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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment. |
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12th Apr 2018, 11:57 am | #1 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
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IBM 5155 power supply
I have just completed a 21 page document on this switch-mode supply from the early 1980's. IBM did not publish data on it.
http://worldphaco.com/uploads/The_IB...WER_SUPPLY.pdf It contains a range of different circuit innovations including surge limiters that use a PUT, current detectors with a current transformer, modulated base drive for the switching transistors with current feedback to improve efficiency. One idea allows the use of a transformer with a 115V primary to be run from a 230V supply (for the 115/230V universal power input select circuit). It is a good method to synthesize what amounts to a low Z reference point that splits the incoming 230V mains in two. This idea would be suitable for running many small transformers in small 115V appliances from 230V without the need of a stepdown transformer and better than a series resistor or reactance as the method relatively independent of the load. It requires a bridge rectifier and two high value 200v electrolytic caps. |
12th Apr 2018, 8:36 pm | #2 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: IBM 5155 power supply
Quote:
That's another monumentally detailed piece of investigation, primary research and documentation. Thanks for making this contribution. I had never thought that viable, robust SMPS existed as early as this and it is high-powered and quite intricately thought out. I looked at the overcurrent sense arrangements with particular interest. Really interesting to see the two conditions you describe: *overcurrent AND *final Vout, supply, > specified limits. That's really ingenious. I also note the inrush limiting arrangement. I've never seen or heard of a programmable unijunction transistor before - really interesting to see an unfamiliar variant of a very useful circuit. Cheers!
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