0.7～24V continuously adjustable current limiting power supply

The circuit in the figure can achieve a continuously adjustable output voltage of 0.7 to 24V, and can achieve an adjustable maximum output current limit of 50mA to 2A.

P1 is used to set the maximum limit of output current. Adjusting it can give a current limit of 50mA to 2A at the corresponding output voltage. The principle of P1 setting the maximum limit of output current is as follows: As can be seen from the figure, the output current mainly comes from the emitter of Q4. In this way, when the output current increases, the voltage between points a and b in the circuit also increases. At this time, the voltage between point a (i.e., the e pole of Q3) and the b pole of Q3 also increases, and the voltage between the e and b poles of Q3 cannot exceed 0.7V. When the voltage between the e and b poles of Q3 increases, the e pole of Q3 will divert the current flowing to the b pole of Q4. In this way, the increase of the voltage between points a and b is limited, thereby achieving the purpose of limiting the maximum output current.

P2 is used for output voltage regulation. When the output voltage increases, the voltage between the e and b poles of Q1 also increases, which causes Q1 to shunt the current flowing to the b pole of Q2. After the conduction current of Q2 decreases, it is not difficult to see that the conduction current of Q4 also decreases, thereby reducing the output voltage. When the output voltage decreases, the principle is similar.

P2 recommends using a logarithmic potentiometer, so that the output voltage will be more adjustable and linear.

The output voltage and capacity of the power transformer should be selected according to the output voltage and current you need. The best solution is: the transformer secondary voltage is 36, 40, 48V or 50, 75, 80V with a center tap, and the capacity is 100VA.

Capacitor C1 can be selected from 2200~6800uF/35~50V.

In the circuit, BC182 is a 50V/100mA/NPN transistor, BD139 is an 80V/1.5A/NPN transistor, BC212 is a 50v/100mA/PNP transistor, and 2N3055 is a 60V/15A/NPN transistor. Q4 must use a heat sink, and it can be replaced by TIP3055.