Battery Voltage LED

In many small battery powered apparatus it is common to have an LED act as a combined indicator for ‘power-on’ and ‘battery state’. The most commonly seen circuit fir this is shown in Figure 1. Although it is assumed that a 78L05 is used in all circuits to be discussed, the concepts can be extended to other (low-drop) voltage regulators as well.The 78L05 requires a minimum input voltage of 6.5 V to work properly. In Figure 1, the LED voltage will be about 1.8 V, with the zener diode dropping 4.7 V and the resistor, the excess voltage above 6.5 V.