Common Failures of Regulators

Burning smell? It might be your regulator.

The 1.5A TO-220 packages require a heatsink and ventilation to operate at full capacity. Otherwise they will get hot. When semiconductors get hot, the resistance of their tracks and junctions increases, then they get hotter, and a condition known as 'thermal runaway' occurs. The heat generated is a combination of the size of the voltage drop (i.e. Vin - Vout) and the output current. If either or both are large, a heatsink is a good idea. Many regulators come with an internal thermal cutout switch, which clicks off if it gets to hot. This protects the regulator and the circuit it supplies, but it counts as a malfunction.

The most common way to kill a regulator is by short circuiting the output to ground (generally due to a fault / solder bridge in the load circuit), or by inserting it backwards (i.e. pumping power into the output...). Before powering on for the first time, it pays to do the usual visual checks of any soldered board, and also use a multimeter to determine the resistance between the output and ground. A short will be a big obvious '0' (or thereabouts). Be confident you know which pin is which, and you have them connected correctly.