Accurate threshold voltage for mosfet

[Dknot--]

Hello everyone,

I have N mosfets, which, according to datasheet have Threshold voltage between 1 and 2 volts. So, unfortunately I do not know excatly voltage when those transistors are passing current and when not. I would still need that information.
When Mosfet's datasheet explains threshold voltage to be in 1-2 volts, I assume that means between 1-2 volts Mosfet is partially ON, and this depends on currents that transistor is handling?
Is there any Mosfet available with very accurate threshold voltage, so there would be no "linear region" ? So, it would be either OFF or ON.

Also, is there also some easy way to measure drain current/drain to source voltage for certain Mosfet.

Thanks already for your answers and follow up questions,

-DKnot--

 

[MikeMl]

No. All Mosfets require a Gate to Source voltage several times Vt to turn them on hard enough to get the specified ON Resistance from Drain to Source.

If you want a small, predictable ΔV to turn On/Off a Mosfet (where dissipation in the FET must be minimized), use an active gate driver circuit which ultimately applies 0V and 10V Vgs (0V and 5V for a Logic-level Mosfet). Ideally, such a gate driver will have a Schmitt-trigger switching action.

 

[Dknot--]

Thanks Mike,

I have quite predictable ON/OFF-voltages. Boundary would be, let's say 1,5 volts, and no hysteresis needed. I'll start to check right kind of Mosfet gate driver-components.

If anyone has some mosfet gate driver component in mind, I would apprechiate suggestions,

BR,

-Dknot--

 

[ronv]

You can drive most of them with digital logic. The trick is to have the gate voltage pass through the threshold quickly to minimize power dissipation in the mos fet. A good driver would have a rise time less than 100 ns a bad one over a microsecond or two. The driver must also overcome the gate capacitance so good ones will have high current drive capability to keep the time constant of the turn on/off signal short. Most also like about 10 volts between gate and source to fully turn them on and you will see these figures in the data sheets. You can usually calculate drain to source current by knowing the resistance of the load and the resistance of the fet in the on state. Drain to source voltage is the voltage across the device when it is off.

 

[nickelflippr]

If looking for some mosfets with a guaranteed Rdson at low voltages, then browse Farichilds Portable Solutions brochure.

 

[audioguru]

The Mosfet is almost completely turned OFF when the gate voltage is at the threshold voltage (0.00025A). Don't you ever want the Mosfet to turn ON?

 

[CafeLogic]

Get a FET characterized at 4.5V and drive it with a comparator. Then, you can set the threshold voltage to whatever you want it to be. If you want decent switching times, make sure to get a "push-pull" comparator and not an open-drain model.