555 timer with negative power supply

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kev241

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555 timer power supply

Hi I hope someone can assist me with a small design question regarding a 555 timer IC.

Can a 555 ic be operated using a negative power supply? with the the usual positive voltage connected to ground?

I was given a circuit to power a 555 ic using a -5v connected to pin 1 and 6 with pin 4 and 8 grounded and am uncertain how this is supposed to work from looking at the datasheet of the 555 timer.

The 555 is used in atstable mode to pulse light source at 9.25 Hz with a 50% duty cycle. It is similar circuit to the one on thread by k7elp60.

Here is the circuit:
This was a working circuit and i didnt question it till it stopped working.
 

555 timer negative supply

It doesn’t make any difference which pole you label with (0)V ..
That is the matter of convenience and/or convention ..
For as long as the 555 “sees” the right polarity your circuit should work just fine ..

Rgds,
IanP
 

555 negatine

Hi ian P.
Thanks for the reply. So the circuit attached should work fine with the capacitor connected to negative 5 v and pin 8 and 4 to GND and pin 1 at the lowest potential ie -5v.
Just want to be sure as im a bit of a novice at this.
Thanks again.
 

Hi, Kev. I suppose this is not an issue in your low frequency application here, but it's recommended to add a capacitor of 10nF across pin 5 and negative supply - pin 1. I always put it there, it's just one component after all.
John
 

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    kev241

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HI JC,
Thanks for that. I added the capacitor since from seeing it on another forum but thanks for the tip. Board is all working fine again. 555 timer was broken along with a couple of other components, built a tester and this showed it was faulty.
Thanks for the help.
case closed
Kev241.
 

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