i need a off delay timer circuit?

Question

i need a circuit to hold the input 5v dc for about 1 sec and then off. even if the input is not switched off.

is it possible with a 555 IC . pls give me the circuit diagram itself

Answer 1

Yes a 555 will do it, so will any monostable multivibrator (MSMV) IC of which there are many. How it's done depends on details you do not provide, but basically you feed the 5v from an OR-gate to your circuit. The inputs to the OR gate are the 5V supply and the Q output of the MSMV; also connect the supply through a resistor to the negative trigger of the MSMV. Now the when power supply goes off, but you have to maintain power to the MSMV which you may be able to do with a large capacitor. A lot depends on what the output is driving (how much current is needed) as to what actual circuitry you use. You could also build a circuit with a voltage regulator or zener diode driven by the 5V power through a resistor and with a capacitor across the input. The latter approach can be used if you are not critical as to the exact length of delay. If it is critical, use the MSMV method. If your power requirements are not large, this is easier done with CMOS components. There is a CMOS version of the 555 timer.

Answer 2

i strongly sugest getting a program called Crocodile Technology, download the demo, and they send you a serial key in the email, let me know when your done and how you like it