Electronics > Beginners

MOSFETS as voltage controlled gates

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SolderOcelot:
I need 3 gates in my circuit which each should close (as in: let current go through source and drain) IF the circuit voltage is > X.
 
My question: Are MOSFETS the right tool for this construction?

My goal is to create a LED strip that lights up a number of LEDS depending on voltage. Please take a look at attachment for schematic.

ArthurDent:
Here is an IC that is designed for this type of application and I'm sure there are some others.

https://www.ti.com/lit/ds/symlink/lm3914.pdf

SolderOcelot:

--- Quote from: ArthurDent on November 18, 2018, 12:34:37 am ---Here is an IC that is designed for this type of application and I'm sure there are some others.

https://www.ti.com/lit/ds/symlink/lm3914.pdf

--- End quote ---
On one hand I think it's pretty cool that IC's come onto my path now but on the other hand it's quite a buzzkill to just slap an iC on there and be done with the project. I was hoping to build this a bit more primitively.

Whales:
You could use varying amounts of diodes in series to each LED.  The turn-on might not be as abrupt as you hope, however.

Another alternative is to use diode stacks that then feed the base of an NPN.  That might have a sharper turn-on.  I suspect FETs would again be too gradual of a turn on.

SolderOcelot:

--- Quote from: Whales on November 18, 2018, 01:33:50 am ---You could use varying amounts of diodes in series to each LED.  The turn-on might not be as abrupt as you hope, however.

--- End quote ---
What do you mean with "abrupt"? As in speed in which LEDs switch on or the contrast between the LEDs' on and off state (diffusion).


--- Quote from: Whales on November 18, 2018, 01:33:50 am ---Another alternative is to use diode stacks that then feed the base of an NPN.  That might have a sharper turn-on.  I suspect FETs would again be too gradual of a turn on.

--- End quote ---
So with "diode stacks" the diodes act as voltage barriers right? So the first stack would require a voltage of 1.3 for current to go through right? If so, I'm worried about the amount of resistence they add to the circuit which would interfere with other features.

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