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Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Hi all! I was trying to build a new IH for me, since i've already got bored with Mazilli ZVS one. So i created one topic asking about what circuit would be better and easier to build... When "Tonskulus" showed his "schema3" I liked it a lot, so i've decided to follow this schematic, but i've made some modifications because i cant find any powerfull IGBTs near here... And the circuit got this face:
But i'm not certain that everything is alright, and if the IH will work with this schematic, can someone check it and give some clues about it? The circuit is finished, and i have one 12v , 18v and 45v DC supplys for the IH When i turn it on, the only thing that heats up a little is the 40106 IC, the rest keeps cool, seems to be not working and i don't know why... Can you take a look at the circuit and tell if you see something wrong?
I've just noticed that i'll need a Osciloscope for tuning it before the circuit was already finished, and i don't have one osciloscope, so this is a problem, perhaps anybody knows a nice IH circuit that don't need a osciloscope for tuning...? I got only some 630v capacitors for the tank, but i'm trying to turn it up with only 45vDC so i think it can handle for test purposes, the same for the "weak made" coil and small dissipators on the IRFP's The tank of "red" capacitors are de 9uF DC blocking capacitors, can it be this kind of capacitors? As you can see i'm a little confused...
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
First of all, you should check that there is signal on gates of fets. Should be clean squarewave. Again, oscilloscope is nice tool there. However, as you dont have one, you can try this method: -Remove feedback from trigger. -Put Amp meter between powersupply and inverter -Use low voltage for inverter, 24...48V -Now as you adjust potentiometer ( relaxant oscillator frequency), when it hits resonant freq of tank circuit you should see input current rising rapidly. Maximum current means that it is tuned. If there is no change in current at all, something is wrong. Its also possible that Zmatch coil has too much inductance..And I can see that you are using toroidal ferrite core for Zmatch? I think its just too much. You should use EI core with variable airgap.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
oh! ok very nice clues! thank you a lot! i've checked that there's 0,00 Amperage when i put the Amp meter between the inverter and the 41,2vDC Supply, even turning the potentiometer. there's something really wrong... do you have some clues about the oscilator circuit? some readings that i should get? the 12 V+ and GND should go just on VDD and VSS from trigger, or on any other pin of the trigger too? or do you think that the problem is caused by the zmatch toroidal? can i make the Zmatch with a flyback ferrite like this ones?
how many turns do you suggest? and what about the gap?
The IRF's don't warm, the only thing that warms is the 40106 trigger, and the thing don't make any noise one more time, is the schematic that i've posted right?
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
Gabriel35 wrote ...
like on this one? if it's self-oscillating, why does it have one potentiometer? do you suggest some schematic?
i'll try all the way with Tonskulu's schema, if i really can't get nothing from that ill try another circuit...
thank you!
Yes it is self oscillating and not. First of all, it has fixed frequency oscillator so it cant track the resonant frequency of tank circuit. Not very useful and may also lead to mosfet failure if undertuned.
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
yes! because of that I'll keep trying your schematic Toni! What about my questions on 3rd reply? i'm certain that the problem is on my oscilator circuit but i can't find a mistake on that I need that help so i can continue the project
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
you have replaced the max4428 with one cd40106 wich has a much higher output impedance maby if you dubled up on the 5 remaining inveters there would be more drive. If you are interested you could use this chip
and 2 regular n-chanel fets to drive your GDT. the inputs will have to be one from cd40106 pin2 and the other pin4. with this chip you may have to play with phaseing to get it to oscillate. if you need a tool to check this a logick probe will help
Registered Member #2310
Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169
Hey! Now I'm trying the circuit that Karim Ladha developed, using the "same" topology but including a IR2184 MOSFET/IGBT Driver But i need to ask some questions here: That Neutral and LIVE inductors, it is one Zmatch for each wire ? or the Matching inductor goes only in one wire ? (Live or Neutral) and what about the IR2184 Conection Pins, they are not in order on kim's schematic, are them? i've drawed the conection schema as i think it is correct, can someone say if this is right?
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Half Bridge MOSFET Induction Heater Problems
