Constant Voltage Regulators

update.gif (1811 bytes)  29 Jan 05 - Heatsink requirements moved to a separate page.

These designs were added at the request of "Ace" from the Electric Flight List. They are intended for use as BEC (Battery Eliminator Circuit) regulators. The input voltage to the unit can be up to 25 volts and can handle a constant current draw of 1A. However, do to the heat generated at high voltages use above 15V may cause overheating (unless a suitable heatsink is fitted).

The first design is a simple 5V regulator. It uses only 3 components which are the regulator and 2 capacitors to smooth the supply. It is shown built on a piece of veroboard, but could equally be made by soldering the capacitors and leads directly to the regulator pins.

Constant Regulator Design - 5V

The second design allows the output voltage to be varied by changing the value of the included resistor. Again it can be built directly on the regulator, but it is a little more tricky. The regulation of this design is not as good as the unit above, but is more than sufficient for our needs.

Constant Voltage Regulator - 5V to 6V

Now to the tricky bit, the value of R. The equation for the value is Vout = Vreg + I'R. For the 7805 regulator the value of the I' parameter is approximately 4.5mA (0.0045A). Therefore R=(Vout - Vreg) / I' and the following table gives sample values.

Value of R
Nearest Standard
Resistor Value
Approximate Output
Voltage using Standard
Resistor (V)
5.5 111.1 110 5.50
6.0 222.2 220 5.99
6.5 333.3 330 6.49
7.0 444.4 430 6.94
7.5 555.6 560 7.52

Obviously the more accurate the value of the resistor the more accurate the output. However, due to variations in the I' value between regulators it is essential that the output voltage is checked before connection to any system.

To determine whether you need to use a heatsink, click here

Return to Plans & Designs Page