Experiment 1 - The Voltage Regulator

How do you connect the 78xx? Here you get to know a simple circuit using a 7805...

Consider the circuit shown...

• Pin 1 (V_in) is connected to the positive pole of the battery.
• Pin 2 (GND) is connected to the negative pole (zero potential) of the battery.
• At Pin 3 (V_out) a voltage of 5.0 Volt is present.

The light emitting diode LED1 lights up. In order to limit the current through LED1 to 20 mA, you use a resistor of 150 Ω....

Circuit diagram voltage regulation with the 7805.

Circuit voltage regulation with the 7805. (Enlarge)

With a multimeter you can easily convince yourself that the voltage V_out = 5 Volt...

Circuit diagram measurement of the voltage Vout of the 7805.

Circuit measurement of the voltage Vout of the 7805. (Enlarge)

The tolerance of a typical 7805 is 4% (see the datasheet). The voltage V_out can therefore differ by 0.2 Volt up or down.

But what happens to the voltage regulator at a higher input voltage V_in or under load...?