Re: Heads Up for Power Supply deal...

As you said in a previous note, we are picking on this one...

I agree that on a typical switched supply (or a raw DC one) the internal rectifier diodes would normally prevent too much reverse
voltage. The problem comes when it is not a typical supply.

There are switchers that use SCR's with fancy commutation circuits; relay delayed or electronically controlled output circuits; internal
series diodes to avoid damage from positive voltage being fed into it (when used for battery charging or with free-wheeling motors).

This specially applies to unknown surplus supplies since typically we do not know what application they were designed for.

Adding the diodes removes possible problems if the person happen to have an unusual supply.

Bertho
======================================
From: Jon Elson <jmelson@...>

>
> Bertho Boman wrote:
>
> > From: Bertho Boman <boman@...>
> >
> > Not so fast Jon. Typically it is safe as you say but depending on the circuitry, there might also be sense amplifiers, over current
> > protection and not to forget electrolytic output capacitors that might be fed 18 volts in reverse. That can be ugly!
>
> But, that shouldn't happen, as the diodes already in the power supply will hold the
> reverse voltage to 0.7 V maximum.
>
> Jon