This is a symmetric power supply that is based on LM7912 IC. There are two IC’s that can used in this circuit. Both of them, is using as voltage regulator and connected with zener diodes to deliver a stable DC voltage. The rectifier and filter is built by rectifier diodes and filter capacitors C1 and C4. Capacitors C2 and C5 is using to stabilize the regulator ICs. This is the figure of the circuit;
The circuit, it becomes unconventional. Both op-amps together with the driver transistors are wired as DC voltage amplifiers. The non-inverting inputs are connected to +2.45 volts through voltage dividers R2/R5 and -2.45 volts through R7/R10. A regulated symmetrical voltage extracted from the voltage divider P1/R1/R9 and subtracted from the fixed +/- 2.45 volts. The negative from IC3 and the positive is from IC4. This results to a symmetrical voltage outputs from +/- 4.9 volts to 18 volts. Capacitors C7 and C8 are stabilizing capacitors. The resistors R6 and R11 are pull-down resistors to preload the outputs in case of an empty load.
The accuracy of the voltage symmetry is dependent on the resistor values of the three voltage divider circuits. If there is non-symmetry in the output, it is probably due to one of the regulator ICs with its 10% tolerance rating. In such case, adding a 5K trimmer in series with R1 or R9 is recommended. Adjust the trimmer until symmetry is achieved.
The circuit, it becomes unconventional. Both op-amps together with the driver transistors are wired as DC voltage amplifiers. The non-inverting inputs are connected to +2.45 volts through voltage dividers R2/R5 and -2.45 volts through R7/R10. A regulated symmetrical voltage extracted from the voltage divider P1/R1/R9 and subtracted from the fixed +/- 2.45 volts. The negative from IC3 and the positive is from IC4. This results to a symmetrical voltage outputs from +/- 4.9 volts to 18 volts. Capacitors C7 and C8 are stabilizing capacitors. The resistors R6 and R11 are pull-down resistors to preload the outputs in case of an empty load.
The accuracy of the voltage symmetry is dependent on the resistor values of the three voltage divider circuits. If there is non-symmetry in the output, it is probably due to one of the regulator ICs with its 10% tolerance rating. In such case, adding a 5K trimmer in series with R1 or R9 is recommended. Adjust the trimmer until symmetry is achieved.
