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Old 13th July 2012, 08:45 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default What's wrong with a PSU like this?

So I was thinking about how a bit of PWM could be used for a switching mains supply and I wonder if these PSUs already exist if not why not?

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Basically the mains is rectified to DC then goes through the FET which is driven my the 555 timer configured in astable with variable duty cycle which can be adjusted with the duty adjust pot. The resistor connected to the FETs source is just in parallel with the lod to maintain a small amount of current being sunk when there is no load attached. Again the the resistor connected across the output is there to draw a small amount of quiescent current for when there is no load attached. The feedback can be implemented in the 555 circuit for better output voltage stability.

I was thinking the main concern is going to be with safety?

What would efficiency be like as well as PF?

Would, in principle, this circuit work?

I might give this a try with some low voltage in a week or two.

Thanks
Boscoe
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Old 13th July 2012, 09:01 PM   #2
DF96 is offline DF96  England
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Safety nonexistent. Efficiency could be good, unless you add a transformer to make it safe.

Don't try this at home - it breaks forum rules!

Last edited by DF96; 13th July 2012 at 09:02 PM. Reason: edit
 
Old 13th July 2012, 09:16 PM   #3
Boscoe is offline Boscoe  United Kingdom
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Yes it's high voltage and I know it's DC but what's makes DC high voltage so dangerous I work with 400V 3 phase on a daily basis.
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Old 13th July 2012, 09:20 PM   #4
DF96 is offline DF96  England
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It's not the DC which is dangerous but the direct connection to mains. Mains is a high voltage combined with very low impedance. Some people can work safely on high voltages, but you would not want bare live wires hanging around in your house.
 
Old 13th July 2012, 11:16 PM   #5
kevinkr is offline kevinkr  United States
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Discussion of unisolated mains operated supplies such as the one discussed in this thread are a violation of forum policy, and such supplies are blatantly unsafe. Thread closed
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