This is the variable DC power supply circuit. This power supply has regulated output, can be adjusted from 3 to 25 volts and the current output is limited to 2 amps as shown, however it may possibly be improved up to 3 amps or more by applying a smaller current sense resistor (0.3 ohm). Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. The 1458 may be substituted in the circuit, but it is suggested the supply voltage to pin 8 be limited to 30 VDC, which can be achieved by adding a 6.2 volt zener or 5.1 K resistor in series with pin 8. The 2N3055 and 2N3053 transistors need to be attached on proper heatsinks and the current sense resistor must be rated at 3 watts minimum.