Laboratory power supply 2-28V / 2.5A

The revival of home-built electronic devices is difficult to do without a controllable source, also called laboratory. The classic of these sources is the connection with the integrated stabilizer LM723 controlling the power transistor. Allows you to set the output voltage in the range 2 – 28V at a maximum current of 2.5A. The power supply has short-circuit and overload protection.

Laboratory resource circuit diagram and principle of connection

The Graetz rectifier is used to obtain a DC pulsating voltage from the AC supplied by the transformer. Capacitor C2 is used to smooth the voltage, C1 is blocking. The setting circuit consists of resistors R1, R2 and potentiometer P1. The comparator inside the LM723 stabilizer compares the voltage supplied from this circuit and from the source output (via the R3 and R4 dividers). Capacitor C3 provides frequency compensation. The output voltage of the LM723 stabilizer is a controlled transistor T1, which controls the power transistor. When the source is loaded, the output current flows through resistor R5. Voltage drop, which is created on it is used in the LM723 circuit as short-circuit protection, resp. overload. Capacitor C4 covers current spikes.

The connection must work for the first switch-on. If not, some component is bad, or we made a mistake while connecting. If the circuit breaker trips, the output voltage drops to zero. Short circuit (overload) remove and turn the power off and on again after a while. I recommend supplementing the source with voltmeter an ammeter.

List of parts for a laboratory source