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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
A while back, there was some discussion of very cheap Chinese wall power supplies that contained just one transistor. We wondered how on earth they could possibly work.
In this video, Mike "Electric Stuff" Harrison shows the answer is "They don't"
Registered Member #941
Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497
Indeeed, and the one he got was particularly bad, usually even those cheap single transistor ones have a feedback circuit with an opto, atleast the ones i have do.
However the lack of input and output filtering is evident.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Steve Conner wrote ...
A while back, there was some discussion of very cheap Chinese wall power supplies that contained just one transistor. We wondered how on earth they could possibly work.
In this video, Mike "Electric Stuff" Harrison shows the answer is "They don't"
Maybe it uses the same setup as that single transistor 2n3055 flyback transformer circuit, I took a hand-held bug zapper apart once and that was exactly what the circuit inside it was.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Single transistor oscillators can indeed work, I have also heard of a variant of this being used on LED lamp replacements to save an expensive iron cored inductor being used.
One thing they do not like however is mains surges, as the transistor tends to short and then explode.
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How do those single transistor wall warts work?
