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ZakWolf

Tue Feb 05 2013, 06:15AM

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

Schematic

and site

So about 8 months back I had poured my heart and soul in to a new PCB plasma speaker design and build. Only to find out it didn't work, after a month of debugging i quit building and designing things for about 8 months; here i am starting up again and decide to give it another go, It turns out i over looked a fried voltage regulator :O!!! so everything works now but the sg3525 is getting really hot.

Question: If i "tune" GDT (adding more or less turns) will it make the ic run cooler?

Alex M

Tue Feb 05 2013, 08:42AM

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

Sounds like the gate drive transformer core is not suitable and its drawing too much magnetising current from the IC.

Adding more turns will increase the inductance and lower the magnetising current, but this also increases leakage inductance (bad thing).

Fair-Rite 5977006401 Type 77 Material works well for these.

Personally I would recommend using some gate driver IC's between the SG3525 and gate drive transformer too, I got much better waveforms that way. But since you have already designed a PCB I guess there isn't much you can do about that. Do you have a scope?

ZakWolf

Tue Feb 05 2013, 03:54PM

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

Alex1M6 wrote ...

Sounds like the gate drive transformer core is not suitable and its drawing too much magnetising current from the IC.

Adding more turns will increase the inductance and lower the magnetising current, but this also increases leakage inductance (bad thing).

Fair-Rite 5977006401 Type 77 Material works well for these.

Personally I would recommend using some gate driver IC's between the SG3525 and gate drive transformer too, I got much better waveforms that way. But since you have already designed a PCB I guess there isn't much you can do about that. Do you have a scope?

hey thanks, no i dont have a scope :(

I have some other cores laying around i only have 11 turns on this one so i will rewind it and see if that helps

Alex M

Tue Feb 05 2013, 04:03PM

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

I have an idea, try it with something like 16 turns and check for heat. If the chip stays relatively cool then remove a turn and repeat. I have 14 turns on my gate drive transformer for this circuit, but that is with a "good core".

Also, this isn't really related to the above but put a 100nF film capacitor across the power and ground pins of the IC directly under the chip. Plus an MKP capacitor of around 470nF at the top FET's drain pin and bottom FET's source pin.

The first capacitor really helps cut down switching noise from the IC and the second one helps keep the arc free of noise caused by wire inductance.

ZakWolf

Tue Feb 05 2013, 06:17PM

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

Alex1M6 wrote ...

I have an idea, try it with something like 16 turns and check for heat. If the chip stays relatively cool then remove a turn and repeat. I have 14 turns on my gate drive transformer for this circuit, but that is with a "good core".

Also, this isn't really related to the above but put a 100nF film capacitor across the power and ground pins of the IC directly under the chip. Plus an MKP capacitor of around 470nF at the top FET's drain pin and bottom FET's source pin.

The first capacitor really helps cut down switching noise from the IC and the second one helps keep the arc free of noise caused by wire inductance.

Awesome, thanks for the help. I will post a video some time down the road

ZakWolf

Tue Feb 05 2013, 06:28PM

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

sorry for the double post i cant edit+upload a pic

Is that where the 100nf cap(blue) and the MKP cap (red) is supposed to go...?

Could you change it if its wrong...

Thanks in advance

Edit forgot to add the pic :( i dont want to tripple post i will add it to attachments

Alex M

Tue Feb 05 2013, 06:54PM

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

That is exactly where they go. Just make sure they really are soldered directly at the pins and not several cm away, or else their effectiveness will be cancelled out. In other words they are decoupling capacitors.

Also the shape of the electrode really helps make a silent arc. Vertical with a pointed bottom electrode and larger top electrode works well. For the top electrode I used a keyring with good results.

Have fun, I have destroyed quite a few LOPT's with this sort of driver

ZakWolf

Tue Feb 05 2013, 07:08PM

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

Alex1M6 wrote ...

That is exactly where they go. Just make sure they really are soldered directly at the pins and not several cm away, or else their effectiveness will be cancelled out. In other words they are decoupling capacitors.

Also the shape of the electrode really helps make a silent arc. Vertical with a pointed bottom electrode and larger top electrode works well. For the top electrode I used a keyring with good results.

Have fun, I have destroyed quite a few LOPT's with this sort of driver

Sweet, thanks for the help i love this driver.

and i will try out the spark gap you mentioned :D

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