Author Topic: Positive, Negative and Ground via single pin  (Read 1229 times)

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Offline kiran_shresthaTopic starter

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Positive, Negative and Ground via single pin
« on: April 01, 2020, 05:47:04 am »
Hey everyone. I have been designing circuits for years but I never thought this could be a problem for me.
This time I came up with a problem. I need to design a small circuit based on mosfet or OPAMP which can switch between 0 , +V and -V from single output pin with control signal.
I can't use relays or multiplexers, I need a OPAMP or MOSFET design idea. If someone have idea please let me know.
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Offline KaneTW

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Re: Positive, Negative and Ground via single pin
« Reply #1 on: April 01, 2020, 07:04:35 am »
Any R2R opamp could do it with binary inputs on inverting and noninverting. Kinda overkill though.

For MOSFETs, just do a halfbridge but with a third MOSFET for V- IMO.
 

Offline kiran_shresthaTopic starter

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Re: Positive, Negative and Ground via single pin
« Reply #2 on: April 01, 2020, 07:10:15 am »
Yes, thank you for it. The op amp solution i not good for me but i think the mosfet circuit would work for me. I will give it a try.
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Offline Mechatrommer

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Re: Positive, Negative and Ground via single pin
« Reply #3 on: April 01, 2020, 07:34:38 pm »
I need to design a small circuit based on mosfet or OPAMP which can switch between 0 , +V and -V from single output pin with control signal.
I can't use relays or multiplexers, I need a OPAMP or MOSFET design idea. If someone have idea please let me know.
what exactly is the specification? what power rails available? whats magnitude +V and -V we are talking about? what control signal level and speed? what is the single output? and what its driving? if you ask for people's time, you should give more details. better with diagram or existing circuit/schematics.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline kiran_shresthaTopic starter

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Re: Positive, Negative and Ground via single pin
« Reply #4 on: April 02, 2020, 04:45:24 am »
Thanks for reply Mr Mechatrommer but I just required a logic not a final schematic.
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Offline ajb

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Re: Positive, Negative and Ground via single pin
« Reply #5 on: April 02, 2020, 05:59:54 am »
Start with a digital output that can be tristated (set to high impedance). Use a resistor divider to pull the output to the middle of the rails when tristated. You now have a node that can be set to 0V, your logic voltage (call it VD), or halfway between 0V and VD.

Now you just need an op amp circuit to offset and amplify that range to V+, V-, and 0V. 

If VD = V+, then this is very simple: use a non-inverting amplifier with a gain of 2 (both resistors are equal), use the above tri-level output as the input, and connect the reference node of the amplifier (usually ground) to V+. So an input of 0V gives V-, V+/2 gives 0V, and V+ gives V+. The whole thing can be done with one op amp and four identical resistors.

If VD != V+ you'll need to adjust the gain and reference voltage to get the right behavior.
 

Offline kiran_shresthaTopic starter

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Re: Positive, Negative and Ground via single pin
« Reply #6 on: April 06, 2020, 09:00:58 am »
Thank you very much. This is what I am looking for.
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Offline Zero999

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