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LAN_403

SilentCoronas

Thu Aug 06 2009, 10:34AM

Registered Member #2171 Joined: Thu Jun 11 2009, 10:15AM
Location: Denmark, 8700 Horsens
Posts: 4

I made this PCB from UZZORS2K' Schematics, but it seems to be runnig very hot on the four transistors. The PCB version is drawing as much as 1A.. breadbord only 0.09 at all times? This is my 2nd layout attempt. Would anyone be so kind as to check it out for me, as i am unable to see what i did wrong here.. heres a flick of PWM running off breadboard and hardwired powerstage : http://www.youtube.com/watch?v=E-dpI6KSGBQ

Hope you'll help me out

Mads Barnkob

Thu Aug 06 2009, 02:05PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I did not find any errors in your PCB, are you using the same GDT as you used on the breadboard?

SilentCoronas

Thu Aug 06 2009, 02:45PM

Registered Member #2171 Joined: Thu Jun 11 2009, 10:15AM
Location: Denmark, 8700 Horsens
Posts: 4

MadsKaizer wrote ...

I did not find any errors in your PCB, are you using the same GDT as you used on the breadboard?

Hi Mads, thx for posting!

Yes I used the same GDT. Made a powerstage PCB too, seems the breadboard PWM runs high driving that, so I thought it was that at first, but my PCB'ed PWM runs hot on the Hardwired powerstage aswell, not as badly though, also seems to draw more current at lower frequencies. I have interchanged all my available setups, and I think my Halfbridge PCB has a problem since both breadboard PWM and PCB'ed one runs hot on it, just cant seem to figure out where i messed up! Here is the halfbridge:

uzzors2k

Thu Aug 06 2009, 06:00PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

I can't see anything wrong with the half-bridge PCB either. Maybe use larger spacing between the traces, as there is significant differences in potential between them. Have you tried a quick lash-up bridge to see if it causes heating too?

SilentCoronas

Thu Aug 06 2009, 06:32PM

Registered Member #2171 Joined: Thu Jun 11 2009, 10:15AM
Location: Denmark, 8700 Horsens
Posts: 4

Hi uzzors!

yup, tried feeding my lashed up bridge, the one i used in the tube-vid, lower heating, but draws around 220mA (breadboard 90-110mA) full duty cycle, also when I lower the frequency, it's still pulling 1A or so.. Will space out the paths some, knew it was probably a bit tight with just .5 mm. Set up my breadboard driver with my pcb bridge, and it instantly pulled over 1A. Checked all components are in their right places, and caps polarized right too.. Parts are from farnell, checked values and they are all good. Apart from heating up, the PCB's perform fairly, as long as i avoid running at lower frequencies. Being the noob, I hope I make sense:-p

uzzors2k

Fri Aug 07 2009, 04:07PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Do the transistors heat with no GDT present? The frequency dependency sounds like a GDT problem, ie saturation. I just noticed you've used a very old schematic, I've since started using some "fixes":

1) DC blocking capacitor.
2) A single damping resistor on the primary side of the GDT, and none on the secondary.

See my newer schematics if you don't know where to put these. The DC blocking capacitor will prevent saturation by any unevenness in the waveform, while the primary damping resistor won't explode if the bridge does, and is 1/2 the price of using two.

SilentCoronas

Fri Aug 07 2009, 05:45PM

Registered Member #2171 Joined: Thu Jun 11 2009, 10:15AM
Location: Denmark, 8700 Horsens
Posts: 4

Thx for the advice, I'll try it out and see what happens.

The transistors doesn't heat much either with or without the GDT, so I think now my problem is in the bridge. when i drive the lashed-up bridge from the PCB driver, only moderate heating occurs. My breadboarded driver hates the bridge PCB. I am tempted to dump this project, and move onto your newer stuff, but I'd sure like to know what went wrong, and learn from it.

Now armed with newer schematics, and some fresh parts in the mail, i am set for a weekend of experimenting and reading.. what is puzzling me, is that the breadboard and lashed-up setup is working great, and the PCB's should be ok, and with excact same components in them, yet they act up. also did scope out my GDT's and the new commercial pulse transformers i got, and they seem to tolerate the frequencies quite well, pretty nice square waves, and my own toroid being the better of the two. did xperiment a while and ended up with 30 trifilar windings on a EPCOS - B64290L618X38 - FERRITE RING CORE, 25.3X14.8X10 http://www.farnell.com/datasheets/80884.pdf - Anyhow i will see if i can get your newer setup put together, and see where that takes me. need to gulp down a fair bit of theory aswell!

ordered some MCP1407-E/P driver IC's, to try and get rid of them lil 139/140's aswell... think they should do ok?

Cheers, Sean

uzzors2k

Fri Aug 07 2009, 06:12PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

30 turns on that type of core should handle relatively low frequencies. I always use B64290L618X'830' cores for my GDTs which have lower Âµi, so yours will preform even better. Replacing the BD1XX'es with gate driver chips is a good idea.

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