For op-amp circuits the power supply must provide positive and negative voltages. Here is a simple circuit “Adjustable Bipolar Voltage Regulator” which gives regulated ± 1.2V to ±2oV supply. ICs LM317K (IC1) and LM337K (IC2) are used here as positive and negative regulators respectively.
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 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 are properly mounted. Variable resistor 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 adjustable bipolar voltage regulator can be calculated by the formula.
V0 = 1.25V(1+VR1/R1)
PARTS LIST OF ADJUSTABLE BIPOLAR VOLTAGE REGULATOR
Resistor (all ¼-watt, ± 5% Carbon)
R1, R2 = 120Ω, 0.5W
VR1, VR2 = 2 KΩ LIN.
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)
IC1 = LM317K
IC2 = LM337K
D1 – D4 = 1N5421
X1 = 230V AC primary to 22V-0-22V, 1.5A Secondary Transformer