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ZakWolf

Tue Jun 19 2012, 09:11PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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Posts: 608

I do not have an oscilloscope and my electronic knowledge is limited when it comes to IC chips and Driving/powering a half bridge.

After crashing an burning with my previous PCB plasma speaker (circuit im using here)

I drew up a new one. I finished the board today and turned it on, i got a high pitch squeal coming from the board with no load and was able to adjust the frequency of the sound with the pot that was coming form the board.

Heat check, nothing was hot except the chip, so i attached a speaker to test the load and was able to adjust the freq.

Tested the output voltage and it was 1.5..Volts AC all the way to the milivolt range.

Im sure the GDT works because i tested it on a working board, plus i dont think thats where the problem is coming from.

After some more testing i over heated the chip and now when i replaced it wasn't oscillating or drawing any current.

I used all standard values listed in the schematic.

***Im not looking for a 100% answer more so where to begin looking for what would cause the chip to heat so much.***

tdlr Chip heating a lot, board making a high pitch squeal, now nothing works...

Thanks

brandon3055

Tue Jun 19 2012, 10:35PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Have you tested the regulator? The chip is probably heating because it has to run the gdt directly so unless your gdt is perfect sum heating can be expected to stop it you could try sum gate drive ic's

Alex M

Tue Jun 19 2012, 11:19PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Mine did that when I was using an unsuitable ferrite core, it drew lots of magnetising current that was more than the 100mA or so that the chip can supply without overheating. Try adding more primary turns on the GDT.

Also multimeter's are not accurate for high frequency AC. If its an auto ranging one then you might have to manually range it to see closer to the correct reading (I had this problem with low AC readings).

ZakWolf

Wed Jun 20 2012, 01:25AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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OK i will check it out, i think i might need more turns, and i will test the output on manual

*** So i removed some traces and added some wires to correct the GDT. But still no current draw from the ic, i switch out 3 and still nothing yet the voltage regulator still works.

What would inhibit from oscillating? ***

brandon3055

Wed Jun 20 2012, 06:45AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Try putting a cap on the output of the regulator I have had trouble with them playing up without a cap and if that doesn't fix it test the diodes and if they work test the mosfets and if it still won't work maby you have a dry solder joint somewhere or a broken track

ZakWolf

Wed Jun 20 2012, 07:03AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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copper traces -good

volt regulator-good

GDT-good

In the begging i powered up the bridge with neg and powered the ic side up, could i have burned out my mosfets in some sort of heat less silent manner?

How do i check the Mosfets ? with a multi metter

brandon3055

Wed Jun 20 2012, 02:19PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

What do you mean you powered up the bridge with neg if you mean you pos and neg the wrong way round that might have killed them (it is easy to.kill a mosfet without it getting hot maby the gate voltage was too high can you test them

Edit: another possible cause might be a faulty trimmer I have had that happen to me before

ZakWolf

Thu Jun 21 2012, 12:19AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Destroyer of mosfets wrote ...

What do you mean you powered up the bridge with neg if you mean you pos and neg the wrong way round that might have killed them (it is easy to.kill a mosfet without it getting hot maby the gate voltage was too high can you test them

Yeah i had reversed the input of the bridge, the trimmer works because i was able to change the frequency of the sound by turning it.

If the fets were dead would that account for the board not drawing any power?

thanks a million

brandon3055

Thu Jun 21 2012, 01:12AM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Only if you have a very good gdt (but it should still draw a few mA)

Edit: also it seems unlikely but maby one of your passive components are dead have you checked the 1uf on the gdt

ZakWolf

Thu Jun 21 2012, 03:26AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

No i havent checked the 1uf cap.

I replaced both Fets still nothing.

Could it be the .1uf caps the go to the ic or any of the Fast diodes ?

to check them i have to desolder them dont i ?

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