EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: okest on November 16, 2017, 07:18:08 am
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Hello,
I need to create an variable voltage power supply(AC->DC) with output from around 3V to around 50V(around those voltage levels) and nominal max current of 7A(so i was thinking maybe rating the supply for 10A would be good enough).
I was thinking of using variable autotransformer with 1500VA rating and a KBPC5010F 1000V 50A diode bridge and using caps to filter the output a little. Since the variable autotransformer steps would be too steep i think(adjustable from 0-250V) i was thinking of using another transformer with like 230V->110V feeding it straight from variable autotransformer. What problems would i run into and do you have any suggestions on what should i do before i go buying stuff and finding out the hard way?
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An autotransformer would provide no isolation from the line voltage, and would be incredibly dangerous to use as a bench supply
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An autotransformer would provide no isolation from the line voltage
That's why the 230->110V transformer proposed by OP would help. With both voltage range, as well as isolation from mains.
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Better a 230V to 55V transformer. A bridge rectifier feeding a capacitor only delivers 2/3 the DC amps of its AC RMS input current, so for 7A out, you need a minimum of a 10.5A transformer secondary, which at 55V is 578VA, a 600VA transformer will have a little margin. Use a 110V output transformer and it will need to be 1200VA which wlll be a lot more expensive. Also the lower voltage gives you more control range.
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Why on Earth do you need a 50KW rectifier for a 350W power supply?! :wtf: That seems incredibly excessive. Or am I misunderstanding something...
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Well if you've got it sitting on the shelf . . .. .
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Why on Earth do you need a 50KW rectifier for a 350W power supply?! :wtf: That seems incredibly excessive. Or am I misunderstanding something...
It's not a 50kW rectifier. It's a 50A rectifier with a reverse standoff of 1000V. You wouldn't describe a 1N4007 as a 1kW diode rectifier.
Admittedly it is a bit high rated - not excessively so for OP's original idea of 0 - 250V. Obviously for a 0 - 55V as suggested by Ian.M the voltage rating could be dropped to, say, 200V and the current to maybe 20A (if it's going to be driving a capacitive load).