Dual Polarity 1i1954

[CIRCUIT IDEAS]

Dual Polarity Power Supply

DEEPAK GUPTA

SANJAY KUMAR

A power supply is the fundamental building block of all but the simplest of electronic devices. It converts the alternating current (AC) from our wall outlets into direct current (DC) at some specified voltage. A dual polarity power supply is capable of supplying +/-DC voltage. Dual polarity power supply is created mostly to power up operational amplifier circuits and other circuits that require dual supply voltage. The voltage is adjustable, requires a few parts, and easy to build. The circuit design of this dual polarity power supply is regulated with the use of a positive (LM337) and negative (LM317) voltage regulators. In the above circuit, TX1 is the center tap transformer. Each side can provide half of the output capacity of the secondary side that they split. It converts 240V AC to a lower value. Here we have used a 24VCT (12-0-12) transformer, which will supply a peak voltage of 12(1.414) = 16.97V to the rectifiers.The peak output voltage should be slightly higher than the desired regulated voltage so as to compensate for diode drop and regulator

dropout. Diodes D1, D2, D4, and D5 form the rectifying circuitry. The output of which is a pulsating DC waveform.C1 and C2 are used for filtering the output DC waveform. Whereas C3 and C4 are used to improve the transient response and filter high frequency line noise. Resistors R1-R4 set the regulated output voltage. Both LM337 and LM317 are adjustable 3-terminal positive voltage regulators, capable of supplying in excess of 1.5A over a 2V to 37V output range and -2V to -37V output range respectively. The LM317 & 337 regulators develop 1.25V across R1 and R3, respectively. This reference voltage causes a constant current to flow through the voltage-setting resistors R2 and R4 which generates an output voltage approximately equal to the following relationship: Vout=1.25*(1+R2/R1) D3 and D6 protect the regulator from damage in the event the input is shorted. Capacitors C5 and C6 improve the regulators' D3 LM317

D1

3

V0

V1

2

A/W 1

D2

+Vdc R1 120

C3 0.1uF TX1

C1 2200uF

C7 470uF

C9 470uF

R2 13K

C5 10uF

GND R4 13K C2 2200uF C4 0.1uF D4

2

1

D5

R3 120

C6 10uF

A/W V0 LM337 D6

V1

3

C8 470uF

C10 470uF

-Vdc

[CIRCUIT IDEAS] ripple rejection from 65dB to 80dB (typical) by preventing ripple voltage from being amplified at the output of the regulator.C7 and C8 are electrolytic capacitor that stiffen the output voltage and reduce output impedance. Capacitors C9 and C10 filter any high frequency noise present at the

output. The other application of polarity power supplies are Brushless DC motor testing, Aircraft ground systems, Hybrid vehicle systems, Water treatment.