Tuesday, August 19, 2014
Variable DC Power Supply
Parts:
P1____________500R Linear Potentiometer P2_____________10K Log. Potentiometer R1,R2___________2K2 1/2W Resistors R3____________330R 1/4W Resistor R4____________150R 1/4W Resistor R5______________1R 5W Resistor C1___________3300µF 35V Electrolytic Capacitor (see Notes) C2______________1µF 63V Polyester Capacitor D1,D2________1N5402 200V 3A Diodes D3_____________5mm. Red LED Q1____________BC182 50V 100mA NPN Transistor Q2____________BD139 80V 1.5A NPN Transistor Q3____________BC212 50V 100mA PNP Transistor Q4 __________2N3055 60V 15A NPN Transistor T1_____________220V Primary, 36V Center-tapped Secondary 50VA Mains transformer (see Notes) PL1____________Male Mains plug SW1____________SPST Mains switch Notes: * 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-schema. In some cases the rear panel of the metal box in which you will enclose the schema can do the job. * The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type
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