Quote from: davekni on January 12, 2023, 03:56:33 AM

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The way I built it is pretty much exactly the same but with irfp460 MOSFETs.

With FETs instead of IGBTs, I'd recommend using a 1:1 GDT.  Can be made with much lower leakage inductance (by winding with two twisted pairs and paralleling one wire of each pair for primary).  Also reduces load on driver chip.

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Another main difference is that I got impatient with the whole ground plane thing and just connected the base of the secondary directly to the antenna. I theorize that this might be the issue. I wonder if inverting the schmitt trigger might solve this and let me keep getting away with the direct secondary feedback. What do you think?

Feedback from secondary bottom is used by other coils (including my SSTC).  Secondary peak current is likely to be 1-2A.  A bit high for 1N4148 diodes even at low duty cycles.  Also can cause an issue of over-powering +5V supply.  Diodes feed current to +5V, more than circuitry consumes.  All designs I've seen using secondary feedback either use a current transformer (CT) or use high-power zener or TVS diodes to clamp voltage rather than clamping to +5V.  (Additional lower-power clamp to +5V may exist after series resistor limits current.)  If you decide to use a current transformer, clamping needs to be symmetric around 0V and/or AC-coupled before clamp.  Otherwise DC component of voltage will saturate CT core.

Good grounding is still necessary.  With secondary bottom feedback, grounding of logic supply negative rail becomes the most important.  At least connected to line ground.  Counterpoise is better.

Yes, polarity may need inverting when changing from antenna to secondary feedback.  This can be done by swapping GDT primary wires or SSTC primary wires or by adding an inverter stage.  You'll just need to try both polarities to see which works.

Adding bleed resistors across 0.82uF caps or across IGBTs can help with startup.  Makes sure that initial state of half-bridge output is centered so that initial half-cycle will generate some feedback.  A resistor across only one side can be better or worse depending on which IGBT turns on first, which is nondeterministic with this circuit.  My favorite fix is to add a resistor from HC14 pin 2 to far side of 1k resistor (junction of 1k and 0.1uF).  That keeps the HC14 toggling even when coil is off (between interrupter pulses).  There are some other threads here discussing this change.  Details for your case depend on what other changes you make first.

Good luck!

Wow, this all sounds like great advice. I can see why adding that resistor to the HC14's pin 2 is your favorite, it sounds brilliant and I don't know why I didn't think of that myself. I'll give all that a try, thanks.

use an antenna. Im pretty sure that will solve your problem

here is the output from the 74hc14

Hi

I am starting to think that my board works fine because this is how the input signal looks.
(I was probing where the antenna is supposed to be connected)

Hi. I'm building a tiny staccato ramped QCWDRSSTC. I calculated everything in javaTC and exported it as text:

J A V A T C version 13.6 - CONSOLIDATED OUTPUT
11.10.2022 14.09.07

Units = Centimeters
Ambient Temp = 20ºC

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LINEAR
3.75 = Radius 1
3.75 = Radius 2
0 = Height 1
8 = Height 2
760 = Turns
0.01 (cm)= Wire Diameter

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
5 = Radius 1
5 = Radius 2
0 = Height 1
1.39 = Height 2
4.635 = Turns
0.1(16A Rated. Intalation cable) = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.05 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
363.13 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
8 [cm] = Length of Winding
95 [cm] = Turns Per Unit
0.00526 [mm] = Space Between Turns (edge to edge)
179.07 [m] = Length of Wire
1.07 [:1] = H/D Aspect Ratio
389.88 [Ohms] = DC Resistance
65908 [Ohms] = Reactance at Resonance
0.013 [ kg] = Weight of Wire
28.886 [mH] = Les-Effective Series Inductance
29.057 [mH] = Lee-Equivalent Energy Inductance
28.127 [mH] = Ldc-Low Frequency Inductance
6.65 [pF] = Ces-Effective Shunt Capacitance
6.611 [pF] = Cee-Equivalent Energy Capacitance
12.131 [pF] = Cdc-Low Frequency Capacitance
0.1195 [mm] = Skin Depth
4.61 [pF] = Topload Effective Capacitance
756.6971 [Ohms] = Effective AC Resistance
87 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
363.14 [kHz] = Primary Resonant Frequency
0 [%] = Percent Detuned
90 [deg °] = Angle of Primary
145.61 [cm] = Length of Wire
31.96 [mOhms] = DC Resistance
0.2 [cm] = Average spacing between turns (edge to edge)
1.195 [ cm] = Proximity between coils
0 [cm] = Recommended minimum proximity between coils
3.858 [µH] = Ldc-Low Frequency Inductance
0.05001 [µF] = Cap size needed with Primary L (reference)
0 [µH] = Lead Length Inductance
124.27 [µH] = Lm-Mutual Inductance
0.377 [k] = Coupling Coefficient
0.126 [k] = Recommended Coupling Coefficient
2.65 [half cycles] = Number of half cycles for energy transfer at K
3.32 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=2, major=14.3, height=11, topload

Am i missing something obvious?

A few recommendations:

ICs generally need bypass capacitors from power to ground.

Switching IC power directly from another IC output is problematic once bypass capacitors are added.  No need for such.  The reset pin is sufficient for your logic needs.

