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Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Awhile back i decided i wanted to make a general purpose Royer oscillator that was even more efficient than Mazzilli's schematic. It works the same, but it utilities a dual gate driver to give the gates a square signal instead of the 'sine' waveform it normally sees. This lowers switching losses even further.
I made the PCB, but i never printed it. Then recently, i saw the Royer induction heater made by 'Neon John' ( ) and decided to adopt the NAND gates to insure both mosfets may never turn on at the same time. It turned out to be pretty close to . I omited the 10K pulldown resistor on the gates, as well as the zener. For the NAND i used a 7400, and the mosfet driver is a UCC27324. After i added that, i made the PCB.
I hooked the driver up to a flyback, and tested it at 24v. It oscillated fine, and the gate waveforms where nice and had minimal ringing. Nothing heated, either. But, as soon as i ignited an arc, the circuit stopped oscillating, and one of the mosfets would be held on and would short the supply through half the primary.
I tried numerous different transformer combinations. The one i found that worked best was a U core transformer with .5+.5:1 ratio, and a small work coil for induction heating. It pulled about 200 watts, and the IRFP460's stayed cool with no heatsink, but if i inserted a piece of metal that presented too much of a load, the same thing happened. All tests where done with a .5uf cap tank cap and about 100 turns of quad-filar 24 gauge on a 2 inch ferrite toroid for the input inductor.
I have never had this happen with an all discrete Royer (The Mazzilli circuit), so i think it has something to do with either the NAND gate or the driver. I am leaning toward the NAND gate. I will attach a screenshot of the .pcb file just in case it helps. The tank caps are actually on the bottom of the circuit board, for the record.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Arcstarter wrote ...
Awhile back i decided i wanted to make a general purpose Royer oscillator that was even more efficient than Mazzilli's schematic. It works the same, but it utilities a dual gate driver to give the gates a square signal instead of the 'sine' waveform it normally sees. This lowers switching losses even further.
I made the PCB, but i never printed it. Then recently, i saw the Royer induction heater made by 'Neon John' ( ) and decided to adopt the NAND gates to insure both mosfets may never turn on at the same time. It turned out to be pretty close to . I omited the 10K pulldown resistor on the gates, as well as the zener. For the NAND i used a 7400, and the mosfet driver is a UCC27324. After i added that, i made the PCB.
I hooked the driver up to a flyback, and tested it at 24v. It oscillated fine, and the gate waveforms where nice and had minimal ringing. Nothing heated, either. But, as soon as i ignited an arc, the circuit stopped oscillating, and one of the mosfets would be held on and would short the supply through half the primary.
I tried numerous different transformer combinations. The one i found that worked best was a U core transformer with .5+.5:1 ratio, and a small work coil for induction heating. It pulled about 200 watts, and the IRFP460's stayed cool with no heatsink, but if i inserted a piece of metal that presented too much of a load, the same thing happened. All tests where done with a .5uf cap tank cap and about 100 turns of quad-filar 24 gauge on a 2 inch ferrite toroid for the input inductor.
I have never had this happen with an all discrete Royer (The Mazzilli circuit), so i think it has something to do with either the NAND gate or the driver. I am leaning toward the NAND gate. I will attach a screenshot of the .pcb file just in case it helps. The tank caps are actually on the bottom of the circuit board, for the record.
I can see the problem right away. The NAND gates need to be schmitt trigger ones, otherwise they may float in indefineable states, which might be what's causing your problem.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I have succesfully built an "active feedback" version of this driver, it uses a 74HC14 (oscillation start and feed back) and two gate drivers. The feedback is based on a feedback winding rather than the problematic diode feedback. If anyone is interested I can post a schematic tomorrow.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Dr. Kilovolt wrote ...
I have succesfully built an "active feedback" version of this driver, it uses a 74HC14 (oscillation start and feed back) and two gate drivers. The feedback is based on a feedback winding rather than the problematic diode feedback. If anyone is interested I can post a schematic tomorrow.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Dr. Kilovolt wrote ...
I have succesfully built an "active feedback" version of this driver, it uses a 74HC14 (oscillation start and feed back) and two gate drivers. The feedback is based on a feedback winding rather than the problematic diode feedback. If anyone is interested I can post a schematic tomorrow.
That is funny, i just made a new royer with a gate driver, and instead of a NAND, i used a 74HC14, mostly due to the fact that i only have inverting drivers, but it will also ensure a good signal. So, i guess it is like yours, but with the diode feedback scheme.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
It's hard to tell without a schematic, but do you have diodes to keep the feedback into the gates from going above Vcc or below Gnd? Also it looks like you have some unconnected gates in the package, that's a bad idea. Unused inputs should always be tied to either Vcc or Gnd, otherwise you can get spurious oscillation that can affect the portions of the IC that you're using. Don't forget bypass capacitors across the power rails of each IC either.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
James wrote ...
It's hard to tell without a schematic, but do you have diodes to keep the feedback into the gates from going above Vcc or below Gnd? Also it looks like you have some unconnected gates in the package, that's a bad idea. Unused inputs should always be tied to either Vcc or Gnd, otherwise you can get spurious oscillation that can affect the portions of the IC that you're using. Don't forget bypass capacitors across the power rails of each IC either.
There are unconnected gates, but i soldered on a small piece of copper wire to the unused pins and grounded them. Whats the point? I don't know I always use bypass capacitors. In my days of breadboarding i realized just how terribly logic performs when there are no bypass capacitors.
Registered Member #4254
Joined: Sat Dec 10 2011, 09:36PM
Location: Dhaka, Bangladesh
Posts: 27
Dr. Dark Current wrote ...
I have succesfully built an "active feedback" version of this driver, it uses a 74HC14 (oscillation start and feed back) and two gate drivers. The feedback is based on a feedback winding rather than the problematic diode feedback. If anyone is interested I can post a schematic tomorrow.
Hey i was working on a ZVS induction heater and um veru much excited to see your circuit!!
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Improved Royer Oscillator Problem.
I always use bypass capacitors. In my days of breadboarding i realized just how terribly logic performs when there are no bypass capacitors.
