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Old 5th March 2011, 08:26 PM   #1
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Default IRS27951 / IRS27952

Hi Guys!

I hope some of you heard about IRS27951 or IRS27952 from IRF. These are 8pin half-bridge resonant controller ICs, they have a lot of improvements from the common-known IR2153 series.
- progammable dead-time
- increased FET-driving current
- easier variable frequency controll
- over-current sense with FET's Rdson
Due to its highly-integrated, with very few external components a stabilized-output high efficiency SMPS could be built from few hundred watts, up to 1kW.
The problem is that they are really new, and I haven't seen them anywhere (farnell, digikey, tme).
Anybody seen this IC somewhere?
I would really get my hands on few peaces.
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Old 17th December 2012, 01:21 AM   #2
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I am currently in the process of making a half bridge SMPS using this chip.

I have got a pcb made and powered it up but it isn't working yet.
Its a pretty simple circuit so shouldn't take much fixing.
At the moment it looks like my aux supply isn't working.
I will let you know how I get on.
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Old 18th December 2012, 01:03 AM   #3
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I might have found the problem tonight, I put in a 200v diode where it needed to be at least 350 volts. This has probably killed the 27951.
I have removed the 27951 and am awaiting a new one.
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Old 18th December 2012, 07:56 AM   #4
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which diode was it? intersting thread, will you share with us?

btw , what is a good brand for the Cr , resonance tank cap. I found it hard to find caps that can take the beating @ 50-150 kHz...
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Old 18th December 2012, 11:09 AM   #5
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It is the Vb diode I got wrong.

I just used what ever I could get for the Cr capacitor, will see how it works out.
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Old 18th December 2012, 08:28 PM   #6
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The bootstrap diode? that needs to withstand the full voltage+bootstrap voltage + margin. In hte appnote they use a 600V diode.

You have to be careful with the capacitor, due to high voltage present at high frequency. The voltage rating derates rather quickly with frequency. There is a risk of overheating so be very careful, if it blows all that resonance energy will go somewhere and problably kill everything, or as moderator expressed it "annhilating primary silicon".
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Old 19th December 2012, 01:04 AM   #7
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I got some more 27951's in today.
Replaced the chip and it still doesn't work.

So I built up a pcb partially to run off 30 volts.
Even that doesnt work !!

I can only guess I have done something silly like fried the SMD when soldering it in.
I have soldered them in by hand.
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Old 19th December 2012, 01:11 PM   #8
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Bad luck, are you shure there is not anything else that it blown? frying a SMD chip is not impossible, but unlikely unless you really, really put the heat on (it).

It could have been ESD chocked though. Or fakes. Or DOA.

You have to work through it systematically .
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Old 22nd December 2012, 10:31 PM   #9
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Quote:
Originally Posted by rikkitikkitavi View Post
Bad luck, are you shure there is not anything else that it blown? frying a SMD chip is not impossible, but unlikely unless you really, really put the heat on (it).

It could have been ESD chocked though. Or fakes. Or DOA.

You have to work through it systematically .
I have ordered a soic 8 to dip converter. Will try that and if that doesn't work will try removing a 27951 from its packing without touching it and try that.
The circuit is so simple that I must be doing something very silly.
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Old 30th December 2012, 01:05 AM   #10
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I rigged up a 30 volt low voltage supply to my circuit so I can check it without killing myself on mains.

I found that the 27951 would only work at circa 14 volts VCC.
Above and below this voltage the signal just looked a mess.

I read through the datasheet again and this suggested using a star ground with the VB charge up ground separate from the RT and CT circuits and VCC.
I hacked my circuit to get as close to a star ground as possible and the circuit now works between 12 volts and 30 volts.
I then tried with a 90 volt supply and the circuit worked fine.
I tried again with mains voltage to the circuit but it seems to crash out and go into low power mode.
I am getting there slowly but have a little more work to do yet.
I will look at the auxiliary supply next to make sure the chip is getting enough power while working on mains.

Last edited by nigelwright7557; 30th December 2012 at 01:10 AM.
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