Transformerless 12 v power supply

[bryan]

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.

thanks

-=Bryan=-

 

[chubs1646]

12v power

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.

 

[Nostrafus]

Why not just use 8 AA's ?... Probably cost you less.

Or am I just being a smartass about this one ?

 

[john1]

Hi Bryan,

These little transformerless modules that supply low
voltages at low currents usually use a capacitor as a
'dropper' at least thats my experience.

It has to be AC working of course, and simply wired in
series with a small load.

It has to be mentioned that a fuse for the load is in my
opinion very necessary, because a dirty pin or any poor
connection can cause vastly excess current to flow in
the load.

For a small fan such as you describe, i would suggest
a capacitor of 2 or 3 mfd, i am guessing that your
main supply is 110v it seems more common than mine at
240v.

The load would be a small resistor of about 200 ohms
and a diode bridge to give you the DC.

Across the diode bridge put a 12 volt zener and a small
electrolytic, maybe 30 MFDs or so.

The zener has to be about 2 or 3 watts, and with no
load on the supply it may run barely warm.

I have made many such supplies.
Best of luck with it,
John

 

[bryan]

Hi Bryan,


Thanks for the help John, can such a supply handle 100 -125 ma .

I have made many such supplies.
Best of luck with it,
John

 

[john1]

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.

Best of luck with it, John

 

[rajavelT]

This can help you I think..

dear friend this is the URL for transformer less power suppl
http://www.mitedu.freeserve.co.uk/Circuits/Power/tps.htm
bye and have fun
Raj from india