Not sure if there are any convenient NE555 models for LTSpice.  However, I suggest simulating at least the power switch (Q3) using a stepped voltage source to simulate output of U5.  Look at NE555 specifications to see the output Voh level, typically about 1.3V below VCC.  Use that voltage for stepped voltage source.

BTW, is there any reason for the ZVS oscillator to remain on after fan turns off?  I'm just wondering, depending on how your device is intended to be used.

I simulated both the entire zvs circuit and the fan controller in LTSpice, and everything worked as it should. the 555 can output 200ma, so it should be more than enough to drive both the other 555 and the MOSFET. I am considering adding a push-pull amp to Q3 though or maybe a dedicated driver ic and signaling into that via the 555.

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I designed a NE555-based circuit that eliminates all the startup problems

Sounds interesting.

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Something weird I noticed though. Why is the voltage of the blue waveform so much higher?

No way to know without seeing circuit and a zoomed-in view of final higher-voltage oscillation plot.

I thought the rise at the end was weird so I ran it again and got the exact same result but without the bump. It was just some weird anomaly. I am designing the final schematic tomorrow and will post it here. It would be really nice if you would take a look at it, and tell me if I did something weird/stupid .

Hi

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If you center-tap the transformer primary, the two 50uH inductors can be replaced with one smaller inductor from center-tap to 12V supply.

I know, but it is simpler to measure and troubleshoot.

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Do you have the option to turn on the 12V supply to gate resistors (460 ohms in your schematic) before power to inductors?

Yes, but it would have to be done automatically and quickly. Could an RC Time circuit and MOSFET get the job done?

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460 ohms seems high for 12V input.  Is that copied from higher-voltage units?  At 12V, lower resistance will provide enough current for fast FET switching.  I'd try ~100 ohms.  Will still be under 1W each during operation.

I have used 460 ohms before, all the way from 16 to 36 volts input. I will probably change it to a lower value. 470 does seem like a lot.

Thanks

Hi!
 
I am building a device for a national competition ("Unge forskere") That should be able to sterilize hands with nothing but electricity.

For this project, I need a High-Voltage power supply, capable of delivering 12(or so)kV at 30-100khz.
Therefore my head automatically went to the very popular "ZVS driver" because I want a very efficient operation without much heat as it will be placed in a closed box.
You can look at my current schematic in the attached picture.
I modeled the schematic in lTSPICE and found that 71v spikes occur at startup, and therefore can't use the 60v IRFZ44N I originally wanted to use.
Now the problem is that I don't know what other MOSFET I can use.
I don't care if it is SMD or THT.
I found a few FETs I think will work, but I'm not certain
https://www.mouser.dk/ProductDetail/onsemi/NTP011N15MC?qs=DPoM0jnrROX1k1aAlpufTw%3D
https://www.mouser.dk/ProductDetail/onsemi-Fairchild/FDP085N10A-F102?qs=0lQeLiL1qyaFktU8QMby%252BQ%3D%3D
https://www.mouser.dk/ProductDetail/Infineon-IR/IRLR3110ZTRPBF?qs=Z8%252BeY1k3TILcI4snfu078g%3D%3D

Any help, both with MOSFET choice and flaws in my design are greatly appreciated

Hi

I am building a relatively large SGTC and made a stupid mistake while calculating the resonant frequency.
I stupidly forgot to add the topload to javatc, and calculated the whole thing as if the top load didn't exist.
Is there a way to raise the secondary's resonant frequency enough to add a small top load?
I could of course just add some more primary turns, but I spend a lot of time making a good-looking primary and would like it to stay as it is now.
I'm feeding the coil 2.1 kw

Is it possible matching the primary and secondary frequency without adding more than a few primary turns or changing my(too small I know) capacitor?
Do I even need the top load in the first place?
All help would be much appreciated!

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I am thinking of making a dual mot sgtc, and therefore i need capacitors.

MOTs are particularly dangerous:  Enough voltage to arc through clothing with current capability several times lethal threshold.  NSTs are much safer, generally limited to 60mA or less, so much less likely to be lethal if you make a single mistake.  I have a dual-MOT SRSGTC, but rarely set it up because I'm too afraid of making a mistake.

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I am aiming for slower arcs of around 150 bms. So my max capacitance becomes 95nf.

That is rather low power for two MOTs.  6kV on 95nF is 1.71J, or 257 watts at 150 BPS.  Two MOTs are capable of 2kW (or more for intermittent use).  My coil runs at 120 BPS with ~700nF and resonant charging to 9kV.  Of course, if you have two MOTs in hand, that's cheaper than purchasing anything safer for 257 watts.

Your first link to 0.33uF 1200Vdc induction cooker capacitors looks like roughly the same parts I use in my DRSSTC and have ran some destructive testing to 2100Vpk (4200Vpp) at 80kHz 1% duty cycle.  Your third link labeled "VERY CHEAP" would require 4 times as many parts for the same final Vdc rating and capacitance, since they are only 630Vdc rated.  Would likely work fine, though I have no experience with these.

Have fun, and experiment safely!

I only felt safe enough to build it because a am doing it with two friends.

I think of using the cheap caps because I can distribute the load across 80( or so) caps.