HFSSTC
Simone, Mon Apr 24 2017, 10:44AMHi, I'm new here.
I'm trying to build a HFSSTC following the project of richie burnett (
and from this other guy (here I think i have enough driving power for the final irfp460 mosfet (i'm probing at the 460 gate)
...but as i apply power to the drain (i tried with voltage from 15 to 70v DC) i get this
(the probe is again to the gate).This is the scheme i've followed
I searched with an air variable capacitor (500pF) the "optimal value" for the unspecified cap (should be someting arounf 330pF) but with no luck.
So... i don't know how to fix this problem...
Re: HFSSTC
kilovolt, Wed Apr 26 2017, 09:26AM
Hello Simone
Welcome to the forum.
The second link is from my page. You should remove the bracket at the end of the link for let it working correctly
Your problem can have several different causes. For me it seems your circuit works okay up to the gate of the powerfet, but it looks like your final stage is getting out of the class-e mode when powering it with low voltages. This happens with my coil as well. My coil doesn't work correctly with too low voltage. It needs about 120V. Below that voltage it starts to sizzle angry and the powerfet is getting hot. Have you got an ajustable power supply for your coil?
You may also try to change the coupling between primary and secondary a bit (lower or rise the primary a bit). Sometimes it needs a bit trial and error before working properly.
Best regards
kilovolt
kilovolt, Wed Apr 26 2017, 09:26AM
Hello Simone
Welcome to the forum.
The second link is from my page. You should remove the bracket at the end of the link for let it working correctly
Your problem can have several different causes. For me it seems your circuit works okay up to the gate of the powerfet, but it looks like your final stage is getting out of the class-e mode when powering it with low voltages. This happens with my coil as well. My coil doesn't work correctly with too low voltage. It needs about 120V. Below that voltage it starts to sizzle angry and the powerfet is getting hot. Have you got an ajustable power supply for your coil?
You may also try to change the coupling between primary and secondary a bit (lower or rise the primary a bit). Sometimes it needs a bit trial and error before working properly.
Best regards
kilovolt
Re: HFSSTC
Simone, Wed Apr 26 2017, 11:17AM
Well it's nice to be welcomed directly by you!
I have a transformer with many output so I tried with 100v.but the waveform at the gate is still a mess... Tried with almost any cap value(and with the variable cap too) , I tried varying the turns of the primary but nothing seems to work. Maybe my FET is damaged and I'm losing time but I don't know what else to try
Thank you for your time!
Simone, Wed Apr 26 2017, 11:17AM
Well it's nice to be welcomed directly by you!
I have a transformer with many output so I tried with 100v.but the waveform at the gate is still a mess... Tried with almost any cap value(and with the variable cap too) , I tried varying the turns of the primary but nothing seems to work. Maybe my FET is damaged and I'm losing time but I don't know what else to try
Thank you for your time!
Re: HFSSTC
kilovolt, Wed Apr 26 2017, 01:07PM
Simone, what kind of oscillator have you got in your setup? Is it a quartz with fixed frequency or is it a 4046 PLL or something similar with variable frequency? If you've got a quartz, the secondary coil is critical. The resonance frequency of the secondary coil has to be a bit higher than what the actual quartz frequency is, because the flame will lower the frequency a bit and then pulls the coil in tune. If you've got a variable oscillator, it is much easier to find the optimal tuning point.
Best regards
kilovolt
kilovolt, Wed Apr 26 2017, 01:07PM
Simone, what kind of oscillator have you got in your setup? Is it a quartz with fixed frequency or is it a 4046 PLL or something similar with variable frequency? If you've got a quartz, the secondary coil is critical. The resonance frequency of the secondary coil has to be a bit higher than what the actual quartz frequency is, because the flame will lower the frequency a bit and then pulls the coil in tune. If you've got a variable oscillator, it is much easier to find the optimal tuning point.
Best regards
kilovolt
Re: HFSSTC
Simone, Wed Apr 26 2017, 01:12PM
Crystal osc + some small transistor then CD4093.. I measured the coil and it resonates at something like 100kHz below (4.21 MHz) the freq of the crystal.
Simone, Wed Apr 26 2017, 01:12PM
Crystal osc + some small transistor then CD4093.. I measured the coil and it resonates at something like 100kHz below (4.21 MHz) the freq of the crystal.
Re: HFSSTC
kilovolt, Wed Apr 26 2017, 01:26PM
That may be a problem. I would remove a few windings until the resonant frequency is a bit higher than the crystal oscillator frequency. Together with the arc, it will pull the resonant frequency to the osc.-frequency.
kilovolt, Wed Apr 26 2017, 01:26PM
That may be a problem. I would remove a few windings until the resonant frequency is a bit higher than the crystal oscillator frequency. Together with the arc, it will pull the resonant frequency to the osc.-frequency.
Re: HFSSTC
Simone, Thu Apr 27 2017, 09:02AM
I've removed some wire so now the resonant frequency is 100 kHz above the crystal freq. I've also replaced the FET (with a new one) and the waveform at the gate it's changed very much... as soon as i can i'll post some shot. so i think that maybe the previous FET was effectively damaged and the gate driver wasn't properly tuned.
Simone, Thu Apr 27 2017, 09:02AM
I've removed some wire so now the resonant frequency is 100 kHz above the crystal freq. I've also replaced the FET (with a new one) and the waveform at the gate it's changed very much... as soon as i can i'll post some shot. so i think that maybe the previous FET was effectively damaged and the gate driver wasn't properly tuned.
Re: HFSSTC
Simone, Fri Apr 28 2017, 12:35PM
Ok.. so.. after changing the FET i've rewound the second GDT to make it work properly and now everything is fine!
So... thank you!
PS : kilovolt, did you try audio modulation?
Simone, Fri Apr 28 2017, 12:35PM
Ok.. so.. after changing the FET i've rewound the second GDT to make it work properly and now everything is fine!
So... thank you!
PS : kilovolt, did you try audio modulation?
Re: HFSSTC
GeordieBoy, Mon Sept 04 2017, 02:47PM
You ideally want about +/- 15 volts on the gate for good clean Class E switching. If your gate voltage is only just making it to +10V with no B+ applied to the final power stage, the amplifier might go unstable from insufficient drive when you apply B+ to the MOSFET drain. Definitely better to drive it a bit harder.
-Richie,
GeordieBoy, Mon Sept 04 2017, 02:47PM
You ideally want about +/- 15 volts on the gate for good clean Class E switching. If your gate voltage is only just making it to +10V with no B+ applied to the final power stage, the amplifier might go unstable from insufficient drive when you apply B+ to the MOSFET drain. Definitely better to drive it a bit harder.
-Richie,
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