# Power supply/ current supply design

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#### inkedallusion

##### New Member
I am working on a custom designed power supply for my tattoo equipment. I am looking at a commercial bought power supply and it basically is an unregulated power supply. When I hook the leads to the output, it reads 39 volts. It uses a non-center tapped transformer, which reads 28.4 Vac across the secondary. This goes to a bridge rectifier rated at 2 A output and 400V. The filtering caps are 1000uF electrolyctic at 200WV. This is all fed to a 25W 25 Ohm rheostat. I am trying to figure out if a regulated supply is a better idea, and why the commercial supply is unregulated. I have studied how to design unregulated supplies, but I am not sure what the load on the supply will be once I hook my tattoo gun up to it. Are the 200 V caps really necessary? That seems like overkill to me. What about the power rheostat? Does it have to be a 25 Watt? Also, I have looked at specs on other supplies and they are usally around 15 volts and 1.5 amp and are regulated. Can anyone help me?
Eric

#### Phasor

##### Member
My opinion is that a regulated supply is almost always better.

There is really only one reason to choose an unregulated supply over a regulated supply: That is \$ money. If a manufacturer sells to unsuspecting customers who don't know the difference, they can make more profit on an unregulated supply.

The reason for the 200V capacitors, is probably just a safety factor. Better to overrate them, than underrate them (bearing in mind that the peak secondary voltage is about 40V)

For your purposes, probably a simple 3-terminal regulator will do the job. (either 78xx series or an adjustable one, like LM350K)

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