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Does anybody have a schematic or can point me in the right direction to construct a 12 v dc powersupply that does not need a transformer. I need to power a small dc fan and the current requirement is approx 100ma.
is there a specific reason why you need to do it without a transformer? if you want to take regular house voltage to do it you are going to need a transformer to step the large voltage down to the 12 volts you need.also there are many different 120volt fans available.there is also the possibility of using a wallwort power supply that puts the transformer and all the goodies in a box that connects dirrectly to an outlet and provides a cable that is the proper voltage that you need, just be sure to find one with the proper amount of current(amps, or milliamps) that is needed by the fan or you could have some potential problems.
Yes, these type of circuits are in wide use as mobile
phone chargers, and other small chargers.
When choosing the value for the 'dropper capacitor'
have it as low as you can get away with, because the
excess is lost as heat from the zener.
And make sure its AC working, often called 'Paper Type'
that is not polarised at all.