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JojoD818 8th August 2006 07:15 AM

Matching MOSFETS
 
Hi,

I need to match Vgs for a bunch of IRFP240 and IRFP9240 transistors. Did I get the test circuit correct for the N-channel and P-channel? Just flippin' the connection for the drain and source right?

What test current can you suggest for this power packs? The 220 ohms is for a current of 50mA.

Thanks!

http://www.filehigh.com/serve/13381/209464.jpg

JacekPlacek 8th August 2006 12:58 PM

I do not know what is topology of Your project but if You want only Ugs be the same ( for different currents ) You should force exact the same currents for both transistors as will be in Your application. Characteristics of transistors are nonlinear ( here You have additionally strong different transistors )so You shouldn't take arbitrary 50mA. Set the same currents as in circuit.

Regards
Jacek

jackinnj 8th August 2006 02:35 PM

I use a constant current source power supply -- a Tektronix PS5010 which will drive an amp through the devices -- while the CCS gets you an ampere to 3 significant places you have to maintain a constant ambient temperature AND a constant period of time in which to measure VGS.

I don't think you need a lot of digits behind the decimal point to get reasonably well matched devices -- and there are a number of other parameters to match for if you are so inclined -- but generally a tube of 25 or 30 devices will have pretty consistent Vgs (by that I mean, a normally distributed group) with a couple of outliers, and the outliers can always be used in power supplies.

JojoD818 8th August 2006 03:51 PM

Guys,

Thanks for the replies. I will be using the trannys for an F1 clone. I drew the pic of the test jig from Mr. Pass's way of matching mosfets. Unfortunately my eyes are a bit confused as to the orientation of the fets.

This is the link: http://passdiy.com/howto/matching.htm

Thanks!


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