- The regulator uses the difference between an unregulated source and the controlled value of the regulator's output. A 5-volt regulator won't work with a 3-volt input, but it works well with 6 or 7 volts. Engineers call the difference between input and output the dropout voltage. You should keep this difference small or the regulator will become hot.
Ohm's Law for Power
- You can calculate the heat energy a regulator produces by using Ohm's Law for power, multiplying the dropout voltage by the regulator's current. If a regulator provides 1 amp of current, a 5-volt output and a 6-volt input, the 1-volt dropout difference times 1 amp equals 1 watt of heat.
- Many voltage regulators, such as the popular LM317 and 7800 series 3-terminal types, have a feature that shuts the regulator down if it gets too hot. This prevents the regulator from destroying itself from excess heat.