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Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
Well I'll be either buying a ZVS and building one in a few weeks time, so for now is there a way I can drive these two HOT's I have, I've tried them on 12v but it's nothing, very low output of a light bulb, and no output of a flyback, they're both rated at around 1500v.
I also have a 6A MOSFET driver, whatever that is good for.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Dr. Kilovolt wrote ...
Marko, I have tried the offline driver with HOTs, but they are just so terribly slow (Tstg of around 7us !!) that the waveform gets greatly distorted and the circuit operates inefficiently.
Kilovolt, OMGPIX for me? How did you wire it up and what power throughputs did you get?
The original royers were done with bipolar transistors and a classic circuit is where they are slightly biased to VCC by a pullup resistor, with a feedback sinding going between the bases. This could be a low voltage, high current winding suitable for driving them.
Platinum, in your place I'd try a ZVS with the lowest on resistance mosfets you can find... perhaps even those from PS3 PSU, until you wait for IRFP260's. Run the circuit from current limited 12V so that they don't blow up in case it fails to oscillate.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Hi platinum - how hard can it be to buy some resistors in UK (or just salvage from dead TV's?)
Jan - I've worked out the concept of a HOT royer in my head, simulated it and I think it should work. It could potentially be used for a powerful induction heater.
The truth is that bjt's are far more easily biased into linear region than mosfet's or igbt's, which allows them to be brought into state of max gain easily and not blowing up in case oscillation ceases (just dissipating some power depending on set collector current)
The storage time is also actually a good thing, since it will just prolong the conduction overlap time which is beneficial for a current fed oscillator.
The only big problem is the truly low gain of these devices compared to mosfet's or igbt's, though I believe that a proper feedback winding and network design should alleviate this by providing high loop current gain.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Dr. Pork wrote ...
Jan - I've worked out the concept of a HOT royer in my head, simulated it and I think it should work. It could potentially be used for a powerful induction heater.
The truth is that bjt's are far more easily biased into linear region than mosfet's or igbt's, which allows them to be brought into state of max gain easily and not blowing up in case oscillation ceases (just dissipating some power depending on set collector current)
The storage time is also actually a good thing, since it will just prolong the conduction overlap time which is beneficial for a current fed oscillator.
The only big problem is the truly low gain of these devices compared to mosfet's or igbt's, though I believe that a proper feedback winding and network design should alleviate this by providing high loop current gain.
Marko
I've been toying with a similar idea for a discrete GDT driver, but I've been puzzling over how to implement feedback.
Feedback windings and BJTs might get around this, though.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Yes, a bjt royer uses a feedback winding going between transistor bases - with BE diodes required for low gain transistors.
There was an early version of 2N3055 flyback driver which was basically a push pull royer implemented this way - it lacked a resonant cap though.
Of course, 2N3055's are useless for any serious power throughput. I thought to use some beefy HOT's, such as 2SC3997. They would drive a transformer with a feedback winding and an induction heater tank circuit on the other side. Of course, operating frequency would be low, 20-30kHz at most.
(finally an use for those 100uF eurofarad capacitors?)
Of course some smaller HOT's might work for a flyback driver too.
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
Dr. Pork wrote ...
Hi platinum - how hard can it be to buy some resistors in UK (or just salvage from dead TV's?)
Jan - I've worked out the concept of a HOT royer in my head, simulated it and I think it should work. It could potentially be used for a powerful induction heater.
The truth is that bjt's are far more easily biased into linear region than mosfet's or igbt's, which allows them to be brought into state of max gain easily and not blowing up in case oscillation ceases (just dissipating some power depending on set collector current)
The storage time is also actually a good thing, since it will just prolong the conduction overlap time which is beneficial for a current fed oscillator.
The only big problem is the truly low gain of these devices compared to mosfet's or igbt's, though I believe that a proper feedback winding and network design should alleviate this by providing high loop current gain.
