"Jeff Layman" wrote in message
...
On 07/04/2021 23:46, John Rumm wrote:
On 07/04/2021 21:42, ARW wrote:

Am I correct in saying that it does not matter if there is a LN reversal
on the input?

Correct...

It will always have a correct +/- DC voltage.

Yup.

In fact if you are designing DC powered kit that runs from an external
supply, then sticking a bridge rectifier on the input even though you
are only ever expecting DC rather than AC, is a way to ensure your kit
will never see the input polarity reversed if used with the wrong PSU.

Surely you only need a single rectifier connected the right way round in
either the +ve or -ve line.

Yes.

With a bridge rectifier three of the diodes are effectively redundant
(unless one goes short-circuit),

Nope, they allow the device to work regardless of how its powered.

and you've got a double voltage drop across the diodes to take into
account. That might be significant for the equipment - a bit like trying
to use NiCads instead of alkaline-manganese batteries.

Even if you're trying to cater for the extremely rare short-circuit
mentioned above, you still only need two diodes.

Yes.