# Dual Rectified 12V 5V Tapped Power Supply Safe?

Is the following regulator valid, safe and efficient?

The transformer is a dual 7V output toroidal. So B1 is supposed to rectify out 14v and B2 taps the "center" to produce 7V.

INAE and I've never used dual bridges in a tapped arrangement like this so I thought I should ask before playing around with mains like this.

UPDATE:

The following is the circuit corrected as discussed but without the regulators:

This is supposed to model the Amgis L01-6310 14V/7V transformer to see what sort of voltages might be supplied to the 12V/5V regulators (because I should have used a 12V/6V part since Vpeak of 14V is *1.414 = 19.8V. Secondaries have 7 ohms series resistance per datasheet. I have never modeled a transformer in LTSpice before but I reasoned the turns ratio is 120 / 14 = 8.57 squared = 73.5 but this seemed to be off by a factor of 2 so I figured the primary is wired in parallel for 120V mains so I doubled the ratio to 147 / 1.

Green is the 14V tap. Blue is the 7V tap. Red and light blue shows the load on the outputs.

So it seems I get 16V and 7.2V which isn't too bad. If it comes out to 16V thats only a 4V drop. But I don't think the 12V load will be loaded much. If I only load it with ~25 mA, I get 18V which is 6V * 0.025 = 150 mW.

INAE so this could all be wildly wrong. IIWAE it would probably still be wrong.

• Dave Tweed's made a good call on B2 not being required (not that it's a safety issue just not needed). I can't see a general problem but what is the currennt draw? You'll probably have in the order of 19V going into the 7812 for example so may need a pretty decent heat sink depending on the current. Commented May 29, 2013 at 14:44
• @PeterJ Yeah, I kinda order the wrong part. I see there is a 12VCT series 6V parallel that would have been better. The 12V load is very light - maybe 20mA. The 5V load is driving a microcontroller and about 10 indicator LEDs but they won't be on all at the same time so the load is going to be well below the 100mA+ limit of the 3.2VA part I ordered. Not sure if the light load helps or hurts in this case. Is there anything I can do to work-around or should I just spring for a new part? This is just a 1-off so it doesn't have to be perfect. Commented May 29, 2013 at 21:48