This is a simple linear bench DC voltage power supply with adjustable current limit. It is intended mainly for testing logic circuits, circuits with microcontrollers and other low-voltage devices and circuits with low consumption. The output voltage can be set in the range of 1.25 to 5.5V and the current limitation 0 to 200mA. The voltage regulation uses well-known LM317 circuit. The current limiter uses a 0.47 ohm current sensing resistor (shunt). The voltage reference is regulated using TL431A and set with a potentiometer. The MC33171 op amp compares the shunt voltage to the voltage on the slider of the potentiometer. If the shunt voltage is higher, the OpAmp output will reduce the gate voltage of the MOSFET (eg IRF540) and thus limit the current. Current limiting mode is indicated by an LED. In the power supply I used a transformer with low no-load consumption, type BVEI3068016, the secondary is rated 6V 467mA 2.8VA. The output voltage at no load is approx. 10.5V and with a load of 200mA it is still higher than the nominal 6V. Thanks to this, the output voltage is sufficient to operate the voltage regulator. The rectifier bridge is made of SR160 Schottky diodes to reduce the voltage drop. Any safe transformer can be used, if the secondary is rated for at least 300mA and provides at least 8V DC after the rectification when loaded at 200mA (for the regulator to function properly). Ideally a little more, however, an unnecessarily high input voltage of the regulator increases the power losses of the regulator and the current-limiting power transistor. The 22k trimmer allows you to fine-tune the maximum adjustable current limit value, the 100 ohm trimmer the maximum adjustable output voltage.
