Circuits / Power
7805 regulator with a pilot LED
A fixed output from a higher input; the difference is lost as heat in U1
Tap a part to see its voltages and currents. It is a model, not a measurement.
What do you need?
- Capacitor 330 nFSearch on Amazon
- Voltage regulator 7805Search on Amazon
- Capacitor 100 nFSearch on Amazon
- Red LEDSearch on Amazon
- Resistor 1 kΩSearch on Amazon
- Jumper wires × 5Search on Amazon
- BreadboardSearch on Amazon
How does a 7805 voltage regulator work?
A 7805 is a linear regulator: it takes a higher, rougher voltage at its input and gives a steady 5 V at its output, whatever the load draws, within its limits. Here it turns 9 V into 5.00 V, which lights the pilot LED through R1 (1 kΩ) at about 3.4 mA. It does this by acting as a variable resistor that takes the difference: 4 V times the current flowing. At 3.4 mA that is about 13 mW of heat, nothing; at 1 A it would be 4 W, enough to need a heatsink. That waste is the main limit of a linear regulator. The 7805 also needs about 2 V more at the input than it gives, so 7 V is about the lowest supply that works. C1 (330 nF) and C2 (100 nF) are the capacitors its datasheet asks for, close to the pins, to keep it stable.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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