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Bauerb2

Mon Oct 01 2007, 09:52PM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

while working on my own sstc i felt the gate drivers to get rather hot. i fixed this by adding two electrolyte 22uF caps in series, negatives terminals soldered together, with all this in parralell with a 100nF ceramic cap. this is in series with the tc4429 output. i see on the schem you have that there is one 4.7uF in series. it might be worth a try to try my idea (taken from this site

)

its worth a try, it made my rise/fall times much quicker. (@ 380kHz sec)

-pz --Andrew

Dago

Mon Oct 01 2007, 10:48PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

huben Panev wrote ...

So hire are the traces. They are the gate - source signals. The top one is with 2 ICs (like on the schematic) and the bottom one is with 4 ICs (2 in paralel). The scope is set to 0.5 micro seconds/div and 10V/div. So what do you think about them ???

What kind of decoupling do you have for the gate drive chips? It is absolutely essential to have atleast something like a 100nF ceramic and a 10-40ÂµF tantalum OR low esr electrolytic cap as near as possible to the Vcc and GND pins of the gatedrive chips to achieve fast risetimes. The chips do get hot, mine get too hot to touch comfortably without some airflow at 50% duty cycle.

CT2

Tue Oct 02 2007, 01:57AM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

Yeah as stated previously your gate drive chips will get hot. You need caps on the supply pins (as close as possible). I use a 15uF tantalum and a bigger electrolytic as close as I can get them to the chips and then a 1uF ceramic practically on the pins, even still they run hot. So I had these little heat sinks that fit perfectly on the chip so I just slopped some thermal grease on the chip and stuck the heat sink on. With even a little air flow they run warm but not too hot.

The tantalum is hidden under the heat sink.

About the phase/frequency relationship... well I don't even own a scope so I've never looked at what my PLL is doing, so can't help there.

Dr. H.

Tue Oct 02 2007, 05:43AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Thanks for the replys guys.

I've copied the circuit with no changes, so for decoupling on the drive chips i have only one 4.7uF and it is electrolitic

. Today i will add some tantalum and ceramic condensers. For the decouplink i use 3uF (on the picture of the board the 3 yellow caps put side by side. Are this good ?

Bauerb2 - thenks for the idea. I will trye this too. Is there any chance that the waveform looks like this due to the ferite core (it is NOT the yellow one from ATX. Also could this be due to too much windings on the GTD (15 primary and 2x15 secondary )

CT2 - very nice design, i too may trie something like that

Marko

Tue Oct 02 2007, 10:01AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

On the core you are using you won't need to use more than few turns for 450kHz. See this

Your drivers are also inherently a bit slow. I would use UCC's whenever I could.

Dr. H.

Tue Oct 02 2007, 10:12AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi Marko, yes the ICs are slower than the UCCs but i can't find to buy them hire in Bulgaria, so i have no choice

Also in the schematic it is shown to use 16 !!! turns. I also thought that they are too much but after all i winded 15. Hire are the new scope pictures after some changes that the other guys suggested. If you think that i need to change the number of turns i will make it

The top picture is with 2 ICs and the bottom is with 4 (two in paralel ). Shoud i use 4 or could stick to 2 ???

Bauerb2

Tue Oct 02 2007, 11:08AM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

as far as fall/rise times go in both of those waveforms, i think you'll be fine with two. the rise times are a 'little' sluggish by my view of the 2 IC waveform, but if you could, when you start up your coil at low power, try first with 2 then with 4 to see which one performs better. that's what i'd do.

Dr. H.

Tue Oct 02 2007, 11:26AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Should i try reducing the number of windings on the gtd ? How this will change the waveform ?

Bauerb2

Tue Oct 02 2007, 07:59PM

Registered Member #973 Joined: Tue Aug 28 2007, 07:32PM
Location: Pittsburgh, PA
Posts: 66

as you add more turns to the gdt, the waveform starts to look more like a sine wave rather than a square wave. less turns, as i just tested right now (6 turns) , shows the waveform has lost structure and looks like small 6V rounded pulses on the scope. the driver IC's heated up incredibly (burnt my finger) in seconds. this was tested with 2 tc4420's with halfbridge irfp460's and then tested again with a full bridge of 460's. each mosfet has a 10 ohm gate resistor.

it seems i am having some insane trouble with my gdt, i can never get a clean signal. it could be the fact im trying to drive a full bridge with one gdt with one primary, and only 2 driver ic (6 amp each). hehe perhaps, but i dont have 2 similar toroid inductors to use... oh well

wish you luck

-andrew

Dr. H.

Tue Oct 02 2007, 10:04PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi Bauerb2 i actually tried reducing the winding on the gdt. I am now using only 7 turns (compared to the initial 15) and the waveform become litle bit better and the driver chips are running cooler, much cooler than before. I also reduced the gtd decoupling capacitor to 470nF and that improved the waveform further (strangely, any one for explanation ??? ) Tommorow morning i will post the scope traces )

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