Experiment 10 - The Low-Drop-Out Voltage Regulator LM2940

A typical Low-Drop-Out (LDO) voltage regulator is the LM2940. Its Drop-Out voltage is only 0.5 Volt.

In this experiment, you use the LM2940 with an output voltage V_out = 5 V. With a Drop-Out voltage V_DO = 0,5 V this means, that already at an input voltage V_in = 5,5 V the LM2940 provides a stable output voltage!

The LM2940 has the same assignment of the pins as the 78xx...

• Pin 1 is connected to the input voltage V_in.
• Pin 2 is connected to the zero potential (GND).
• Pin 3 is connected to the output voltage V_out.

Circuit diagram measurement of the voltage Vout of the LM2940.

Circuit measurement of the voltage Vout of the LM2940. (Enlarge)

For the voltage regulator to find its output voltage, the capacitor C1 needs to be included in the circuit. The capacity should in any case be larger than 22 μF.

But what about the heat generated by the LDO voltage regulator...?