Mosfet question re Gate Voltage

Thread Starter

Hoylegj

Joined Mar 10, 2016
26
Hi,

I'm using a IRFZ44N in a Pic controlled motor on / off circuit which seems to works. I have 2.9 volts on the Gate Pin and 12 volts driving the Motor.

But I don't fully understand the datasheet. Would you be able to help me and confirm if I'm understanding it correctly.

The datasheet appears to be saying, the gate has to be between 2 and 4 volts above the source voltage.
And given that source voltage is normally 0v it has to be between 2&4 volts.

The Data Sheet Says :-
Vgs Gate-to-source Voltage +-20
Vgs(th) 2.0 - 4.0 V

Many thanks

Geoff
 

LesJones

Joined Jan 8, 2017
4,174
The gate threashold voltage is the voltage when the MOSFET JUST STARTS to conduct (250 uA drain to source current) Wit 2.9 volts on the gate it MIGHT have started conducting but some samples of the device might only start conducting with 4 volts on the gate. So if you only need 250 uA to drive you load the 4 volts will be enough. It is more likely that wou will need more current so I would aim to drive the gate with 10 volts. The Vgs rating of 20 volts is the maximum rating.

Les.
 

Thread Starter

Hoylegj

Joined Mar 10, 2016
26
The gate threashold voltage is the voltage when the MOSFET JUST STARTS to conduct (250 uA drain to source current) Wit 2.9 volts on the gate it MIGHT have started conducting but some samples of the device might only start conducting with 4 volts on the gate. So if you only need 250 uA to drive you load the 4 volts will be enough. It is more likely that wou will need more current so I would aim to drive the gate with 10 volts. The Vgs rating of 20 volts is the maximum rating.

Les.
I see, that makes more sense, thanks Les.
 

Bordodynov

Joined May 20, 2015
3,177
The datasheet specifies the range of the threshold voltage. With this (threshold) voltage, the current of the transistor can be equal to 250 μA. Check the amount of current from the datasheet. For normal operation of the transistor, the gate voltage must exceed the threshold voltage by several volts. For a given transistor, this voltage should be 7-10V. Those. It is not good for you. Look for a logic-level transistor with a threshold of 0.5-1.5V. Alternatively, use an additional transistor to amplify your 2.9V to 12V.
 

Thread Starter

Hoylegj

Joined Mar 10, 2016
26
The datasheet specifies the range of the threshold voltage. With this (threshold) voltage, the current of the transistor can be equal to 250 μA. Check the amount of current from the datasheet. For normal operation of the transistor, the gate voltage must exceed the threshold voltage by several volts. For a given transistor, this voltage should be 7-10V. Those. It is not good for you. Look for a logic-level transistor with a threshold of 0.5-1.5V. Alternatively, use an additional transistor to amplify your 2.9V to 12V.
Good Point, thanks, have a bunch of general transistors, so that's the way forward.

Many thanks
 

shortbus

Joined Sep 30, 2009
10,045
@ Hoylegj, what is the truck in your Avatar if you don't mind? Could you post it full size in the thread? The thumbnail picture is hard to make out. I've got a stalled project of a 1937 Ford truck that I need to get back to working on. In the process of building the frame, and life got in the way, hoping to work on it this summer.
 

Thread Starter

Hoylegj

Joined Mar 10, 2016
26
@ Hoylegj, what is the truck in your Avatar if you don't mind? Could you post it full size in the thread? The thumbnail picture is hard to make out. I've got a stalled project of a 1937 Ford truck that I need to get back to working on. In the process of building the frame, and life got in the way, hoping to work on it this summer.
Hi, truck looks fun, and I know the life problem.. mine is a 1959 for Popular, the project has been running almost 3 years now, this is my build thread with various pictures.
rodsnsods.co.uk/forum/garage/my-59-pop-build-140817
 
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