0-30V adjustable voltage stabilized power supply circuit based on LM317

0-30V adjustable voltage stabilized power supply circuit based on LM317 (1)

It is very convenient to use LM317 to make an adjustable regulated power supply, but the minimum output voltage of LM317 is 1.25V and cannot be adjusted from 0V. Here is a simple circuit that allows the output voltage of LM317 to be adjusted from 0V.

The LM317 in the picture is a familiar three-terminal adjustable voltage regulator IC. Its maximum input voltage is 40V, the output voltage can be adjusted from 1.25 to 37V, and the maximum output current is 1.5A.

In this circuit, the power transformer has two secondary stages, one with an output of AC30V and the other with an output of AC6V. After AC30V is rectified by four 1N4002 diode bridges and filtered by capacitors, a DC voltage of about 36V is generated and applied to the input end of LM317. After the AC6V voltage is rectified by the diode and stabilized by VD, a DC voltage of approximately -1.25V is generated. The ① pin (adj terminal) of LM317 is connected to the voltage of -1.25V through the potentiometer RP. When the output voltage of LM317 is adjusted to 1.25V, the 1.25V output by it offsets the -1.25V voltage generated by VD, so that the output voltage of LM317 It can be adjusted to 0V.

When the resistor R1 is 120Ω and the potentiometer RP is 3KΩ, the output voltage range of this circuit is 0~31.25V. The output voltage can be changed by adjusting the resistance of RP.

If this circuit wants to output a voltage of 0V, the voltage stabilization value of the Zener diode is required to be 1.25V. In practice, it is not easy to buy a Zener diode with such a small voltage regulator value. If the requirements are not high, you can choose two 1N4001 diodes connected in series to generate a -1.25V reference voltage. When the operating current of 1N4001 is controlled at a few mA, its forward voltage drop is approximately 0.6V each.

In order to facilitate the adjustment of the output voltage, it is best to use a multi-turn potentiometer as the potentiometer RP in the circuit.

By the way, since the output voltage of this voltage stabilizing circuit is at least 0V, the voltage difference when LM317 is working may be very large. When working at high current, LM317 will seriously heat up, so when making LM317, an external circuit with a large enough area must be added. heat sink. In addition, the secondary AC voltage of the transformer should not be too high, otherwise the DC voltage generated after rectification and filtering may be higher than 40V, causing damage to the LM317.

0-30V adjustable voltage stabilized power supply circuit based on LM317 (2)

A 0-30V adjustable regulated power supply can be made using a series-connected regulated power supply with discrete components or a LM317 three-terminal voltage regulator block. The circuits are all typical circuits.

To be careful of:

1. If it is necessary to start from 0V, a negative voltage lower than zero potential (input and output ground) needs to be set;

2. The greater the input/output voltage difference of the series regulated power supply, the greater its power consumption. Therefore, the input voltage can be set in steps to reduce power consumption.

Stabilized power supply generally consists of three parts: transformer, rectifier and voltage regulator. Transformers convert commercial AC voltage into the necessary low voltage AC. Rectifiers convert AC power into DC power. After filtering, the voltage regulator changes the unstable DC voltage into a stable DC voltage and outputs it.

Principle description of homemade 0~30v adjustable DC stabilized power supply

DC stabilized power supply is a device that converts 220V industrial frequency AC power into DC power with a regulated output. It requires a transformer circuit, a rectifier circuit, a filter circuit, a voltage stabilizing circuit, a voltage output indication circuit, a buzzer alarm circuit, and a signal Processing indication circuit.

The rectifier circuit uses the rectifier diode IN4007, whose pins are divided into positive and negative. The white strip is the negative pole, and the other side is the positive pole.

The voltage stabilizing and adjustable integrated chip LM317 adopts a chip imported from ST, which has reliable quality and high output voltage and current stability. The two red wires of the step-down transformer are connected to the 220V mains power, and the two black wires (or blue wires) are connected to the output 36V AC power.