Re: 7824

Thanks for the help, I tested the circuit last night and everything
seems to be working well.

Al

hansw wrote:

>
> From: hansw <hansw@...>
>
> Al,
> That should be OK, the 7812 and 7824 can operate but will not "regulate"
> when the voltage drops below Vreg+3 .
> As the load is is simply a FAN there will be not large capacitors
> storing a charge and you will be OK.
> If however the circuit that is fed by these regulators ( some
> electronics ) an that circuit has large capacitors it is customary to
> connect a diode across the regulator for give a discharge path for such
> stored energy.
> In practice your "circuitry" will discharge such stored energy and you
> can forget about the reverse diode.
>
> Cathode Anode
> |-------|<|-----------|
> Unreg V+----|--------regulator--|----load
>
> In all my years I have not had a single failure of a 7812 or 7824 that
> could be proven to be as a result of this scenario, What people tend to
> do is forget these regulator require a decoupling at the input and
> output, and you can find 7812 that are oscillating in the high MHz band
> because decoupling was left off..
>
> regards
> Hans Wedemeyer
>
> Al Schoepp wrote:
>
> > Hope somebody here can help with an electronics question. I need to
> > step down 30vdc to 12vdc and 24 vdc for a the stepper driver I'm
> > working
> > on. I believe a 7812 and a 7824 chip will work for me. However the
> > specs say that Vin must exceed Vout by 3 volts. When the system is
> > operating that is not a problem. When I turn it off it will take a
> > while for the power supply cap to drop to 0 so at some point in time
> > Vin
> > won't exceed Vout by 3v. Will this damage anything? If so how do I
> > prevent this from happening. The stepped down voltage will be used to
> > power small cooling fans, if that makes a difference.
> >
> > Thanks,
> > Al
> >
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