Martin McCormick wrote:
>
>         How about using a RC filter as several have suggested but feeding the
> variable DC voltage in to the + input of just about any garden variety op
> amp such as a 741 whose gain  is set to provide an output voltage range
> from 0 to 13 volts with a 0-5 volt input.  The op amp's low-impedance output
> would drive either a source follower or emitter follower circuit which would
> be what actually supplied power to the fan motor.  The only problem is what
> to do with the op amp's power supply.  If there is a duel-ended 15-volt
 supply,
> it is almost trivial as long as one does not mind that the negative half
> of the operational amplifier's range is never used.  The op amp can be used
> with a single-ended supply by providing it with a fake ground at half the
> supply voltage.  I would rather have the duel-ended supply up front than
> to have to mess with the resistive divider net on each amplifier, but that's
> just my opinion and worth just what you paid for it.
>
> Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
> OSU Center for Computing and Information Services Data Communications Group
I to wondered why a power op_amp could not be used with an r/c
integrator
on the non inverting input "high impedance" and a voltage divider for
the
inverting input or even just a darlington instead of the op_amp . No
feedback was
mentioned "I think" so have fun. Tony M.