Voltage regulators are an essential part of many projects that require a stable input voltage. Their job is to take an unregulated input voltage and output a regulated voltage, with the only catch being that the input voltage must be higher than the output voltage. If you’ve got a project in the works that needs a specific voltage, here are several options you may consider:
Fixed Voltage – LM78XX
The LM78XX series of linear voltage regulator chips are extremely popular, and for good reason. They’re cheap, easy to use, require few other components, and have built-in circuit protection against drawing too much current. There are different models for outputting different voltages, and the last two numbers in the model number denote their voltage output. For example, the LM7805 outputs 5 volts, the LM7810 outputs 10 volts, and the LM7824 outputs 24 volts.
Fixed Voltage – Zener Diode
You’re halfway through your project, and you just realized you’re fresh out of linear regulator ICs. What can you do? If you’ve got the right voltage zener diode and a power transistor, you can make your own fixed voltage regulator using the circuit diagram above. The output voltage will be 0.6 volts below the diode’s zener voltage, due to the base-emitter voltage drop across the transistor.
Variable Voltage – LM317
When you need to be able to adjust the voltage output of a voltage regulator, the LM317 is right for you. It is very similar to the LM78XX series, except that it has an adjustment pin to change the voltage output. By adding a potentiometer to your circuit, you can use it for purposes like controlling fan speeds or variable voltage power supplies.
A Note on Heat Sinks
The larger the voltage drop across the voltage regulator, the more heat will be dissipated through the component. In order to keep it from burning up, make sure to use a heat sink!