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dsergeant · 24th Jan 2020, 12:31 pm

Thanks for all the comments, including those from Pye 405 'from the horse's mouth'. I am sceptical about some of the alleged sources of BUV28's as it is now a discontinued product. However looking at why they used a switching device I think it comes down to what was available in high voltage NPN power transistors. A big market for these is in TV switch mode power supplies where 400V and higher transistors are widely and cheaply available. I have compared the spec of the BUV28 with the common BUT11A of which I have a pile. Very similar spec, 1000V even. Lower collector current rating of 5A against 10A for the BUV28 but otherwise identical or better. I am tempted to use them.

MJE3055T definitely fails the comparison, only a 60V device and if these are the substitutes fitted in the items Pye 405 mentions I am not surprised they failed.

Dave

24th Jan 2020, 12:31 pm	#9
dsergeant Octode Join Date: Mar 2006 Location: Bracknell, Berkshire,UK. Posts: 1,172	Re: Cyrus One Thanks for all the comments, including those from Pye 405 'from the horse's mouth'. I am sceptical about some of the alleged sources of BUV28's as it is now a discontinued product. However looking at why they used a switching device I think it comes down to what was available in high voltage NPN power transistors. A big market for these is in TV switch mode power supplies where 400V and higher transistors are widely and cheaply available. I have compared the spec of the BUV28 with the common BUT11A of which I have a pile. Very similar spec, 1000V even. Lower collector current rating of 5A against 10A for the BUV28 but otherwise identical or better. I am tempted to use them. MJE3055T definitely fails the comparison, only a 60V device and if these are the substitutes fitted in the items Pye 405 mentions I am not surprised they failed. Dave