Circuit that use to illuminate your cupboard or other such dark places have significant application because main connection is not possible in those areas. This circuit uses a simple battery to power the light and also built with a auto shut-off. This under cupboard lighting circuit will be a great alternative for traditional torches and also proves to be cost effective among all other lighting systems.
WORKING OF THE CIRCUIT:
The circuit is built around a single hex inverting buffer IC CD4049 which consists of six inverter gates in one package as shown in the below diagram. Two of these six inverters inside the IC( designated IC-1A and IC-1B) along with resistors (R2) and (R3) constitute the schmitt trigger. And rest of the inverters in the CD4049 IC are connected parallel together for lighting the lamp connected to the circuit.
Cd4049 Pin diagram
When the switch S1 is momentarily pressed the voltage across the capacitor rises to 6v almost instantaneously. The schmitt output goes HIGH which forces the output of four parallel connected inverters(IC:C to IC:F) go LOW thus switching ON the lamp. To sum up when the switch is pressed and released, the lamp lights up. Now the capacitor C1 has already started discharging through resistor R1 and the moment voltage across it decreases to a value that is treated as LOW state, the voltage at the point where four inverters are connected parallel becomes high thus switching off the lamp.
The Lamp in the above circuit will be ON for about two minutes with the given components before getting auto shut off. The time was given by the values of the resistor R1 and Capacitor C1 by the formula 1/4(R1 * C1). The inverters IC:C , D, E and F have been connected in parallel to increase the current sinking capability. Note that when the lamp is ON the lamp current would be flowing through the conducting output stages of these inverters inside the IC. And for a larger lamp current, a transistor switch should be used in place of parallel connected inverters.
