Hi,

I'm trying to figure out how to design a circuit that can execute action#1 when it detect above 2.5V and action#2 when it detect below 2.5V.
I'm looking at using NPN and PNP mosfet.
The source that i have is 2.8V and 2V. What i want to do is when 2.8V, it will trigger a solid state switch and when 2V, it will trigger another solid state switch.
Any idea?

 

hi Ivan,
Welcome to AAC.
The usual way is to use a comparator IC say a LM393 or similar type.
E

 

The MOSFET can't do the job for you, if you need to have a accurates detection then you should use the comparator as Eric suggested, or you want to try the bjt to do the detecting job as below, the R1 and R4 will be limited the Ic current and detection voltage.

 

Use a dual comparator and use hysteresis on both of them.

http://www.ti.com/lit/ug/tidu020a/tidu020a.pdf

Regards, Dana.

 

See

 

Another possible approach -



Note the Vz too high in this example, its the lowest the tool had.
You can get down to 1V Vz. Pick Vz = Vtrip - ~.7V

A higher beta transistor will have sharper trip curve.

Regards, Dana.

 

thanks guys, the comparator seems like the way to go. Next i need to make sure the circuitry is working, and all the component that i am using is kinda tiny for a breadboard. What would be your advise? Do i need to validate it on a breadboard or simulation is sufficient? If with simulation, what type of simulator is good for validation of the circuitry?

 

The library and components models of LTspice free download.

 

To handle small parts in proto consider using adapter boards. Go to
ebay.com and search for "soic adapter board", lots of offerings.

Sim of circuit should suffice, LTC Spice more than adequate. Or Tina TI Spice.

Look at datasheet for parts to make sure you are meeting common mode input
range limitations, same for output levels. You have not mentioned speed or
rate of incoming signal concerns, those also need to be evaluated for part you
choose.

Regards, Dana.