78xx Fixed Linear Voltage Regulators
The 78xx family is the classic family of fixed positive linear voltage regulators. The last two digits traditionally indicate the nominal output voltage: 7805 for 5 V, 7812 for 12 V, and 7815 for 15 V are familiar examples.
REGULATOR→regulated DC
What is inside the three-terminal package?
The regulator contains a voltage reference, an error amplifier, a pass transistor, and protection circuitry. It continuously adjusts the pass device so the output stays near the intended voltage while the input voltage or load changes within the device's allowed operating range.
Common fixed values
| Example | Nominal output | Typical use |
|---|---|---|
| 7805 | +5 V | Classic logic, controllers, instrumentation, small regulated supplies. |
| 7812 | +12 V | Analog circuits, relays, audio and control circuits. |
| 7815 | +15 V | Traditional analog and op-amp supplies. |
The related 79xx family provides fixed negative output voltages. Positive and negative regulators are often paired in dual-rail analog supplies.
The extra voltage becomes heat
For example, dropping 12 V to 5 V at 0.5 A means the regulator must dispose of roughly 3.5 W as heat. That is why package type, heat sinking, ambient temperature, and thermal limits matter.
Capacitors and layout
Small bypass capacitors are commonly placed close to the regulator input and output. Exact recommendations depend on the device and layout, so use the manufacturer's datasheet rather than assuming every 78xx-compatible device has identical requirements.
Manufacturer reference: TI LM340 / LM7805 family.