Power conversionBench electronicsUnplug and unscrew
Linear regulator
Also called AMS1117, 7805, LM317, LDO.
A three-terminal regulator. 7805 (5 V, ~1 A, needs about 7 V in) and AMS1117-3.3 (SOT-223, dropout around a volt, needs capacitors close by) are the ones you can actually reuse. They turn excess voltage into heat.
If you are new to this category
These parts change wall power into the lower voltage a device uses. A sealed supply with a label is the safer kind. An open board from a lamp can still be connected to the wall on the side that looks like low voltage. Isolated means the output is not electrically connected to the wall. If you are not sure, treat the output as live.
Read the label out loud: volts, amps, and the polarity symbol. Then measure. A number you remember from a similar brick is not a measurement.
Left: a brick. The label is your spec, and the plastic is the safety barrier. Right: a board taken out of a lamp or a charger. Unless you have checked that the output is isolated from the prongs, do not let it touch a project you will handle while it is plugged in.
| What to look for | Usual figure |
|---|---|
| 7805 | TO-220, input, ground, output. Bypass caps required for stability in practice. |
| AMS1117-3.3 | SOT-223. The tab is Vout on the common clone, not ground. Confirm the datasheet of the brand you have, because tabs have surprised people. |
| Power | (Vin − Vout) × current must fit in the package and the copper. A 1117 at 1 A from 12 V is a mistake. |
Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.
What people actually use it for
- 5 V from a 9 or 12 V rail at low current
- 3.3 V from 5 V at low current
Leave this one when
The current is more than a few hundred milliamps and the drop is large. Use the original switcher instead.
Buying a new one is the better idea when
A small buck module, once you are above about a watt of dissipation.
How to tell if this one still works
Correct input, capacitors on, measure the output unloaded and with a small load.
Tools you will want: Meter, Capacitors.
Words on this page
Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.
- datasheet
- The manufacturer's document for a part: voltages, pin order, limits. A salvage part with no readable number does not have one you can trust.
Where people actually find it
1 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.
| From | Call | How many | How often | Where it sits |
|---|---|---|---|---|
| Router or modem | Bonus | 1 | usually | Near the SoC. |
- In this particular machine
- Often a 3.3 V SOT-223 regulator.
- Where to look
- Near the SoC.
- How to get it out
- Only if the marking is a part you recognize.
- The condition to expect
- Unknown otherwise.