IC identification needed for 2500w "Mobile Power" Inverter

[cornwallav8r]

I am trying to repair a 2500 watt inverter, but the danged Chinese manufacturer etched out the ID of the particular IC I know to be bad, it is a driver for the high voltage output PMOS transistors. I replaced all the transistors, but one of the little driver diodes shorted and took out the chip, I can see a burn mark on it. The unit powers up and gives a green status led bud doesn't make 120vac so I know this is at least one ofthe remaining problems, if not the only one.

Somebody else must have gone through this already right? What are the typical ICs used in these inverters? I know typically they use simple ICs like op amps and counters. The chip in question is Q3, it's an 8-pic IC with driver outputs on pins 11 and 14....

 

[Resqueline]

There sure wasn't much useful information here to use in trying to help you out..
An 8-pin IC with its outputs at pins 11 & 14...? Come on, you can do better!

 

[cornwallav8r]

There sure wasn't much useful information here to use in trying to help you out..
An 8-pin IC with its outputs at pins 11 & 14...? Come on, you can do better!

Well I wasn't trying to completely describe the circuit but rather describe the situation, hoping others had similar situation or access to similar product to determine the chip ID.
But I guess you may be right, I may need to draw the whole surrounding circuit to get further along.

 

[(*steve*)]

I was thinking how special this 8 pin device was to have its outputs on pins 11 and 14! Do the pins start from 9 in this device?

 

[cornwallav8r]

I was thinking how special this 8 pin device was to have its outputs on pins 11 and 14! Do the pins start from 9 in this device?

Well had I known you guys would be smart-alecs I would've supplied more chip info in the first place!
But seriously, I was concentrating on the area of damage, and there are 2 banks of large PMOS's fed by pins 11 and 14, but may be feeding other banks from other pins, I will investigate further when I get a chance. Thanks a bunch for showing interest. I love a good mystery. I suspect this is just an op amp or something else generic as are the other chips I can read, but we will see.

 

[cornwallav8r]

Well had I known you guys would be smart-alecs I would've supplied more chip info in the first place!
But seriously, I was concentrating on the area of damage, and there are 2 banks of large PMOS's fed by pins 11 and 14, but may be feeding other banks from other pins, I will investigate further when I get a chance. Thanks a bunch for showing interest. I love a good mystery. I suspect this is just an op amp or something else generic as are the other chips I can read, but we will see.

Oh and excuse the typo it is 16-pin!!

 

[(*steve*)]

I actually missed your typo the first time I read it.

I re-read it and considered that the chip might just be a dual mosfet driver or something (as they come in 8 pin packages). I was going to look at the common ones and see if any of those had the outputs on pins 11 and 14.

*Then* I noticed it

Unfortunately it also means that it would be fruitless to look at mosfet drivers...

 

[cornwallav8r]

I actually missed your typo the first time I read it.

I re-read it and considered that the chip might just be a dual mosfet driver or something (as they come in 8 pin packages). I was going to look at the common ones and see if any of those had the outputs on pins 11 and 14.

*Then* I noticed it

Unfortunately it also means that it would be fruitless to look at mosfet drivers...

Here is a pic of the IC in question...in middle of the pic, U3. Note the diode with blue brackets adjacent, D13, which was blown open. It is driven off pin 11, and the diode D12 with similar function is driven off pin 14, and there are likely more, just haven't investigated that far.
Thanks for showing this some attention.

 

[cornwallav8r]

A bit more clarification...this IC's purpose is definitely the PMOS output driver. Its outputs are pins 11 and 14. Each pin feeds 3 parallel IRFP250 high voltage PMOS transistors through a high speed diode (one diode per gate). That makes up half what I assume to be an h-bridge. The same pins 11 and 14 feed bases of (inverter) transistors (ex: Q19 in the pic). the transistor collectors connect through a low ohm resistor (ex: R50) to the gates of the other half sets of PMOS outputs. I will provide further clarification as I can. Thanks

Overall pic attached.

 

[Resqueline]

Now at last we're getting somewhere..
There are some high-side low-side drivers with that kind of pin numbers. I'll have look tomorrow if some chips I have come across might fit.

