In case you assess the cost and the rating of this simple variable bench power supply you may receive a big surprise, as the output voltage and current tend to be totally variable between 0. . . 18 V and 0 . . . 1.8 A correspondingly and expenses have yet been maintained affordable. Referring to the circuit diagram: the input consists a 220V mains switch, fuse, transformer, bridge rectifier and a filter capacitor (C2).
Diode D5 and capacitor C1 create a negative supplementary voltage, that is stabilized through zener diode D6 and capacitor C4.
The negative voltage offers the negative supply for the two lCs. Pretty much everything is essential to help the output voltage to become fine-tuned lower to zero volts.
Throughout the development of this section of the circuit keep in mind that the positive terminal of electrolytic capacitor C4 is hooked up to ground! Control is given by lC1 and IC2. Capacitor C3 inhibits any kind of surplus transients at the input of IC1 and it also must for that reason be attached as strongly as you can to IC1 (similary C4 and lC2l.
The reference point output from pin 4 of IC1 would go to the voltage divider composed of R5 and P2 (this particular pot fixes the value of the output voltage). lC2 is actually linked like a differential amplifier and analyzes the signals at its two inputs.
The variation amongst the inputs may be the voltage drop throughout ‘current’ sensor R4. This specific lC feeds the current sensing input (pin 2) of the L200.
P1 within the feedback hook of the 741 is employed to change the output current in the circuit. IC1 has to be attached to an appropriate heat sink because it emits almost all the power of the circuit.
This simple variable bench power supply circuit may without difficulty be constructed into a box along with a voltmeter and ammeter attached to the front board. Because of the precision of the circuit all these must essentially be electronic meters, however almost any sort will work.