On 08/04/2021 08:48, Peter Able wrote:
On 08/04/2021 09:30, Jeff Layman wrote:
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. With a bridge rectifier three of the
diodes are effectively redundant (unless one goes short-circuit), 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.


A single diode only passes 50% of the mains, a bridge or a full-wave
passes 100% - so less ripple on the output - or a cheaper capacitor
results.


It's not always mains AC. Sometimes an appliance provides something like
24v ac output for peripheral devices, like a remote transceiver, or a
home automation device.

After rectification you may need to also reduce the voltage with
something like a voltage regulator. Which AIUI is basically resistance
and hence power inefficient.

The question I had is might a half wave rectifier be better (than a full
wave rectifier) to convert 24v ac to 5v dc, i.e give the resistance less
work.

In the end I gave up and decided it was better to use a USB wall plug
transformer, but it was something I have pondered upon since.