Schematic Volt

This power supply uses an LM317J adjustable regulator and an MJ2955 pass transistor. Ql and U2 as well as Ul should be heats inked. A suitable heat-sink would typically be 4` 4` 1` fins, extruded type, because up to 65 W dissipation can occur. R8 and R9 should be 1% types or selected from 5% film types with an accurate ohmmeter. Capacitors are disc ceramic except for those with polarity marked, which are electrolytic. D1, D2—1-A, 100-PIV rectifier diode. DS1—Red LED. F1 —1,5-A, 3AG fuse in chassis-mount holder. J1, J2—Standard five-way binding post, one red, one black. M1—Milli-ammeter, 0-1 mA dc. Q1—NPN power transistor MJ2955 (Radio Shack) or equiv device with a + 70-V, 10-A, 150-W rating in a -204 case. R1, R2, R7—5-W wire-wound resistor. See Notes 3 and 4 for source, or, use 17 inches of no. 28 enam wire, single-layer wound, on a 10-KOhmhm, 1-W carbon-composition resistor for R1 and R7. For R2, use 36 inches of no. 30 enam wire on a 10-KOhmhm, 1-W carbon composition resistor (scramble wound). R-4—Panel-mount, 5-kfi, 2-W or 5-W potentiometer, carbon or wire wound (See Note 8). R8, R9—See text. 51—SPST toggle switch. 52—DPDT toggle or rotary wafer switch. T1—25.2-V, 2.75-A power transformer (see text). U1—6-A, 200 PIV bridge rectifier with heat sink. See text. U2—LM317T +1.25- to 30-V, 1.5-A 7-220 regulator. Use an LM317HVK (T0-204 case) for dc output voltage greater than 40. See text.

This project makes use of a LM338 adjustable three terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up lots of electronic diagram when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the parts if 110VAC power supply input is necessary.

As shown in the figure above, the mains input is applied to the schema through fuse F1. The fuse will blow if a current greater than 8A is applied to the method. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the parts from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the diodes D1, D2, D3 & D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Diodes D5 & D6 are used as a protection devices to prevent capacitors E2 & E3 from discharging through low current points in to the regulator. Capacitor C1 is used to bypass high frequency part from the schema. Make definite that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere.