LM317 adjustable current stabilized power supply

The adjustable current-stabilized power supply introduced here can be continuously adjusted from 1.25A to 30A, and the output current can reach about 35A. The most common adjustable voltage-stabilized integrated circuit LM317 is used to form the core of the circuit. For detailed index parameters of LM317, please refer to the simple current-stabilized power supply circuit made with LM317. The following is a brief introduction to the characteristics of the circuit. 

In this current-stabilizing power supply circuit, T2, D5, VW1, R5, R6, C10 and relay K constitute an adaptive switching action circuit. When the output circuit is lower than 14V, VW1 is cut off due to insufficient breakdown voltage, no current passes, T2 is cut off, K is not attracted, its contact K is in the normal position, and the circuit input current is 14V AC. On the contrary, when the output voltage is higher than 14V, VW1 breaks down and conducts, T2 is also turned on, relay K is attracted, and 28V AC is connected to the circuit. This ensures that the difference between the input voltage and the output voltage will not be greater than 15V. At this time, the typical value of the LM317 output current is 2.2A. Two LM317s are used for power supply in the figure, and the output current of the entire current-stabilizing power supply circuit can be above 35A. Since the parameters of the two LM317s cannot be the same, small resistance resistors R3 and R4 are connected in series at the output end of the LM317 in the circuit to divide the current equally. 

The output voltage is adjusted by RP1 and RP2. The purpose of adding transistor T1 is to prevent the sliding end of potentiometer RP1 from having a bad contact, which would cause the common end of W317 to be open to the ground, resulting in a sudden change in output voltage and damage to the power supply and load.

The two-color LED is used as a fuse blown indicator (red light) and a power supply (orange light). When the power supply is normal, both LEDs are applied with forward voltage, and both red and green LEDs emit light, forming orange light. When the fuse FU2 is disconnected, only the red LED is applied with forward voltage, so it only emits red light. 

To ensure accurate voltage regulation, the main current loop should be wide enough when designing the circuit board, and copper wires with a thickness of more than 1mm should be soldered or tinned to reduce ripple voltage. C6 and C8 should be as close to the input and output terminals of LM317 as possible, and non-inductive capacitors should be used first. If C5 does not have a suitable capacity, several capacitors can be connected in parallel. R3 and R4 can be made of manganese wire.

During debugging, adjust RP1 and RP2 so that the relay is energized when the power output is around 14V. Otherwise, replace the voltage regulator diode and try again.