| 1 Amp - Three Terminal Voltage Regulator |
| Output Voltage Selection for 3-Terminal, 1A, Voltage Regulator | ||||||||
|---|---|---|---|---|---|---|---|---|
Shown in the schematic is a simple 12 Volt, 1 Amp, voltage regulator circuit that uses a 78xx series regulator. This series includes regulators for 5, 6, 8, 9, 10, 12, 15, 18, and 24 Volts. This allows the builder to configure their supply for any one of the 78xx series regulators. Click on the buttons above the drawing to see the requirements for the various voltages.
The Power On lamp, L1, can be a NE-2 with a 68 KΩ resistor in series for 120 VAC.
Each of the 78xx voltage regulators has a Drop Out Voltage of 2.0 Volts. This means that the regulator input voltage must be 2.0 Volts higher than the regulators output voltage. This is to prevent the regulator from dropping out of regulation. This also means that the regulator input voltage must be at, or above, that voltage level, when unloaded or under full load. For the output voltage selected, the drawing will show the minimum transformer requirement.
The transformer secondary, listed on the schematic, is minimum. For best operation, choose a transformer with a secondary voltage that is a bit higher than listed. For example, a 12 VDC supply lists a transformer secondary of 10.9 VAC. A common 12.6 VAC filament transformer could be readily used, as long as it met the current requirements.
The values listed for C4 are also minimum, for 5% ripple at the input to the regulator. It is best to choose a standard value capacitor that is greater than the value listed. If a lower value is chosen, excess ripple could cause the regulator to Drop Out of regulation every half cycle.
A epoxy encapsulated Bridge Rectifier can be used in place of D1 - D4, as long as it meets the voltage and current requirements. You could also use a transformer with a Center Tap and 2 Rectifier Diodes, in a Full-Wave CT configuration. However, the estimated Secondary Voltage would need to be twice the voltage listed for the Bridge Rectifier.
A Heat Sink is recommended for the regulator. Heat sink examples might be Jameco 70771, DigiKey HS278-ND, or DIgiKey HS116-ND