7805 voltage regulator circuit

// A 7805 voltage regulator: 9 V in, 5 V out.
//
// There is no microcontroller here. Press Run and the simulator solves the
// circuit; the number under the 7805 is its output.
//
// THE PINS. Looking at the front of the TO-220 with the legs down: IN, GND,
// OUT. The tab is GND too. The 7805 holds OUT 5 V above its GND leg whatever
// the input does, as long as the input is high enough.
//
// THE CAPACITORS. 0.33 uF from IN to ground and 0.1 uF from OUT to ground,
// close to the legs. They are on the datasheet because a regulator far
// from its battery or its filter capacitor can oscillate; they cost nothing,
// so they go on every build.
//
// THE DROPOUT. The 7805 needs about 2 V across itself to regulate. A fresh
// 9 V battery is 9.6 V, so the output reads 5.0 V. Drag the battery's charge
// down: at 50 % the battery is 7.2 V and the output still reads 5.0 V, and
// at 40 % (6.7 V) it just holds. Below that the output follows the input
// down: at 25 % the battery is 6.0 V and the output 4.3 V, and a flat
// battery's 4.8 V gives 3.2 V. That is why a 7805 wants 7 V or more in. An
// LDO such as the AMS1117-5.0 needs only about 1.1 V.
//
// THE HEAT. A linear regulator burns what it does not pass on: here the LED
// takes about 7 mA, so (9.6 - 5) V x 7 mA is about 30 mW in the regulator.
// At half an amp it would be 2.3 W, and the 7805 would need a heatsink.