Marko
I've taken apart about 4 TV's in the last few weeks and only lower ohm resistors.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Wow, over the last week a whole bunch of power transformer and power supply threads all the sudden.
a 555 timer with or without gate drive (one transistor, MOSFET or IGBT) is fine for beginners, easy to check with LV. as for ZVS's i dont know, there good for high output current, but seem unstable with variations in load.
Most of the MOSFET deaths with the 555 driver can be avoided with the use of MOV's or TVS's and a gate zener, many new people dont know this though. so in this case the ZVS circuit will be less likely to kill the mosfet then the by the duty cycle adjustment of the 555. that is an advantage of the ZVS over the 555. the ZVS's ive seen,made and scewed with dont seem to output really high HV though. Their mainly good at putting hot arcs out at low kV. i dont have alot of experience with the ZVS's though, so maybe others feel differently.
So, the devices i like are :
---the simple, 555, TL494. new people start here with flybacks and iggies, (no MOTs or NST's til your better at this HV stuff)
---the more complicated, UC3526 and similar, voltage or current mode control, same chip.
---the way more complicated "for HV Aces only!" IC's like the UC28025 or UC28023. with the use of high-side GD IC's your set for any half/full-bridge possibility.
the ZVS's are ok for some fun HV'ing and scewing around, the problem is your always limited by some one elses secondary wire guage, from a transformer you now little or nothing about.
In practice ive run into the "salvaged transformer" limitation long before being limited by the choice of IC vs ZVS. Hence i and others like JPsmith123, and radhoo make our own ferrite wound transformers. driven via IC's and H-bridges, and abandon the common ZVS flyback circuit pretty quick.
Im also going to use ZVS and ZVC modes for the main switches controlled by the 555. This will ease the transistor switching conditions on my next Push Pull Center Tap SMPS, im building now. But it wont use the LC sloshing electricty elements on the primary, and it wont output a sine wave, its all square wave.
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
I actually have experience with HV, but my experience with the circuit driving flyback and that were ready made, like SMPS's, CFL ballast, halogen drivers... That's insulting.
I don't like the arcs from a MOT so I made a high current PSU from it. And NST's are not worth the price, a good flyback can beat an average NST.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Platinum wrote ...
...from a MOT so I made a high current PSU from it. And NST's are not worth the price, a good flyback can beat an average NST.
Yes the MOTs and Variacs have great value since there used to gain both power and perhaps isolation, which then powers all your other many projects, otherwise youll need car battieries (lame) or a PFC AC-DC converter for your house-socket to lab power needs. An IC like the FAN4800 is great, but the MOTs and Variacs are cheap, and not prone to dying easily from bad circuit explosion as SMPS-PFCs semi's are..
a good flyback can beat an NST in some applications and by some measures, i have and use both for different reasons all the time. here is my NST replacement supply...
HV Flyback Bench Top Power Supply for Lab.
However it can depend on purpose. also iggies are more death resistant than the flybacks with their flimsy secondary wire guages.
For example, the 1980's type iggies we Americans call "HEI" or "TFI" are far better than the older common oil-can type iggy. the Oil can type have an "I" core of laminated steel, the HEI//TFI have a double "E" core of laminated steel with a thin gap at the center leg, Cross sectional areas are often 1.5cm^2 or more, while the I cores are often 1cm^2 or less.
the difference in EE vs I cores is magnitising currrent and reluctance, the EE is better in both measures. all of this means the current you put into the primary really does make it to the secondary. with the I core half or less of the current in the primary/main switch makes it to the secondary after initial primary di/dt step up reversal.
The secondaries of any iggy, are generally always supieror in current fusing (not failing due to high arc mA), than any flyback.
These differences in the primary, secondary and core type means the HEI/TFI coils are superior to the common iggies, and any type of Iggy will be harder to kill than any flyback, generally. (provided you dont need power throughtput above 5-8kHz, in the case like a CW, then AC flyback could be made to work, while the Iggies would be lossy if they work at all.)
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Help with Flyback driver?
