On Tue, 19 Nov 2002, Roman Black wrote:

> WH Tan wrote:
> >
> > I wish to control a 13V dc supply with a digital logic high 5V. How to
> > achieve this purpose by using a general purpose transistor?
>
>
> One PNP transistor, (high side) and 3 resistors.
> Connect the resistors as a 3 section voltage
> divider so that when digital pin is at 5v the
> voltage across B-E is only about 0.4v. When the
> digital pin goes low the voltage B-E rises to
> about 0.8v and PNP turns on. :o)
> -Roman
>
  Nice, but not recomandable for high curents through PNP.
  Old fashion: a npn transistor or an open collector gate with 15V Vce (
unfortunately the open drain ra4 style is out of voltage spec ) which
control a power NPN ( darlinghton if necessary ). A resistor across the BC
of power transistor keep the transistor on, the open colector controlling the
base of the same transistor shut down the whole kk when is on.
Everything can be replaced with a 4 terminal controlled 12V stab with
reference adjustment floated with 1V upper the ground using a
simple resistor.

Eagle users on the list ?

by, Vasile

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