Can anyone cross reference these zeners please?

[Chris Wilson]

Circuit is for a small (missing) board for a huge Farnell 60 volt, 50 Amp linear power supply. I have a smaller version that is complete and working, but the schematics are a bit different, although somewhat similar. I have got together most of the bits to build a new board, and will have it remote and not plugged into an edge connector strip, to keep board manufacture simple. There should be a small schematic attached, but I have the full size one at http://www.gatesgarth.com/supplies.jpg  The diodes in question are the three zeners. I can't find any data on these numbers. Maybe someone with a deeper understanding of the circuit can suggest equivalents? Thanks!

[Paul Price]

The part numbers give away their voltage identity, but the M56, but from the more complete schematic it is a 5.6V zener rather than a 56V zener the designation implies, but the two on the right are surely about 5W and 15V and need to be matched.

[Chris Wilson]

Thanks Paul, is that enough info to source suitable substitutes? How can you tell the IZM15 is a 1 watt device? It may be a 1ZM15, the schematic is not that clear. Any way to ascertain the wattage of the 56 volt device? Or should I just choose something beefy? Cheers.

[Paul Price]

Now that I see the rest of the schematic, the MR56 is actually a 5.6V zener, 1W and setts the bias for the two 15V in series zeners.

For the 5.6V zener 1W would be fine, 10% tolerance.

The 15V zeners should also be at least 5% precise voltage tolerance and they may have to be closely matched in voltage at 150mA of test current from a collection of them. Since the 15V zeners are also part of a crowbar protection circuit, this is another reason the 15V voltages here might need to be precisely set. The 15V zeners may have to be 5 Watt zeners mounted on a heatsink.  Be advised, the 82 ohm at the collectors of the 2N3053's, needs to handle up 3 watts of power under overload conditions,and the pair of 39 ohms at the emitters (at least  1W)  and the 2N3053s will require a  heatsink.

[Chris Wilson]

That's great Paul, thanks again. If you want to see the rest it's at http://www.gatesgarth.com/farnell/farnell.html  The scans aren't great, but should be readable. Have a good weekend

[Paul Price]

I looked at the pictures, rough as they are, and I can see there are still some lights missing from this Christmas tree.