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Old 17th January 2013, 02:07 AM   #141
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Quote:
Originally Posted by lorylaci View Post
There is some error with Fmin.
I get 56kHz. The 28kHz is unreal.
I ran my signal generator into the LC network and I get a huge peak roughly around 23KHz. I tried to find the upper resonant frequency but if it is there it is small compared to the lower resonant frequency.

I designed a USB LC meter a couple of years back and I built one up to check my readings compared to my LC hand meter. The USB meter says it is 625uH and 10uH. I don't believe its 10uH I believe the 125uH open circuit reading on my handheld meter. Even if it was only 10uH it isn't the main resonant frequency used by the system.

So it looks like the resonant circuit is ok.

I tried 1000pf as the dead-time capacitor and there was no joy there, I obviously altered the Rmin and Rmax to suit.
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Old 17th January 2013, 09:09 AM   #142
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Quote:
Originally Posted by nigelwright7557 View Post
If I use 1k as Rmin the 27951 powers up every time.
This gives a frequency of 500,000Hz

Something is seriously wrong as it should run easily at frequencies below this.
The softstart should dictate that high frequency when starting up.
Your Rmin values is bad, as i pointed out previously (Fmin is not the lower resonant frequency), I get different values fromt he spreasheet also.
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Old 17th January 2013, 09:13 AM   #143
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Quote:
Originally Posted by nigelwright7557 View Post
I ran my signal generator into the LC network and I get a huge peak roughly around 23KHz. I tried to find the upper resonant frequency but if it is there it is small compared to the lower resonant frequency.

I designed a USB LC meter a couple of years back and I built one up to check my readings compared to my LC hand meter. The USB meter says it is 625uH and 10uH. I don't believe its 10uH I believe the 125uH open circuit reading on my handheld meter. Even if it was only 10uH it isn't the main resonant frequency used by the system.

So it looks like the resonant circuit is ok.

I tried 1000pf as the dead-time capacitor and there was no joy there, I obviously altered the Rmin and Rmax to suit.
No, no, no Nigel. You are messing things up again.

With no load, on a bode plot you will see the lower resonant frequency.
Now: short the outputs of the transofrmer. Then you will see the upper (MAIN) resonant frequency on the bode plot. Try this experiment!
Also it will check your LC meter.

Do your transformer wound on split bobbin? (Or do your priamry and secondary wound on the oppsite side of the bobbin?).

Dead time is (normally) not related to the max current. Dead-time should be set to get ZVS with your FETs Coss. If you do not understand what ZVS means, do not worry. I can tell you.
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Old 17th January 2013, 03:28 PM   #144
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For some reason my pcb has stopped working, there is no HO and LO outputs.

So I tried another pcb and cant get any 27952's to run. I tried 3 and none worked.
Something is seriously going wrong with my soldering. I am using a heat gun but I think it is blowing up the 27952's.

I think I have spent too much time chasing something that is not going to work for me.

I am going to see if I can find a through hole IC that I can work with instead.
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Old 17th January 2013, 04:47 PM   #145
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SOIC8 not thermally enhanced aren't hard to solder and I'd be surprised if you were cooking them, unless you were continuing to apply heat for a long time after the solder had started to melt. If your eyes are bad just use a nice magnifier. I've got good eyes but msop parts are hard for anyone to see. I solder them somewhat blind and then use a magnifier with solder wick/fine tip/solder and the continuity sensor to check things are soldered properly.

The easiest method to solder a soic8 part would be to try soldering each pin manually with an iron and not caring if you solder two legs together. Then use solder wick to remove any excess solder.

The magnifier is essential in allowing me to see what needs to be seen with those smaller parts.
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Old 17th January 2013, 09:12 PM   #146
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I will order some more 279052 and solder them in quickly by hand.

The heat gun was set to 300 degrees and I had to hold it on for about 90 seconds.
Its hard to see when the solder melts as I put very little on the pads to stop it going over two pads.
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Old 17th January 2013, 09:38 PM   #147
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Quote:
Originally Posted by nigelwright7557 View Post
I will order some more 279052 and solder them in quickly by hand.

The heat gun was set to 300 degrees and I had to hold it on for about 90 seconds.
Its hard to see when the solder melts as I put very little on the pads to stop it going over two pads.
Nigel, search youtube for soldering video tips. 90 seconds is "90 seconds of death" for the ICs.

I use simple temperature controlled soldering iron, and I usually use excess solder. If it is too much, I just use a coopper strand (image below) to remove excess.
Click the image to open in full size.
It is pretty easy.

It is so sorry to hear you give up. If you are interested, I can send you a presoldered controller board by post (pictured a few post earlier)

From the Hungarian forum so far two guys built LLC converters after my article. One of them was quite successful, now he is on a Class-D project. None of them complained about SMD soldering.

As you could figure out, LLC converter is my favourite magical thing. From my first design (weel, actually the third prototype of that design), tahat is on that article I was able to pump out 400W cont and 500W peak from 12x8x4 cm.
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Old 17th January 2013, 10:02 PM   #148
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Originally Posted by lorylaci View Post

From the Hungarian forum so far two guys built LLC converters after my article. One of them was quite successful, now he is on a Class-D project. None of them complained about SMD soldering.
.
I have already done the class d thing. It took a couple of revisions of circuit and pcb to get there but I have a design that does 250 watts to 750 watts.
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Old 18th January 2013, 02:54 AM   #149
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I had a look on you-tube at SMD soldering techniques.
90 seconds is too long so I have most likely fried the 27952's.

The last one that worked was hand soldered in. I soldered it in as quickly as I could.
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Old 22nd January 2013, 10:08 PM   #150
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I bought some more 27952's.

I soldered in the first and checked my circuit for shorts between pins.
It had a short between pins 7 + 8 so I took the chip back out and there was no short on the pcb but pins 7/8 were shorted on the 27952.
So I soldered another one in and this one powers up on low volts, with a nice square wave on the output.

I tried to power it up off mains but I just get a brief pulse on the output then it stops and discharges.

Any suggestions where to go to next ?

I currently have:
Resonant frequency = 95k
Max switching frequency = 190k
soft start frequency = 400k

Rmin = 10k
Rmax = 2k2
Cr = 1000pf


Running off 30 volts the switching frequency is 55k
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Last edited by nigelwright7557; 22nd January 2013 at 10:25 PM.
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