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andrewlebon 11th November 2012 11:24 PM

smps
 
Hello
greetings i picked up a smps of a audio amplifier from junk disposal
both IGBTs are short can IRF460 be used to get it working and when working
i can change to igbts as these igbts are pretty expensive
warm regards
andrewlebon:confused:

nigelwright7557 11th November 2012 11:31 PM

I usually pop in a new mosfet then power it up with light bulb in series with mains.

You could also check before power up for shorted electrolytics.

Sch3mat1c 12th November 2012 03:10 AM

I'd say probably not. IGBTs are generally easier to drive than MOSFETs, especially in the same size. Putting in a MOSFET, especially such a horrendously ancient one, let alone one probably oversized, will probably drag it down and make more smoke, even on a light load.

It depends on design of course, but if it's generic consumer crap, it's going to be marginal at best as-is. And apparently not good enough, seeing as the transistors did fail!

Tim

DUG 12th November 2012 04:36 AM

1 Attachment(s)
Sch3mat1c, IGBT is like an MOSFET and BJT combined...some are like MOSFET and SCR combined and they actually latch like an SCR.

They drive like a FET but have benefits of BJT.

andrewlebon, review the datasheet for the IGBT and see if the IRF460 can be used in place of the IGBT.

Find which parameters are different and if those parameters are important or relevant in the smps you are working with.

have fun learning

andrewlebon 16th November 2012 01:34 PM

SMPS HELP
 
2 Attachment(s)
Hello
greetings pics of smps 700 watt using igbt 100 watt bulb glowing indicating SHORT have changed all trs and ic but still showing short any
logical way to rectify fault any help is WELCOME PLEASE
warm regards
andrew lebon:confused:

andrewlebon 16th November 2012 01:37 PM

board on the right with TOP44-YN is giving 16 volts dc so its working other ic SG3525A
and LM339 also changed same result bulb glows
warm regards
andrew lebon

Sch3mat1c 17th November 2012 12:43 AM

Quote:

Originally Posted by DUG (Post 3238207)
Sch3mat1c, IGBT is like an MOSFET and BJT combined...some are like MOSFET and SCR combined and they actually latch like an SCR.

Hmm, the attached symbol is neither accurate nor representative of actual devices. The most common model is a PNP transistor, with its emitter as "collector" output, base to NMOS drain, and the PNP collector, NMOS source and substrate to "emitter".

The most common schematic symbols are either an NPN transistor with an insulated gate (poorly suggestive of actual nature, but representative of use), or a more detailed symbol with the segmented substrate of an enhancement mode FET, with diagonal lines and arrows suggesting the minority carrier structures.

The advantage of an IGBT is lower voltage drop and gate charge than MOSFETs; the disadvantage is low speed (due to minority carrier recombination) and lack of a resistive range (so that MOSFETs are preferred when Vds/Vce ratings are under about 300V). Thus, replacing an IGBT with a MOSFET, amp for amp and volt for volt, will increase gate charge and impair switching rate (the IGBT's slower nature is already accommodated by circuit design and doesn't count twice).

An old MOSFET, like IRFP460, has easily twice the gate charge, and higher Rds(on), than comparable newer MOSFETs. Comparable newer IGBTs have 60% lower gate charge than those MOSFETs, or less than 80% of an IRFP460. No guarantee, of course, that they chose an IGBT of the correct size, but one can always hope.

Tim

sawreyrw 17th November 2012 03:53 AM

Andrew Labon, please learn to use capital letters and puncutate.

sawreyrw 17th November 2012 03:54 AM

It is highly unlikely you can use a MOSFET as a direct replacement for a power MOSFET.

DUG 17th November 2012 04:38 AM

3 Attachment(s)
Sch3mat1c, you are correct about the jpg I posted, I don't know what part of my memory that pix came from.

Here are some better ones from that internets thing.

The first one is the PNP/NMOS you mentioned.

The second and third ones are the latching types

The third model with the J-FET is from IXYS Corp. I've never seen that one before.


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