Why is the 555 timer doing this

173

02:07:22

I know that it is very glitchy, especially when its output is connected to a high capacitance or low resistance load, but how is it getting the numbers "-5V", and "-4V"? I think it should give -2V, and 2V, or possibly 2V, and 4V, since it has its own internal ground (as you can see if you look at the output pin giving 0V as the "low", instead of the realistic -6V).

published 8 years ago

rich11292000

8 years ago

In simulation, its perception is fixed with its internal ground. This reference sees +6 and -6. In reality there is no internal ground, the 555 can only perceive 12 volts, it doesn't know you split railed it 20 times or grounded it 20 times, the 555 just floats around ungrounded. Because the simulation puts the internal ground on the 555, we can only work with voltages positive to ground, a voltage negative to ground will produce reverse polarity. There is no functional operation to a reversed polarity 555, and no math.

hurz

8 years ago

That was one of the first things I published about 555 curiosities. This internal ground limits the use of 555, shit happens.

hurz

8 years ago

"555 internal ground issue" http://everycircuit.com/circuit/5048668184903680

jason9

8 years ago

Yes, but if that were so, wouldn't it have the peaks of the wave be at 2V and 4V? How is it getting the numbers "-5V" and "-4V"?

hurz

8 years ago

Its clear there is a zero voltage reference placed inside 555 and unfortunately not taken the GND pin to use as zero volt reference. How the internal model exactly looks like is the secret of EC developer. Who know's, and we can make as much reverse engineering as we like, but tomorrow maybe they change it ...

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.