Diode identification?

Any chance of reverse-engineering the bit of the circuit it is used in, and producing a bit of a circuit diagram?

It's probably not too tricky to acertain it's likely rating and speed by judicious examination of where it lies in the gubbins.

Graham

Thus spake Palindr?me:

Not very good at this... just a component-test monkey (c:

But it (and its partner) seems to be across a c.t. winding of the SMPS transformer. Electrolytic filter caps "downstream" from these are rated at

25v.

There are a dozen more of this type of diode in this SMPS, across other trans. windings.

This is a multiple-voltage ps inside a 240v ac motor controller in a Japanese printing press.

Thanks,

If it's on the secondary side, it will not be a 'normal' 1A diode. It will be a high speed Schottky type. If you try to use a standard silicon rectifier diode, it will run very hot and fail, in short order.

Arfa

If testing it shows slight reverse leakage - it could be a Shottky-barrier type, Most DMMs have a diode forward voltage test if the Vf is less than about 0.4V and more than 0.1V it almost certainly is SB, if its glass encapsulated - consider the possibility it's a zener, these show Vf about

0.7V, regular diodes show about 0.6V and fast silicon types usually somewhere around 0.55V.

But if any of these tests pass - it's probably OK anyway!

Thus spake ian field:

The other diode ("good" one) in the circuit measures 0.4v in DMM diode test (Fluke meter). Not glass, epoxy (black stuff).

Infinite both directions, according to diode test on the DMM.

Is SB type used as rectifier in SMPS? Or is vanilla Schottky used in this application?

Thanks,

Is "the other one" with 0.4Vf identical to the one you've taken out?

Thus spake ian field:

Yes, same markings. They're apparently a backward-connected set of rectifiers across a SMPS ct transformer secondary.

Thanks,

You mean the anode ( or cathode ) of the diode is directly connected to a reservoir cap ? It'll be a rectifier on the secondary side. It needs to be a high speed type and from your mention of 25V, I'd probably use a 200V part ( for safety's sake ). Current rating - you say it looks like 1A - would suggest a UF4003 replacement. Are you sure about the current rating though ?

Graham

Not necessarily Shottky actually. ( btw - is it *meant* to have a 'c' in it or not ? )

Oh I don't know. A subcontractor once fitted a 1N4004 where I'd specified a UF4004 on a lightly loaded secondary. It ran for many hours before failing !

They did it second time round too ! I reckon that purchasing looked at the part number and reckoned they could substitute. Lovely stuff working with Asians.

Funny thing was, my colleagues looked glum since it was our first smps design. I ( in my infinite wisdom ! ) smelt a rat and went to it almost straight off. It was shorted. Just made the thing go into hiccup mode.

Graham

Thus spake Pooh Bear:

(That's a paid-subscription link...)

Re. the current rating, I'm just comparing the unit in question with a non-schottky, vanilla 1A rectifier. They are similar in size.

Thanks,

SB = Shottky barrier. Techy speak for 'shottky'.

Graham

Yabbut.... It gave a list of UF400x devices which I didn't find anywhere else quickly. You can get the data easily with a bit of common sense. Oh sod it.....

get the pdf

I ask for a reason. Do you know the current draw on the supply ? It pays to fit a beefier device if unsure.

Graham

The thickness of the wires coming out is often a better indication than the size of the body.

IIUC, you aren't going into production with this thing, just trying to get it working. So you can afford to err on the side of safety and put in a well over-spec'ed schottky, even though a much lower spec'ed (i.e. lot cheaper) device would be fine too.

Any idea why it failed?

Thus spake Palindr?me:

Nope. There are 4 identical controllers. They've all been purring along for near 10 years without a hiccup.

Thus spake Pooh Bear:

Not to get too bogged down in terminology, but sb = schottky barrier = schottky ?

Thanks,

Thus spake Pooh Bear:

Like this?:

I need it today and nte is the only maker available locally over-the-counter.

Thanks,

Stuff gives up after a while sometimes !

Graham

Yes. The barrier bit is optional if you like. It's about the junction inside the device. Like pn junctions. Except this one is a barrier. If one cares to be verbose, ordinary silicon diodes could be called junction diodes.

Graham