555 timmer circuit issue!

[sherazi]

hi all!

i wanted to use a 555 circuit for flashing 24V bulb, i had desined the circuit! for 12V first and it works fine , now i added a bridge diode rectifier and a zener to alter my input source to be 24Vac , after rectification and using a 12v zener the circuit doesnt flash , its On all the time ! plz can you check the schematics

in the working circuit taht uses 12Vdc there is no zener , now i added the zener as shown and the ac 24 v are rectified before that !

 

[kak111]

I drow a simple circuit for you.

View attachment 12V_to_555_circ.pdf

Regards KAK

 

[vinoth8051]

Hi sherazi,
1) Diode 1N4001 is not zener diode, Replace with the suitable one
2) Resistor in series with zener diode is necessay.

 

[Syncopator]

now i added the zener as shown

The only diode in your diagram is an ordinary diode, not a zener. It does nothing.

Do what Kak suggests.

 

[sherazi]

The only diode in your diagram is an ordinary diode, not a zener. It does nothing.

thats by mistake in the schematic ! its actually a 12v Zener diode!

 

[kabiru]

You can also use 7812 regulator and use 2.2k resistor as pull down from pin 3 of your 555 to ground.

 

[sherazi]

......and use 2.2k resistor as pull down from pin 3 of your 555 to ground.

can u explain the reason for this?

 

[kapilp]

try separating the rectifier and 555 section. Power up the same 555 section with some other 12V supply and then check whether your rectifier (without 555) gives you 12V. One of the two should give a problem .... this should simplify things ...

 

[kabiru]

7812 is a 12v regulator is give you regulated 12v even if the supply is more than 12v then the 2.2k resistor is used as pull down to make sure that the output of your 555 is pull to ground except it change it's state from low to hi or vise-vasa.

 

[Syncopator]

... the 2.2k resistor is used as pull down to make sure that the output of your 555 is pull to ground except it change it's state from low to hi or vise-vasa.

It isn't necessary.

The 555's output had both active pull up and active pull down.

 

[kabiru]

When the 555 expirience a noice from the power supply it toogle the output.

 

[Syncopator]

When the 555 expirience a noice from the power supply it toogle the output.

That can be eliminated with proper supply decoupling.

 

[kabiru]

yes of course with a proper filtering of ripples it will be okey.