Dual ±15VDC / ±21VAC power supply

Cremona, January 2019.
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This shows a super simple dual voltage power supply, that generates ±15 volts, DC. The schematic is based on the voltage regulators 7815 and 7915. The first one is well known, it generates 15 V stabilized. The second one is its counterpart, generating -15 V. The schematic follows:


As a brief description, the transformer generates ±18 V, alternated current. From the central pin we take the 0V, while the other two will be rectified by a diode bridge and leveled with two large capacitors. Two smaller capacitors are also used, and their purpose is reducing noise (due to the lower ESR with respect to large electrolitic ones).

Then, the positive branch of the rectified bridge (at about 21 V) goes to a MC7815 (equivalent to L7815), that brings down the voltage to +15 V. The negative branch goes to the MC7915, that generate the -15 V. Note that the values +15 and -15 V are referred to the center pin of the transformer, which is our reference at 0 V. Check the datasheet of these two components for the pinout!!! The maximum current is limited by them.

You can add a cool switch and a LED, to indicate when the circuit is ON. Here's a pic of the (a bit messy..) assembly. I added three external connectors for the alternated voltage, which is about ±21VAC (unloaded).


And here is the final product, in a cool cheap plastic instrumentation box! You can find these boxes on ebay, they cost from 5 to 10 euros, or a bit more if you need a faster delivery.


Any comment? Feel free to write me!

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