How to Test 78L05 Voltage Regulator

A voltage regulator is a component that maintains a fixed amount of output voltage regardless of the input voltage. You can find voltage regulators in the power supplies of computers and other electronic devices. Whenever DC voltage stabilization is required, a voltage regulator is likely going to be used to perform that action.

The 78L05 voltage regulator is one specific type of voltage regulator. The “78” number identifies it as a positive voltage regulator, while the “05” signifies the output voltage is 5 volts. It is a three-terminal voltage regulator, which includes the input terminal, ground terminal, and output terminal.


A voltage regulator test will determine the amount of voltage going into the voltage regulator and the amount of voltage going out of the regulator (input and output). You will need a multimeter to conduct a measurement of the input voltage and output voltage. It is an electronic measuring instrument designed to measure resistance, voltage, and current.

When you’re ready to perform the test, you can start by testing the input voltage. Switch the setting on the multimeter to “DC voltage.” It should have a “V” symbol or something similar. You’ll see the multimeter has a positive probe and a negative probe. Attach the positive probe to the input pin on the bottom of the voltage regulator. Then attach its negative probe to the ground pin.

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The multimeter has a digital screen that will indicate the amount of voltage. The input voltage should be higher than the output voltage by about 1 to 2 volts. You can find out by performing a similar measurement of the output voltage. All you need to do is take the positive probe off the input pin and place it on the output pin. You can leave the negative probe on the ground pin.

The amount of output voltage indicated should be 5 volts because of the “05” associated with 78L05. If you see a different number other than 5, then your voltage regulator is defective.