Help with a Diode

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I've had a failure in a circuit operating a 12/240V refrigerator. The
compressor works at 24VAC. The fault is in the 12VDC step up to 24VAC
circuit.  I have procured the obviously failed components, but understand a
couple of diodes may be critical and would be worth replacing.  In the
circuit are two diodes marked 30D2.  I have its data sheet.    The local
(professional) electronics outlet in Bowen Hills sold me IN5404s and told me
they would replace the diodes I need.  Are they correct?  I wasn't overly
impressed with the lack of confidence on the other side of the counter.

The 30D2 datasheet says the VRRM is 200V and the NRSM is 400V.  For the
IN5404, these are 400V and 525V.

Io for the 30D2 is 1.7A at 40deg and 3A at 61deg, whilst Io is 3.0A at
105deg the IN5404.
IFSM for the 30D2 is 150A whilst it is 200A the IN5404

Can anyone comment on whether the IN5404 is a good substitute for the 30D2
please?  Or is more needed on the circuit?
Thanks folks.


No flames please, I'm a mug at electronics.

Re: Help with a Diode
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    Without going into the specs of both diodes in detail, superficially
it looks like a 1N5404 should be able to replace a 30D2.

    It depends on what the diodes actually do in the circuit, as to
whether or not any subtle differences like forward voltage drop would be

    If the original 30D2 diodes are measuring OK (conducting in the
forward direction and not leaking in the reverse direction), there's
probably not much point replacing them. Diodes don't usually 'half fail'.

    Hope this is of some help...


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