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Registered Member #1614
Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52
Hi all, Dinges, I had noticed the same waveform in my LCLR IH too when is slightly above resonance. my mosfets haven`t explode yet. I dont know why but I also noticed that this switching transient gets more pronounced when the tank is away from the inverter and matching inductor.
Registered Member #2511
Joined: Mon Dec 07 2009, 02:46AM
Location:
Posts: 36
Hello Hernán,
Good to hear from you. As you can see, I've used your design as the basis for my own, but with some modifications, and weeding out some errors. Nevertheless, was the best design I found on the net - thanks for publishing your works.
In your scope image, it looks as if you're driving the tank circuit below resonance, not above it, from what I can tell, as your 'dirt' is just after the peaks and valleys of the sine, not before. And yes, the hash gets more pronounced the lower your drive frequency becomes, once you are driving the tank below resonance. If you try driving your inverter & tank with a function generator (as opposed to the VCO-out from the 4046), you can play with it yourself and directly see the effect of drive frequency.
Oh, just thought of a way to make the gatedrive perfectly symmetrical: just introduce slightly more delay in the signal path that has less one inverter: slightly increase the resistor from 1k8 to 2k0, or increase the delay capacitor from 100p to 120p (the RC network that in your original schematic is 10k and 1n, in the gatedriver). Changing the timing of one of the signal paths should make the gatedriver waveshape perfectly symmetrical - but doesn't seem worth the bother.
Hernán, have you tried the series topology for driving your induction heater? Your design seems to work fine with it, in my experience.
Registered Member #1614
Joined: Wed Jul 30 2008, 03:08PM
Location: Argentina
Posts: 52
Peter, I`m glad that my schematic was useful to you.
yes, you are right the picture shows that the sinusoidal tank voltage is a bit below resonance.I haven`t got a picture with the tank tuned above resonance but it's similar with your picture. I`ll post it later
yes,it is very good idea to add some delay on the signal path that has one less nand gate to obtain symetrical gate waveform..I need only to change some component values
I meant the workcoil and tank capacitor located some distance away from the inverter & matching inductor. the tank voltage waveform looks worse in this situation.
recently I built a series resonant IH ,with 1.5kw and frq. about 180Khz with PLL control circuit to melt bronze, aluminum and copper . I used other schematic( less components). I'll post it later too
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induction heater project - feedback on inverter.
