Power & protection

Voltage regulator

Turns a higher or wobbly voltage into a steady lower one, such as 12 V into 3.3 V. A linear regulator (LDO) burns the difference as heat; a switching (buck) regulator chops it up with an inductor and wastes very little.

Think of it as: A pressure-reducing valve on a water main: high, varying pressure in, steady lower pressure out.

Pins

IN: : The higher input voltage.
OUT: : The regulated output. Needs the output capacitor from the datasheet to stay stable.
GND: : Common ground. Buck regulators also have pins for their inductor (SW) and often a feedback pin (FB).

Linear regulators are simple 3-pin parts (7805, AMS1117). Buck converters are small chips plus an inductor, diode and capacitors, often sold as a ready-made module. Pin orders differ between parts.

What to look for inside

Inside a linear regulator: its pass transistor acts like a resistor that adjusts itself to drop 7 V down to 3.3 V, while the load current rises and falls.
All of the current flows through it, and the extra 3.7 V is lost across it. So the heat is (U_in − U_out) × I.
At 0.4 A that is about 1.5 W of heat for 1.3 W of useful output. This is why buck converters exist (lesson 5.1 shows both side by side).

The numbers that matter

Spec	Typical
Output voltage Fixed parts have it in the name: AMS1117-3.3.	1.8 V · 3.3 V · 5 V or adjustable
Dropout voltage The input must stay at least this much above the output, or it stops regulating.	0.1 V to 2 V (linear)
Max output current For a linear part, heat usually limits you long before this.	100 mA to 3 A
Quiescent current What it uses itself. Matters for battery-powered projects.	1 µA to 5 mA

Where you’ll use it

Powering a 3.3 V microcontroller from USB (5 V) or a battery.
A clean, quiet supply for sensors and analogue circuits (linear).
Efficient power from 12 V or 24 V rails (buck).

Common mistakes

Using a linear regulator for a big drop at high current. 12 V → 3.3 V at 0.5 A is 4.4 W of heat: far too hot for a small part.
Leaving out the input and output capacitors. The regulator can oscillate.
Forgetting dropout: a 3.3 V LDO with 1 V dropout cannot run from a 3.7 V battery.

Lessons that use it

Go deeper

P_{LDO} = (U_{in} - U_{out})\,I_{load},\quad \eta = \tfrac{U_{out}}{U_{in}}

Linear: heat and efficiency.

D = \tfrac{U_{out}}{U_{in}},\quad \Delta I_L = \tfrac{(U_{in} - U_{out})\,D}{L\,f_{sw}}

Buck: the switch is on for a fraction D of each cycle; the inductor smooths the current.

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