My SPICE program is telling me that even when I remove the GND supply from a 556, the 556 still outputs normally, whats going on?

When the transistor is *ON* the 556 will get power ! You need to turn it off. I'm doubtful this is a great configuration to turn off power though. Where do the related Rs and Cs connect to 'ground' ? At the transistor collector or the power supply 0V ?

Graham

some models internally connect to gnd (node 0)

Colin =^.^=

Thanks for answering, i meant when I turn the transistor off. I had a suggestion from some other people to use the Rs, reset pin, instead of the ground, because of internal groun connections, etc. However I am having a hard time realizing how to use a transistor to control the Rs pin. I could use an inverter connected to a PNP, but i am looking for something more simpler.

Hmmm. How much amperage does the reset pin need? does it just need a logic level signal? if it does, than I guess I could just directly connect it to my digital circuitry.

the

I didn't mean the reset specifically. I meant all the resistors and capacitors needed to make it function that normally go to ground. They would have to be connected to the npn transistor's collector along with V- on the 556.

There's no reason you can't switch power to V+ with an npn emitter follower though.

Graham

In general, many/most spice models do not model power supply effects by design. Unless a model specifically says what supply effects it includes, assume it don't.

Kevin Aylward snipped-for-privacy@anasoft.co.uk

SuperSpice, a very affordable Mixed-Mode Windows Simulator with Schematic Capture, Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers on their knees, with their eyes closed"

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though.

Well, yes, there are several, albeit not why you "can't", but why you _shouldn't_.

But they're not as bad, or as numerous, as the reasons why you shouldn't open the ground pin. J D's idea of the reset pin is ideal. J D, drive the reset pin with any logic output (except maybe ECL ;-) ) and that will make the 556 (at least the sectiou whose reset pin you're manipulating) stop.

You do have to account for the stretched first half-cycle after you release reset, of course.

Good Luck! Rich

With all the free pic web sites out there, why not post a schematic.

Then everyone will know exactly what you are trying to convey.

A pic is worth a thousand 'i meant'S.

You could try making your own model, of course you would have to be carefull if you used comparators or flip flops that they dont also use GND internally.

maybe just copy the 555 transistor level model from the data sheet ?

Colin =^.^=