Help with 555 simulation

131

03:04:58

Can someone please tell me why the simulation of the 555 isn't working? Is this a known issue, and if so is there a fix being developed? Or is the 555 still in beta testing? Is there a workaround?

Clearly the 555 should not cause 700 mA of current to the bulb when the battery in the circuit is only outputting 2 mA.

I have a more complex circuit that requires the 555, but because of this glitch it doesn't work at all in simulation.

published 9 years ago

WTFCircuit

9 years ago

You know, EC stuggle a bit with no sense simulations

psteichen

9 years ago

This is a simplified version intended to highlight the problem. It makes the same mistakes in more complicated applications.

jpoulin0901

9 years ago

Yeah, he's right, something is very wrong here. The voltage at pin 3 is an impossible -3V, making the voltage across the load read 12V. Although there's nothing wrong with connecting your load between pin 3 and Vcc in reality, the problem appears to be that with the 555 in EC, the load on pin 3 must be grounded. I work around it by putting a push-pull emitter follower pair immediately following pin 3.

psteichen

9 years ago

Hmm... I'm not familiar with a push pull emitter. I'll Google it, but if you have time could you explain it? Basically I need pin 3 to sync current, not be grounded. It works great on my bench...would love it to work in EC so that I can play with some modifications.

rich11292000

9 years ago

The 555 has a limitation of 200ma so obviously if you do more than that you won't get smoke like you do in reality. You get unrealistic results.

psteichen

9 years ago

Rich: Reduce the bulb to 4V and 500mW. This will bring the consumption down to less than 90mA. But it is still creating power out of thin air. Consumption of the battery will remain at 2mA. It's pretty clear that something is wrong with the 555 simulation.

2ctiby

9 years ago

could the lamp be the culprit rather than the 555 ... no problem with an LED

psteichen

9 years ago

2ctiby: I don't think so. Try replacing the bulb with a 30 Ohm resistor as a load. Same problem.

2ctiby

9 years ago

Right on thanks. Perhaps other alterable components need checking too. Meanwhile I'll take others advice here and expect nonsense results if I put nonsense there myself.

psteichen

9 years ago

Yeah I suppose. Unfortunately you can also expect nonsense with perfectly workable circuit designs. I have a time delay alarm that works perfectly on the bench. When entered in EC, not only does it do nothing timing wise, but the 555 creates a ghost current that powers the load (alarm) continuously. :(

Puscifer222

9 years ago

Often adjusting the "realtime"/circuit setting to start the animation can produce odd behaviors

psteichen

9 years ago

I'm not familiar with this setting. My settings page only has 3 options.

jpoulin0901

9 years ago

I kinda forgot about this.. I dont know how to link directly to a cct so I will explain what i meant. Take pin 3 to a resistor, then add an npn connected with collector at Vcc and a pnp with collector at ground. Connect both bases to the resistor and connect their emitters together. The buffered output is then taken from the the emitters. If you replace either transistor with a load resistor the resultant circuit is known as an emitter follower. I hope that clears things up.

avid0g

9 years ago

The software "bug" is due to the lamp simulator, more than the 555. This bulb acts like an enforced power consumer, ignoring external current limits and supply voltages. Trying a resistor instead works for me. Putting the bulb back in = FUBAR. Note the negative voltage at Output.

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