555 timer does not return to Ground state

[alagiri]

which relay diode to use with a 555 timer

I needed a DC motor to be running for particular duration. I wired a 555timer. The 555 was made to power a relay so that the relay would make/break the power to motor.

I observed that the moment the timer is triggered, the 555 goes to ON state but doesn't return back to low state even after the RC duration. Can somebody suggest why this happens?

 

[matbob]

Could you please post the circuit?

 

[viperpaki007]

It can probably be due to the inductance of the relay coil...inductor will cause the current to keep on flowing even after the 555 has given zero logic at it output...so i think the best way is to use a transistor instead

 

[davidgrm]

Use a transistor. Also put a diode in reverse across your relays coil. Put a 100u capacitor across the 555 supply line

 

[randell_xtian]

you can try the suggestion by davidgrm. it will work.

best regards,
randell_xtian

 

[viperpaki007]

Davidgrm suggesstion will work but you can also use a power transitor (depending on motor rating) in darlington configuration as a fast swicth.
I think TIP121 will be good if you dont have much biggger motor.

 

[nagender]

i think u have connected the discharge pin to relay,in relay inductor will be there, it stores some energy so even though the 555timer is in off position you are not able to observe it plz try it by connecting the discharge pin any other i mean resistor and capacitor