Dual Adjustable Power Supply Circuit Lm317 Lm387.docx

Dual Adjustable Power Supply Circuit Description Power supply is a circuit based electronic device that supplies the needed electrical energy to an electrical load. Power supplies can also be named as electric power converters as they are used to convert electrical energy from one form to another. Power supplies are used in everyday consumer devices and PC’s. In such devices the power supply unit is inbuilt along with their loads. The power supplies that we are going to discuss are more discrete and are useful for simple projects and minor electrical applications. The aim of the dual adjustable power supply circuit is to provide power for other projects that require a dual (+/-) adjustable power supply. This is the circuit diagram of a dual adjustable power supply using IC’s LM 317 & LM 337. LM317 is able to deliver a maximum of 1.5 A at a range of 1.2 V to +30V. LM317 is a positive voltage regulator and LM337 is the negative compliment voltage regulator IC of LM317. The LM317 IC is a 3-terminal voltage regulator that is designed to supply in excess of 1.5 Amps of a DC output voltage range of (1.2-30) Volts. These IC’s also have a special TO3 package and if assembled with a large heat sink (HS07051 preferably), the power supply can be designed to handle load current to its max. They also have a built in short circuit protection.

Refer: LM317 Voltage Regulator Circuits

Here the circuit is wired to produce a dual adjustable output of ( +15 , 0 , -15 ). The capacitors C1 to C8 provides filtering and ripple rejection. Resistors R1 & R2 controls output of LM317. Resistors R3 & R4 controls the output of LM337. R1 and R4 can be turned to vary the positive and negative voltages. This circuit is a must on an electronic hobbyists workbench.

If needed two LED indicators can also be connected to indicate the positive and negative power outputs. A Blue LED can be connected across U1 and GND and a Red LED can be connected across U2 and GND. The Blue LED can be kept as an indicator for positive power and Red indicator can be kept as an indicator for negative power.

Notes 1. The transformer should be anything that produces a min of 3 A with (24 0 24 ) output voltage. 2. The voltage range can be further increased by increasing transformer output within the limits of IC. 3. Do not connect a load drawing more than 2A at output. The IC,s must be fitted with heat sinks for better protection.

Parts List Component

Specification

Name

C1, C2

2200 uF

50V Electrolytic Capacitor

C3, C4, C5, C7

2.2 uF

50V Electrolytic Capacitor

C6, C8

100 uF

50V Electrolytic Capacitor

R1, R4

5K Ohms

Potentiometer

Component

Specification

Name

R2, R3

220 Ohms

1/4 W Resistor

D1 to D4

IN 4007

Diodes

S1

SPST

2 Ampere Switch

U1

LM317

Voltage Regulator IC

U2

LM337

Voltage Regulator IC

T1

24-0-24

Center Tapped 2 Ampere Transformer

Extra Heat sinks for two IC's , Power Cord, Casing, Wires

Dual Adjustable Power Supply Circuit Diagram.