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How to build Variable DC Power Supply

2014-11-07 23:34  
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Voltage range: 0.7 - 24V

Current limiting range: 50mA - 2A

Circuit diagram

Variable DC Power Supply-Circuit diagram


P1 500R Linear PotentiometerP2 10K Log. PotentiometerR1,R2 2K2 1/2W ResistorsR3 330R 1/4W ResistorR4 150R 1/4W ResistorR5 1R 5W ResistorC1 3300μF 35V Electrolytic Capacitor (see Notes)C2 1μF 63V Polyester CapacitorD1,D2 1N5402 200V 3A DiodesD3 5mm. Red LEDQ1 BC182 50V 100mA NPN TransistorQ2 BD139 80V 1.5A NPN TransistorQ3 BC212 50V 100mA PNP TransistorQ4 2N3055 60V 15A NPN TransistorT1 220V Primary, 36V Center-tapped Secondary 50VA Mains transformer (see Notes)PL1 Male Mains plugSW1 SPST Mains switch

Device purpose:

A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it's simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. It's well suited to supply the circuits shown in this website. You can adapt it to your own requirements as explained in the notes below.


P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.You can choose the Transformer on the grounds of maximum voltage and current output needed.Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.Capacitor C1 can be 2200 to 6800μF, 35 to 50V.Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit.In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type.Excellent quality-price ratio: enjoy!

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