  pin A4 (open collector) would
give the ultimate minimum parts count :-) (inductor, diode)

Zener clamp regulation assumed in all cases due to absolutely minimal power
level.

- Off shelf package 50 mW  :-) converter - too dear.

Any other clever ideas?


Russell McMahon

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