 

[cornwallav8r]

Now at last we're getting somewhere..
There are some high-side low-side drivers with that kind of pin numbers. I'll have look tomorrow if some chips I have come across might fit.

Attached please find a little autocad dirty sketch I made to try and nail this down.
Hope this helps. Also note there are 2 other similar sized unknown ICs with VCC +12v at the same pins 13 and 15. I find that reassuring, in that these are likely common purpose ICs, since they do not appear to be doing the same thing as this burnt one.

 

[55pilot]

If the MOSFETs are IRF, the drivers may be from IR as well. I would go and look at the IR website for MOSFET drivers or bridge drivers. IR sold a bunch of their portfolio, but I think they retained the drivers.

Good luck.

---55p

 

[(*steve*)]

IRFP250 high voltage PMOS transistors

That would be NMOS, since those transistors are N Channel Mosfets.

The photos are really of assistance. It looks like there's 2 of these chips on the board, lending weight to the fact that they're drivers, not SMPS controllers.

 

[cornwallav8r]

NMOS, thanks for correcting me. I hope the diagram helps. I reviewed all the 16 pin IR drivers, and none of them matches the pinout requirement. I highly suspect that the parts are not dedicated drivers but something more generic and cheaper to supply.

 

[cornwallav8r]

REVISED DRAWING ATTACHED

 

[cornwallav8r]

NMOS, thanks for correcting me. I hope the diagram helps. I reviewed all the 16 pin IR drivers, and none of them matches the pinout requirement. I highly suspect that the parts are not dedicated drivers but something more generic and cheaper to supply.

Lookie what I found! I took apart a much smaller inverter, the chips were all predictable, i.e. CD4013, LM324, an NE556, then I saw this single SG3525, did a search and found this circuit...see attached. it appears at first glance to have the same pinouts....but used as a speed controller?

 

[(*steve*)]

Good find. But check out the datasheet. There are 2 different versions. They have outputs that are logically inverted. I don't think you'd want to put the wrong one into the circuit.

On second thoughts it may not matter, since there appear to be a set of mosfets driven by the logically inverted output signal.

Is it just me, or does anyone else think that the three mosfets turned on (presumably) by the transistors need something to turn them off again.

 

[55pilot]

It really does make a difference. You need to use the version with the "On = High" output stage. The data sheet is a little confusing, but it is the "SG1525A" drawing on page 2 of the datasheet. If you use the other one, you will blow the MOSFETs because they will be on at the same time.

The circuit drawn by cornwallav8r is s little suspicious, but it could be just poor drawing. I can see pins 11 and 14 driving 3 MOSFETs each with the resistor/diode combination. The driver is terribly under-powered, but it will work.

I do not understand what the transistor is doing, but it could just be poorly drawn. The only thing I can think of is that the transistor is pulling the other set of MOSFETs' gate low. So when pin 11 is high, it drives its MOSFETs on, while the transistor pulls the gates of pin 14's MOSFETs low. This will supplement pin 14's output drive to keep those MOSFETs off even as their drains are whipped high by pin 11's MOSFETs turning on. We need a better drawing to know for sure what the circuit is doing, but that woudl be my guess.

Much more importantly, if the driver is dead, it may be because something else in the circuit killed it. Just replacing it is not going to help until its killer is identified and fixed.

---55p

 

[55pilot]

Just to add, the transformer likely has a center tapped primary. The center is connected to 12V. The two MOSFETs alternately connect each end to ground. That results in AC voltage in the secondary, which is the 110V AC output.

---55p

 

[cornwallav8r]

Well here is good news, I just received an unexpected response from the seller of this unit...I asked him to look inside a defective one and here is what he responded with:

U3 - Fairchild 3525
So unless there are different versions of the 3525, my guess is right.

55pilot, the transistor appears to be an inverter voltage follower, inverting the signal to supply the other half of the h-bridge. And the driver is dead because one of those little driver diodes shorted when a bunch of the NMOS outputs failed. The diode was found blown open and replaced.