In article ,
Arfa Daily wrote:
Eh? The usual way is a series diode and that won't fail if the battery
is reverse connected. Be a bit silly if it did...


Sorry to disagree with you on this one Dave, but that's not the case.
All car radios have a diode connected in shunt with the supply. When
you connect the radio backwards, the diode conducts heavily and blows
the fuse. Usually, the diode itself fails also. The same applies to CB
radios, ham radios and PMR radios. Likewise, a couple of pieces of
portable audio equipment whose schematics I just pulled at random, also
have a shunt diode. A series diode is seldom found because apart from
anything else, it would have to be rated to carry the maximum
continuous current of the equipment, and would also cause a voltage
drop, which is wasteful of power, and not desirable for battery powered
equipment.

I'd agree with that if a high power consumer, but on something like a DVM?

In any case, the principles are not in question here. This
meter *did have* a shunt protection diode, which had failed as I would
expect it to. The OP said so.

Indeed. But only of use if also protected by a fuse?

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Dave Plowman London SW
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