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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi guys, Is there any practical reason why not to use classical DR-SSTC primary feedback topology (employing CT and Schmidt trigger followed by pair of UCC gate drivers) for induction heaters?
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Current feedback from the inverter output (which is essentially what the DRSSTC topology is doing) works fine for a series resonant induction heater. It just isn't particularly flexible.
For instance you can't achieve power control by detuning the drive frequency as is normally done. An alternative technique like a controlled rectifier, burst fire of the RF drive, or a variac must be used instead.
It also results in the tank circuit being driven at a frequency just below it's natural resonant frequency so there can be some problems with body-diode reverse-recovery transients, particularly if MOSFETs are used.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Thanks Richie, I have more questions… According to your comment it seems is it suitable solution only for series resonant circuit. Why? What if I use parallel resonant circuit and a matched choke in series?
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
There are many CT + schmitt trigger operated PARALLEL RESONANT induction heaters made. Including my ind.heater..:)
Well actually that schmitt trigger is operating as relaxant oscillator to keep it going and to start oscillation. As soon as tank circuit activates, CT signal will override relaxant oscillation and frequency locked operation is acchieved.
Try searching thread named "OMG induction heater for more info".
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Current transformer and Schmidt trigger for induction heater feedback
