FET Transistor Substitution Question - Page 1
Forum section: electronics / beginners

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 13, 2016, 07:42:01 pm
content: Hey, I have two transistors here, one dead one and one good one from a "donor"I am curious, the specs vary wildly but which ones matter?2SK3797 - The Dead onePHP20NQ20T - The Potential Donor

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2016, 07:51:16 pm
content: Do you have a schematic? What's the device?The most important thing is probably the voltage rating. The original is rated to 600V but your proposed replacement is only rated to 200V.

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 13, 2016, 07:53:34 pm
content: The device is a 19v 9.5A DC computer power supply with an input of 120v.Its rated for up to 240v but will never be used in that situation.

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 13, 2016, 08:37:08 pm
content: Sorry to double post, but its so quick that I don't think it matters....I am searching mouser for replacements with about the same specs, but one spec I cannot get anywhere near what it's rated for:RDS (ON) = 0.32ohm is the original spec.all replacements I see are rated for .038ohm to .210ohmDo I need greater or less ? or does it even matter much?

author: Zero999
author_rank: Super Contributor
timestamp: February 13, 2016, 09:29:40 pm
content: You can probably use a lower voltage rating MOSFET if it's not going to be used at the full voltage but 200V might be too low. It's quite likely 600V was chosen for reliability's sake and because there will be spikes above the peak mains voltage. Going for 300V (half the voltage rating) will be safer.Generally the lower the on resistance, the better.

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 13, 2016, 09:41:26 pm
content: Quote from: Hero999 on February 13, 2016, 09:29:40 pmSo it looks like all of the drop-in replacements will be a better fit because they are all lower resistance. I was thinking the same thing on the 120 vs 240, half is probably acceptable.I'm assuming that then, the NTE2394 will be an acceptable replacement then.LOL but for my local FRY's price of $9.99 each I think I'll wait to buy 3 from mouser for $4.50 each.

author: Zero999
author_rank: Super Contributor
timestamp: February 16, 2016, 08:18:27 pm
content: It's electrically compatible but not mechanically: the NTE2394 is physically larger than the 2SK3797.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2016, 01:39:04 am
content: Lower Rds(on) is most likely fine. Qg(tot) should be similar, otherwise EMI response will be very different.http://www.digikey.com/short/3t1tcm(if the link works..?) the first 20 are under $3 in small quantity, so go nuts.Tim

author: DivineChaos
author_rank: Regular Contributor
timestamp: February 27, 2016, 07:30:52 pm
content: The link worked, thanks. Yeah, I ordered those NTE before I read the post and I was shocked to see that they were quite large in comparison.For some reason Digikey will not let me make an account. I need to be a "business" or something of the likes. I remember it was a pain and Mouser is what I stuck with because I created an account immediately and it was easy to get my first order out.