A Linear Voltage Regulator ensures the output voltage from the circuit is maintained at a specific voltage. The device acts as a variable resistor, continuously adjusting to maintain a constant output voltage. The regulated voltage must be lower than the input voltage. Simple voltage regulator contains a Zener Diode and a resistor but more complicated versions include elements like a voltage reference and error amplifiers.A more specific type of regulator are Low Dropout Voltage Regulators (LDO) which can regulate voltage even when the power supply voltage is very close to the supply voltage.How to choose linear voltage regulator ICs?The primary feature in choosing a regulator is usually the Output voltage as the main purpose of one is to regulate the voltage to a specific value such as 3.3V. Its accuracy to this voltage across temperature and load current is another consideration as is its maximum load. The dropout voltage value will be particularly important with battery applications.How to test a linear voltage regulator?Set your multimeter to the voltage settingCheck the datasheet to determine which pins are the ground, input and output.Attach the red wire to the input and the black wire to the ground, the multimeter should give a reading higher than the regulators’ output value. If not then there is a power supply issue.Attach the red to the ground and the black wire the output, the multimeter should then give the regulators’ output value (plus minus its accuracy). If not then the regulator is likely to be faulty.