FET for controlling current up to 6A (urgent)

Thread Starter

mahela007

Joined Jul 25, 2008
45
Can you suggest a JFET or MOSFET that is capable of switching a 6A current? The current supply is from a car battery so the voltage will be 12V. I'm looking for the part number of the component...

PS: Where does one look to find appropriate components? I assume egineers don't post in forums when they want to find parts.. :D
 

SgtWookie

Joined Jul 17, 2007
22,210
If this were urgent, you would have at least put your general location (country and state or province) in your profile, as we have no idea where you are or what might be available there. I can only guess that you are not in the United States.

JFETs are not appropriate for controlling that much current. You will need a power MOSFET.

You have not described your load, or whether you wish to switch the high-side or low-side of the load; so we have no idea whether a P-ch or N-ch would be more appropriate.

You mention a car battery, but you don't mention whether this will be used on a test bench, as a lawn decoration, or if you are planning on using the circuit in a vehicle.
 

mcasale

Joined Jul 18, 2011
210
In general, you can find components by going to a manufacturer's web site. There you will find more information than is humanly digestible. Also, distributors (DigiKey, Mouser, Newark, etc.) have good search capabilities and can direct you to possible options.

I agree with SgtWookie that you need to be more specific about what you are trying to do before anyone can choose a part.
 

Thread Starter

mahela007

Joined Jul 25, 2008
45
If this were urgent, you would have at least put your general location (country and state or province) in your profile, as we have no idea where you are or what might be available there. I can only guess that you are not in the United States.

JFETs are not appropriate for controlling that much current. You will need a power MOSFET.

You have not described your load, or whether you wish to switch the high-side or low-side of the load; so we have no idea whether a P-ch or N-ch would be more appropriate.

You mention a car battery, but you don't mention whether this will be used on a test bench, as a lawn decoration, or if you are planning on using the circuit in a vehicle.
What do you mean by switching "high side" or "low side"?
 

wayneh

Joined Sep 9, 2010
16,399
You also haven't mentioned your switching frequency. The faster you need to switch that load, the more attention you must pay to the circuitry.

I'd use a IRF540 N-channel MOSFET placed between your load (drain) and ground (source). My choice is mostly because I have a few of them and I know they can handle that current without heat sinking, when driven properly (ie. at least 10V to the gate when on, zero volts when off. And, I've made some assumptions about the answers to the questions raised already.
 

SgtWookie

Joined Jul 17, 2007
22,210
What do you mean by switching "high side" or "low side"?
N-ch MOSFETs are used to control the ground (low side) of a load. They can also be used for high-side (positive supply side) switching, but the circuit is more complicated.

P-ch MOSFETs are frequently used to control the high side (positive supply) for a load. P-ch MOSFETs have more or less fallen out of favor, as all other parameters being equal, they require about 2.5 times more current than N-ch MOSFETs to charge and discharge the gate. As such, the selection for P-ch MOSFETs is much more limited than for N-ch MOSFETs.
 

Thread Starter

mahela007

Joined Jul 25, 2008
45
Why is it that N-channel mosfets must be connected so a specific side? Isn't the path for current identical in each case?
 

SgtWookie

Joined Jul 17, 2007
22,210
Why is it that N-channel mosfets must be connected so a specific side? Isn't the path for current identical in each case?
Because Vgs (voltage on the gate referenced to the source terminal) needs to be 5v (for a logic level MOSFET) or 10v (for a standard MOSFET) in order to be considered fully turned on.

If you have the drain of an N-ch MOSFET connected to your +V supply, how are you going to get the gate more positive than your +V supply? There are circuits to accomplish this; but it is not obvious how they work when you first look at them.

With a P-ch MOSFET, Vgs is -5v to turn on a logic-level or -10v to turn on a standard-level MOSFET.
 
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