Combo 12V / 9V Regulated / Filtered Power Supply

[maz]

Here's a DIY combo power supply I built using a 7812 and 7809 regulators to feed my guitar and bass pedals with constant, filtered and regulated voltages, both 9 and 12 VDC can be used simultaneously.

That's an easy project but such a device can also be quite useful to power breadboarded circuits or any other tools requiring regulated and filtered voltages. I built mine with banana jacks so I can probe current and voltage drop directly from the unit.

To power the regulators, a traditional AC to AC transformer can be used to provide 12 VAC at the diodes bridge, that will result at roughly 17 VDC (12 * 1.41) to feed the 7812 regulator, which require at least 3 volts higher than the regulated output voltage to work properly.

Alternatively, a DC unregulated wall wart adapter can also be used to feed the DC voltage directly to the regulators. To built mine I used one of those cheap selectable chinese adapters, they can be found everywhere and most of the time the output voltage is much higher than indicated on the selector. The one I used actually output 15 VDC while the selector is on 9V.

The 7812 regulator can take an input voltage from a minimum of 14 VDC to a maximum of 35 VDC, but it is recommended to stay close to the minimum in order to avoid useless heat dissipation, which will be dissipated in the regulator so the more voltage at the input means bigger heatsink.

Below is the adapter I got to built my power supply, rated at 500mA which enough for me but a 1A (1000mA) can also be used.



All you need is :

- 7812 regulator
- 7809 regulator
- Heatsinks (2)
- 220uF capacitor
- 100uF capacitors (2)
- 100nF ceramic capacitors (3)
- 1K5 resistor
- Red Led
- Transformer or Wall Wart Adapter
- 1N4007 diodes (7) * (only 3 required if wall wart adapter is used)
- An enclosure to box the circuit

* D5 - D6 - D7 are protection diodes

Combo 12V / 9V Regulated / Filtered Power Supply - Schematic and Vero Layout





The completed power supply ended up boxed inside a plastic enclosure coming from a junk car battery charger. The jumpers on the top can be removed so I can plug my DMM to probe DC current at both 9 and 12 volts outputs. Banana jacks are nice because they can be unscrewed for connecting wires, very useful to bring power on the breadboard, or when the 2.1mm jacks aren't available, but they can be swapped for some cute digital Ammeters / Voltmeters. The circuit can also be simplified, boxed inside another (smaller) enclosure with only the led and the on/off switch. If you want it done right, do it yourself!























The first live test, my circuit idles at 7.82 mA, the voltage stays at a stable 9.06 Vdc and the power supply is very quiet.



Happy DIY !