Yes.Does the OSC set the KHz of the Flip Flop?
Forcing the load coil to run at 100 KHz all the time does that not interfere with the resonance frequency of the RC circuit?
Does the circuit not need to run at the resonance frequency?
My mosfet circuit runs at 89KHz with no load. With a 3/8" solid steel rod in the coil frequency drops to 64KHz.
POST ISSUE 02 of 2016_11_09
Gary, it seems to me that there are two good approaches for your induction heater:
(1) Full bridge: four MOSFET/IGBT
(2) Half bridge with +- supplies: two MOSFET/IGBT
I think (2) has a lot of benefits so, for your consideration, I knocked out a quick block diagram to illustrating the approach using a single UCC21520 chip and two high power MOSFET/IGBT:
I have been a bit lavish with the 15V power supplies, and while two are not absolutely essential, they do give complete isolation between the logic and bridge. They also improve performance and make the operation of the circuit easier to understand. And PSUs are dirt cheap on the net anyway.
spec
This diodes still do not look right to me. With the diodes like they are it produces a pulsing DC wave. I though an induction heater worked by changing the magnetic field, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, N, S, at 100KHz?
**broken link removed**
in the 12v zvs....
I found that the resonant frequency of the coil changes under load, frequencies run higher and less current is drawn when there is nothing in the coil... something like 1/4- 3/4 amp.
but under load , the res frequency goes down and current goes up... to like 5 amp... and you really hear the coils work(although it could have been my bad choke mentioned below)
and as the material gets hotter frequency rises a bit to maintain synch to the load. Because with the heat atoms become looser to spin
Also i should mention i had to put a choke on my power supply line as per the schematic, but i ended using one that wasnt big enough and allowed enough power spikes to travel back and damage my 14v 7A power supply(it now puts out 24v for some reason) ,
Also capacitors were added parallel to the work coil which also brought the current up more.
the 12v zvs was run by fast avalanche diodes cross connected to the gates ... in the Larger driver , they used a PLL, current detection coils, and optical isolation... also it had a microcontroller override (which I was told it was for a "soft start up", but did not have a chance to investigate in detail)
idk if these are problems or not for this design, just mentioning my experience to shed some light.... hope this helps a bit!
in the 12v zvs....
Also i should mention i had to put a choke on my power supply line as per the schematic, but i ended using one that wasnt big enough and allowed enough power spikes to travel back and damage my 14v 7A power supply(it now puts out 24v for some reason) ,
!
I had a power supply problem when I first built my circuit too. Sometimes the capacitors blow up, sometimes the rectifier blew up. I changed the choke coils several times but in the end I decided RF was killing the 3300 electrolytic capacitors. I put a small ceramic .001 uf cap in parallel with every electrolytic capacitor that stopped the problem. The rectifier problem was the manufacture error they claimed bridge rectifier was rated 100 amps but test show they were not good above 20 amps. Power Supply has 12 caps 3300 each in parallel = about 40,000. Tests show Power Supply voltage is 21 VDC, the RF voltage is 70 volts on the same wires.
Great board.There is a UCC21520 module available all that is required is attach 2 wires from the 15v 4a DC power supply then run 2 wires from each output to each IGBT. There is an adjustment for dead zone time. I dont see an OSC and it says nothing i see about an OSC imput.?
With just 40,000uF toat capacitance you would have a huge ripple voltage on the capacitors which would not be good for the capacitors or the power output of the induction heater.
Wouldn't metal film caps like a MKP type of something similar to them be more appropriate for this application?
Wouldn't metal film caps like a MKP type of something similar to them be more appropriate for this application?
MKP (metal film polypropylene) would make fabulous reservoir capacitor but, by god, that would be a big expensive power supply
Hi SB,I don't know about expensive. I've bought some for my EDM circuit and they weren't that bad price wise. But they were from an electronics surplus place. When you want something to work and spend time blowing up unsuitable components, doesn't that add up? Buy what is correct once and your ahead of the game, or at least that's my way of looking at it. But then again I'm just a rank newbie at this stuff.
Just following along in this post and the others he's made about the same topic over time, I'm finding it hard to believe that he really made the Tesla coil he was trying to sell a few years ago. An induction heater is hard but not on the order of a Tesla coil. And if I remember correctly he claimed to have built that.
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