Here's a simple triac timer circuit which can be used for switching ON a particular device after a predetermined time, set through the given pot or the variable resistor.
The shown circuit diagram of a simple triac timer can be understood by referring to the following explanation:
How the Circuit Works
The left hand side section comprising the IC 4060 becomes the basic delay generator stage. As we all know, the IC 4060 is an extremely versatile time delay generator chip which has a built in oscillator for the required fundamental timing clocks.
The components connected at the pin#9,10 and 11 form the time delay determining parts of the IC.
Precisely, the resistor at pin#10 and the capacitor at pin#9 are responsible for fixing the delay period and may be adjusted for acquiring the required predetermined switching output.
This IC has 10 discrete outputs which produce delays or oscillation periods which are twice to the previous pinout in the order.
Here pin#3 produces the largest delay, followed by pin#2 and then pin#1 and so on as per the specified pinout order. So suppose pin#3 produces delay interval of 1 minute, then pin#2 would produce the same at an interval of 30 seconds, pin#1 at 15 seconds and so on.
Since pin#3 is specified with the highest time interval, we use this pinout as the output.
Therefore suppose we set the RC at pin#9 and 10 with a maximum delay of 2 hours, pin#3 would be assigned to generate alternately changing ON/OFF pulses, having equal delay intervals of 2 hours, meaning initially the output would be OFF for 2 hours, then ON for next 2 hours and so on as long as its powered.
The above explains the IC 4060 configuration, now let's learn about the triac configuration.
As we can see, the output pin#3 is directly connected to the gate of the triac, while the triac A1 and A2 are terminated with the load and the other specified parameters.
When power is first switched ON, C3 at pin#12 of the IC4060 makes sure that the timing count initiates right from zero by resetting pin#12 with a short pulse.
The output pin#3 now initiates with a logic zero output while the IC internal timer starts counting.
Due to the logic zero, the triac stays switched OFF initially along with the load.
Once the predetermined delay interval lapses, pin#3 instantly becomes high, triggering the triac and the load.
The diode connected across pin#3 and pin#11 plays an important function of latching the IC counting process.
If this diode is removed, the counting process will continue and after 2 hours the triac will be again become switched OFF, and this procedure will go on repeating every after 2 hours.
The diode shuts off this operation, and lathes the IC to the ON position permanently.
The above situation provides us with another interesting application of the proposed circuit, by removing the diode we can convert the above circuit into an AC lamp flasher circuit, the flashing rate being set by the RC components.
Also note that irrespective of the RC parts you have the option of selecting/connecting the remaining outputs of the IC with the triac gate for getting a diverse range of time delays.
Circuit Schematic for Delay ON Timer
The above triac controlled timer circuit becomes suitable for applications which requires a delay switch ON.
For applications which require a delay switch OFF meaning in cases where a load needs to be switched off after a predetermined time interval, the above circuit can be modified as given below:
Circuit Schematic for Delay OFF Timer
Parts list for the above simple triac timer circuit
R1 = 2M2
R3 = 100K
R2, R4, R6 = 1K
R5 = 1M
C1 = 1uF/25V (must be non-polar, use more in parallel for higher delays)
C3 = 0.1uF disc
C2 = 100uF/25V
C4 = 0.33uF/400V
Z1 = 15V 1watt zener
Tr1 = BT136
T1 = BC547
D1, D2 = 1N4007
P1 = 1M pot