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Old 26th January 2013, 05:52 PM   #1
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Default Advise please

I have a problem matching an obsolete recovery diode

FMG22R

Does anyone know where best to obtain a current replacement part and which one? I need both channels.

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Old 26th January 2013, 06:13 PM   #2
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It would be more helpful to know the application so an appropriate substitute can be determined. Can you post or link the schematic?
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Old 26th January 2013, 07:16 PM   #3
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Thank you Ian. I dont have the schematic but will try to obtain one (Denon PMA 355UK). These are dual diode rectifiers in the power supply stage of the amplifer. I measured them and one seems shorted if I have measured correctly. I haven't removed them though. Something has gone to ground after slipping a probe ...
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Old 26th January 2013, 09:03 PM   #4
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I believe the R suffix is KAK type while the S suffix is AKA. For the R type there is the FEP16DTA and the S type BYW51-200.
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Old 26th January 2013, 09:04 PM   #5
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dual common anode...not in TO-220 but TO-247

not 5A but 30A

200V OK

24nS (faster)

In stock at APT30D20BCAG Microsemi Power Products Group | APT30D20BCAG-ND | DigiKey

APT30D20BCAG

The only non-match is the packaging.
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Old 26th January 2013, 09:07 PM   #6
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Well, no free downloads of PMA355 schematics from the usual sites. That makes it hard but it seems these are the main PSU rectifiers and are UF recovery types rated 220VR and 10A max. They are duals in a TO220F (fully insulated) pack and the R suffix denotes a common anode connected at the centre pin. There's no mention of being also soft recovery types but that could be seen in the datasheet if you knew what to look for.

OK - The problem is that duals are in decline generally and only the common cathode variety (the S suffix) are typically available from suppliers like On-semi, Fairchild, NXP. They still make a wide range of UF diodes, though you need both types to make a bridge rectifier, as you say, that is physically compatible with the original.

There are alternatives, like making up a bridge from single diodes such as MUR 860 or searching for NOS parts. or adapting currently available types like the MUR/MURF1620 pair. These are 200V/16Amp rated for about $2 ea from Mouser. However, they are not fully insulated, so you will need to fit insulating pads and bushes. Otherwise, their performance should be well suited.

In case you are wondering why this is necessary, take a look at what's available in fully insulated common anode types - not much at all. If someone is able to decipher NXP's parametric data pages to find if suitable common anode and cathode types are available there, I'd appreciate any help too!
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Old 26th January 2013, 09:25 PM   #7
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Many thanks everyone!

Food for thought. I have found like for like replacement Sankens on ebay but he is charging a mint. Well I need some and as you say, choice is limited.

I wonder if I would get away with a 150V 10A dual Schottky or if that is below acceptable. In any case, they are almost the same price as the Sankens.

diodes & bridge recitifiers listing page
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Old 26th January 2013, 09:38 PM   #8
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Woops- even got that wrong! MURF1620CTRG and MURF1620CTG are the 35nS recovery time, common anode and cathode versions, respectively.
What's wrong with standard UF diodes? or what's better about Schottky's as rectifiers?
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Last edited by Ian Finch; 26th January 2013 at 09:40 PM.
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Old 26th January 2013, 09:46 PM   #9
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You are correct Ian, they are of the insulated type.

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Old 27th January 2013, 07:44 AM   #10
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Quote:
Originally Posted by Ian Finch View Post
Woops- even got that wrong! MURF1620CTRG and MURF1620CTG are the 35nS recovery time, common anode and cathode versions, respectively.
What's wrong with standard UF diodes? or what's better about Schottky's as rectifiers?
Agree. I mentioned it as an alternative but there likely wont be any advantage in this design to using one or the other Ian.

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