The LM7805 and AMS1117 are two of the most widely used linear regulators. They do the same job — turn a higher DC voltage into a steady lower one — but they suit different situations.
Side by side
| LM7805 | AMS1117 (3.3 V / 5 V) | |
|---|---|---|
| Output | 5 V fixed | 3.3 V, 5 V and other fixed versions |
| Output current | up to about 1 to 1.5 A | up to 1 A |
| Dropout voltage | about 2 V | about 1.1 to 1.3 V at full load |
| Maximum input | 35 V | 15 V |
| Common package | TO-220 (through-hole) | SOT-223 (surface mount) |
Dropout decides the minimum input
Dropout is how far the input must stay above the output for the regulator to work.
- An LM7805 needs roughly 7 V or more in to give 5 V out. It will not regulate from a 5 V or 6 V supply.
- An AMS1117-3.3 needs about 4.6 V in, so it runs comfortably from 5 V (USB). That is why it appears on so many development boards.
Heat is usually the real limit
A linear regulator burns off the unwanted voltage as heat:
Power = (Vin − Vout) × load current
Dropping 12 V to 5 V at 0.5 A dissipates (12 − 5) × 0.5 = 3.5 W. A TO-220 package without a heatsink rises by roughly 50 °C or more for every watt, so this needs a proper heatsink — or a different approach.
The same load from 7.5 V dissipates only 1.25 W. Keeping the input just above the dropout limit makes a large difference.
For SOT-223 parts like the AMS1117, the PCB copper is the heatsink. Give the tab a generous copper area, and keep dissipation to around a watt or less unless you have checked the thermal design.
Capacitors
- LM7805: the datasheet recommends 0.33 µF at the input and 0.1 µF at the output, placed close to the regulator.
- AMS1117: needs an output capacitor for stability — the datasheet specifies 22 µF tantalum. Leaving it out can cause oscillation. Check the datasheet of the exact part you buy before substituting a ceramic.
Which one?
- 9 V to 24 V supply, 5 V output, modest current: LM7805 with a heatsink sized for the dissipation.
- 5 V supply, 3.3 V logic: AMS1117-3.3.
- Large voltage drop at high current, or battery powered: use a switching (buck) regulator instead. A linear regulator would waste most of the energy as heat.
See what is in stock in Voltage Regulators, and pair them with the right capacitors.