The 7805 device is dissipating (wasting) 4 watts of energy to deliver 5 watts of energy to the circuit it is powering so efficiency is not very good but it may be fine for the application. The power dissipation of the 7805 device used to power that circuit is calculated as Power = (Vin - Vout) * Iout so in this case Power = (9V - 5V) * 1A = 4W. The circuit will consume 5V * 1A = 5W of power. As with a power resistor, the more voltage it needs to drop given the same amount of current, the more heat will be generated.Īs an example, let's say you are using a typical 7805 style linear regulator to drop 9V from a wall bug down to 5V to power a circuit that will draw about 1A of current. This is because the linear regulator uses a large power transistor which is throttled back in order to drop the voltage on the output and so it is basically acting like a large power resistor would to drop the voltage. The main one is that a linear regulator converts the higher input voltage down to a lower output voltage by dissipating the excess voltage as heat. They work well and are still widely used today but they do have some limitations.

A portion of that 5V may be further converted down to 3.3V to drive a lower voltage portion of the circuit.įor many years linear regulators where the standard for converting higher DC voltages to lower DC voltages. This might be something like converting the 12V from a battery down to 5V in order to power an electronic board. Converting a higher DC voltage to a lower one is a common requirement found in most electronic circuits.

Step down power converter