At 04:22 AM 2/1/02 +1000, you wrote:

>So what you need is some simple way to switch off the regulator and
>have its o/p volts go to zero when it's OFF = when the npn tarnsistor
>is OFF.

A P-channel logic MOSFET, a resistor, and an open-collector driver
(2N4401 + a resistor), in series with the input of the regulator.
+a zener and another resistor if the 12V might have transients that
could kill the 20V MOSFET gate. Or use a PNP 'tarnsistor' instead of
the MOSFET.

But, really, it would be better to just use an LM2941 (in TO-220-5
or TO-263-5) that has shutdown built-in, is LDO and costs about 85
cents in 100's (adjustable output voltage).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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