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Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Davebmx wrote ...
sorry did you mean like this?
regards
Dave
This is not right, see the attached schematic, taken from . The rectifier is drawn wrong in the application note, but otherwise it's correct
Davebmx wrote ...
Hi Kolas!
been through Mr Burnetts page many times haha! he does say that aslong as the frequency is on the high side of resonance it should only cause loss of power or for the whole thing to drop out of resonance but i am having catastrophic failure of the igbt?
That's true for the LCLR or series resonant induction heaters driven from a half- or fullbridge, but not for this quasi-resonant circuit we're discussing here. For the quasi-resonant circuit, it is generally very important to have¨close to zero voltage switching at all times. The application note I linked shows some example waveforms. This type of induction heater is generally very easy to kill when operating open-loop from an oscillator.
Registered Member #4394
Joined: Mon Feb 06 2012, 07:43PM
Location:
Posts: 40
thankyou Wolfram that is an excellent source¬
so, if i stick to my initial circuit sans the dodgy rectifier drawing i am in the right direction? I have the oscillator coded to an 8 bit chip as i have always planned to integrate feedback resonant control later on. To add this function however i would need to know what i should be measuring and also where to measure it from. I'm assuming i would need to measure it directly from the work coil through a large value resistor but how do i find the resonant frequency if i cant get the circuit to run without the feedback initially to get my baseline figures?
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Linas wrote ...
I like this circuit, it should heat up quite fast :D (complete short circuit)
Yeah, I noticed that, I almost commented at the time. You would have thought Fairchilds' QC would have picked that one up before it was published. It should be a bridge rectifier like in the other diagrams in that PDF.
Registered Member #4394
Joined: Mon Feb 06 2012, 07:43PM
Location:
Posts: 40
This circuit is proving to be a real pain!
I have the square wave oscillator working well so i was hoping someone might have a good schematic for a mains powered induction heater similar to this but easier to get working? Something of a half wave topology that will be a bit more resilient to frequency change?
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Induction heated nightmare
