CD4049 Based LED torch

A simple LED torch would light up 3 white LED from 6 volts supply in case of emergency or in darkness. It is qyite light-weight and handy, thus, can be used while traveling in train or in bus. Here we have used CD4049 IC which is a hex inverting buffer CMOS chip

CD4049 contains six inverter gates in one package as shown in diagram. In this, pin 3 is input and 2 is for output. For first gate similarly pin 5 is input and pin 4 is output for second gate similarly we have four more gates. Pin1 1 is for supply voltage and pin 8 is connected to ground. Pin 13 and 16 are unused.

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Fig. 1: Circuit Diagram For Voltage Doubler Circuit Using IC 4049

This LED torch circuit is based on NOT gate CD4049 IC and utilizing 3 gates of NOT gate IC. To understand the working you should know about the truth table of NOT gate which is:

Input	Output
0	1
1	0

In NOT gate, we will get output as logic high when logic zero is provided and we will get logic zero when logic1 is provided in input.

To understand the working of a circuit switch on the power supply. You can see in the figure that pin 7 of IC1 is connected to ground hence we will receive a logic high at out pin of gate 3 or at pin 6. This high is supplied to input pin of gate 2 and we will receive a low at pin 4. This is again supplied to input pin 3 of gate 1 and as a result we will receive high or +6V at out pin 2 which, in turn lights up the LED.

Here we have connected the resistor and a capacitor at the pin 7 for the process of amplification of signal. And we have connected the LED in series to save the life of the battery. Let’s say a single LED will require 20mA of current at 3.8 Volts to illuminate brightly; therefore, if we connect 3 white LED’s in parallel, they will require current consumption of 60mA. As it draws more current, battery connected to the circuit will die out soon therefore it is good practice to connect LED in series.