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ZVS Charger Transformer

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LAN_403

currentkills91

Fri Jun 15 2012, 10:23PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I am, once again, making another charger, and I have an ungapped ETD34 core I'm using for the transformer. I was wondering if i should leave it ungapped or sand the middle legs down a bit to make a gap. I have read a few threads and I have gotten 2 different answers to this question. Some of them say to have a gap, and others say no gap is the best. I want to make the most efficient transformer I can, Because hopefully this will be my last attempt at this.

Steve Conner

Sat Jun 16 2012, 08:04AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

ZVS won't work without an air gap. Ferrite is very hard and difficult to grind down, so I just stick a piece of card between the core halves.

currentkills91

Sat Jun 16 2012, 06:18PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

Well I decided to test it anyway last night, and just used tape to hold the cores together tightly. It worked well except for the horrible oscillating noise, it was really more of a squeal. Will it still work the way it should if all three legs have a gap?

Steve Conner

Sun Jun 17 2012, 08:29AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes. At least it's worked every time I've tried it.

Dr. Dark Current

Sun Jun 17 2012, 09:42AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Remember if you build the transformer in a low-leakage way (coils on top of each other), you will need some kind of current limiting, eg. an inductor or a capacitor on the output.

m4ge123

Sun Jun 17 2012, 10:48AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

Why doesn't ZVS work without an air gap? I always thought it did.

Inducktion

Sun Jun 17 2012, 05:29PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Yeah.... I thought with a ZVS driver you want to minimize the air gap to reduce leakage current.

It's not a flyback mode driver, so what purpose would the air gap even do?

plazmatron

Sun Jun 17 2012, 06:13PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

I always thought the air gap was there to prevent core saturation.

Edit: Just found this:

"The only difference is the value of the
magnetizing inductor. While the series resonant converter
has a magnetizing inductance much larger than the LC
series resonant inductor (Lr), the magnetizing inductance
in LLC resonant converter is just 3~8 times Lr, which is
usually implemented by introducing an air gap in the
transformer.

An LLC resonant converter has many advantages over a
series resonant converter; it can regulate the output over
wide line and load variations with a relatively small
variation of switching frequency. It can achieve zero
voltage switching (ZVS) over the entire operating range.
All essential parasitic elements, including junction
capacitances of all semi-conductor devices and the leakage
inductance and magnetizing inductance of the transformer,
are utilized to achieve soft-switching."

Les

currentkills91

Sun Jun 17 2012, 08:06PM

Registered Member #3831 Joined: Thu Apr 14 2011, 02:54PM
Location:
Posts: 265

I used a piece of electrical tape to add a gap between all 3 legs, and it works just as it should, without the horrible oscillating noise. I don't know the top voltage this charger can achieve yet, but it charged a 4400uF cap to the point where the charger was starting to quiet down in about 5 seconds.

The regulator circuit, again, isn't working though, I can never get this circuit to work. I'm using Uzzors2k's 50W charger, and have tried this regulator circuit a few times, and fail to get it to work. While the gates are held low the red LED is lit, when I start charging it goes off and nothing happens from there. I mean it charges, but it doesn't stop like its suppose to. Not too sure what the problem is.

ZakWolf

Mon Jun 18 2012, 07:09AM

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

currentkills91 wrote ...

The regulator circuit, again, isn't working though, I can never get this circuit to work. I'm using Uzzors2k's 50W charger, and have tried this regulator circuit a few times, and fail to get it to work. While the gates are held low the red LED is lit, when I start charging it goes off and nothing happens from there. I mean it charges, but it doesn't stop like its suppose to. Not too sure what the problem is.

I made an old thread about that, i had the same problem. What i did was build the regulator part without the led section, that's where my problem was. also everything is going to a common ground even the caps.

Never got my PCB board to work though :(

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