piclist 2002\09\24\084853a >
Thread: 2-tran SMPS 5v reg now 90% efficicient!
face BY : Russell McMahon email (remove spam text)

>  My only concerns about using it in a product is the lack of overvoltage
> and overcurrent protection. It would not be nice to have 100 bucks going
> away because the switching transistor got short circuited :-(

I have my 3 transistor version in service with unknown thousands in use so
far. I have had a very few failures reported to me although how many I don't
know because the system they use has no mechanism for reporting this back -
this is not under my control at all and not how I would like it to be.
(Designed in NZ, made in Taiwan, sold in Europe :-) ).

Because I didn't want a failed pass transistor etc to take out the low
voltage electronics I specd a fused output with a 12v zener behind the fuse.
(1w glass bead body DOxx Philips can't remember the number and too lazy to
go and look it up). Zeners almost always (essentially always) fail short and
the leads on these are like mini crowbars compared to PCB tracks etc. All of
the (few) failures I am aware of have shorted the zener and blown the fuse
without hurting the low voltage electronics. Arguably a reasonably cheap way
of protecting against failure but may cost almost as much as Roman's whole
converter :-)


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Subject (change) 2-tran SMPS 5v reg now 90% efficicient!

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