Experiment 11 - The Delay Circuit
A machine that turns itself on only after a delay?
In some situations this may be an advantage.
In such an application capacitors are used.
Find out how here.
Consider the circuit shown.
In the circuit diagram you see the capacitor C1 in combination
with the resistor R1.
Circuit diagram of a delay circuit.
This is called a delay circuit.
When closing the switch S1,
the light-emitting diode LED1
lights up with a delay of afew seconds.
And this is going on in the circuit...
Closing the switch S1,
the total current flowing through the resistor R1
also flows as a charging current through the capacitor C1.
This basically short circuits the base and the emitter of the transistor
and the transistor is shut.
The LED remains dark.
If the capacitor C1 is fully charged,
the charging current dries up
and the capacitor becomes an insulator.
The total current through the resistor R1
now flows to the base of the transistor
and the LED lights up.
From the last experiments it is also clear that a capacitor
with a higher capacity results in a longer delay.
But not only the capacitor determines the behavior of the circuit,
as you can see easily in the following experiment...