Variable Power Supply using LM317 Voltage Regulator

Простой регулируемый блок питания

Sooner or later, every newbie ham needs a simple variable power supply. If there is not enough experience or skills to build serious circuits, then the Power Supply using LM317 will do just fine. This simple Power Supply with voltage regulation has been tested by more than one generation, its circuit operates stably and reliably.

Scheme of Variable Power Supply using LM317

We will assemble a Power Supply with a maximum voltage of 12 volts in the output according to this scheme, such voltage will be enough to power most self-made circuits.
Scheme of variable power supply using LM317
When choosing a transformer, it is important to take into account that the LM317 input voltage of the Power Suppl must be at least 3 V higher than the maximum desired output. The diode bridge must be chosen with a current of at least 2 A.

The basis of the Power Suppl is LM317, it is an adjustable integral voltage regulator, which is included by the standard scheme. The LM317 will draw a maximum current up to 1.5 A (if the transformer allows), and the output voltage can be adjusted from 1.25 V to 37 V, it is calculated by a simple formula.

U out = 1.25 (1 + R 2 / R 1 )

For this scheme is better to take the resistor R1with the power of 0.5 W, its nominal value ranges from 200 to 300 Ohm. Resistor R3 can accurately correct the maximum output voltage. Condenser C5 is necessary for smooth voltage regulation, but optionaly you can do without it. The diode VD1 protects the LM317.

Simple Variable Power Supply using LM317 – How to make?

The base of the circuit is assembled on the breadboard, it contains a minimum of details, the diode bridge and the condenser C1 are on the other board. LM317 must be installed on the radiator. Our transformer produces only 0.75 A, so the LM317 will work only at half power.
How to make a variable power supply
All of this is easily fit into the old case, and for a good indication of the output voltage a digital voltmeter is set up.

The circuit works immediately and does not require complicated adjustment, it is only needed to accurately correct the maximum output voltage by the resistor R3.
Simple a variable power supply
That’s how we got a simple Power Supply with voltage regulation. Now we will test how it works. The output minimum voltage is 1.25 V.
power supply on LM317 How to make
The output maximum voltage was set to 12 V.
Power Supply on LM317
Simulation of a shortcut will not harm the Power Supply, because the LM317 has built-in shortcut protection.
short circuit lm317
If there is a need to significantly increase the power of such a Power Supply, then it is possible to use the LM338 or to connect one or two transistors in parallel to the LM317. More details about this can be found in the materials of the article “The Laboratory Power Supply 1.3-30V 0-5A – How to make?”.

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