Adjustable Bipolar Voltage Regulator Circuit Using LM337

Engineeering Projects

For op-amp circuits, the power supply must provide positive and negative voltages. Here is a simple circuit “Adjustable Bipolar Voltage Regulator” which gives a regulated ± 1.2V to ±2oV supply. ICs LM317K (IC1) and LM337K (IC2) are used here as positive and negative regulators respectively.

Circuit Description of Adjustable Bipolar Voltage Regulator using LM337

The circuit diagram of the adjustable bipolar voltage regulator using LM337 is shown in figure 1, and is designed using two positive and negative adjustable voltage regulator IC, a step-down transformer, a bridge rectifier, and a few other electronic passive components like resistor, capacitor, etc. The mains supply is stepped down to 22V-0-22V using a center-tap transformer and is rectified using a bridge rectifier build around four general-purpose rectifier diodes. The pulsating positive and negative DC voltage is filtered using capacitors C1 and C2,

circuit diagram of adjustable bipolar voltage regulator

The IC1  LM337 has internal feedback regulation and current passing elements. It incorporates various protection circuits such as current limit (which limits package power dissipation to 15 watts for the TO-220 package and 20 watts for the TO-3 package) and thermal shutdown. Thus these two ICs form an independently adjustable bipolar power supply.

The steel K package will easily furnish one ampere each if the heatsink is properly mounted. Variable resistors VR1 and VR2 are adjusted for each regulator to give a regulated output approximately between ±1.2V to ±20 volts. Capacitors C5 and C6 are used to improve AC ripple voltage rejection. However, if a short-circuit occurs across the regulator output, C5 will adjust the current in the terminal. The output of the adjustable bipolar voltage regulator can be calculated by the formula.

V_0 = 1.25 \times V(1 + \dfrac{VR_1}{R_1})

PARTS LIST OF ADJUSTABLE BIPOLAR VOLTAGE REGULATOR

Resistor (all ¼-watt, ± 5% Carbon)

R1, R2 = 120Ω, 0.5W

VR1, VR2 = 2 KΩ LIN.

Capacitors

C1, C2 = 4700 µF/25V (Electrolytic Capacitors)

C3, C4 = 0.1 µF (Ceramic Capacitors)

C5, C6 = 10 µF/35V (Electrolytic Capacitors)

C7, C8 = 1 µF/35V (Electrolytic Capacitors)

Semiconductors

IC1 = LM317K (Adjustable Positive Voltage Regulator IC)

IC2 = LM337K (Adjustable Positive Voltage Regulator IC)

D1 – D4 = 1N5421 (Rectifier Diode)

Miscellaneous

X1 = 230V AC primary to 22V-0-22V, 1.5A Secondary Transformer

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