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Circuits designed by David Johnson, P.E.
Last Updated on:
Wednesday, December 20, 2017 06:09 AM
List of Dave's Circuit Designs
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Miniature AC to DC Power Supply
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| Electronic systems are getting quite
efficient these days. I seldom design a small product that requires more than 100
milliwatts of power. Often, if the product is not going to be powered by batteries,
it requires a wall mounted AC to DC power adapter or a small on-board power module.
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The smallest power module around is made by Bias Power. As shown below, this thing does
not take up much space. But, if all I need is 100 milliwatts, this 1 watt device is
overkill. |
What I would like to see is a smaller 4 pin single inline package (SIP) device, similar in
shape to the solid state relay shown below, which contains a universal fully isolated AC
to DC power supply. I would not mind if the thing had a low overall efficiency. It just
has to be small and robust. The DC output might be rated at 3.3v, 5v or 12v. |
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With a low power requirement, perhaps
a different circuit topology could be made to work. One way to do this AC to DC
conversion is shown below. A series capacitor limits the current into a
conventional bridge rectifier and filter capacitor front-end circuit. A 24v zener
diode limits the DC input voltage to a miniature isolated DC to DC converter. The
converter output then provides a nice DC output. |
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DC Magazine, January 2011, Page 6: Miniature AC to DC Power Supply |
