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Registered Member #4497
Joined: Thu Apr 19 2012, 12:53PM
Location: Behind you
Posts: 62
The idea is very simple: power tesla coil DIRECTLY by ZVS, and from mains //350V//. i succesfully tested it on 24 volts (got 3cm sparks), but after a while, zener diodes and one "fast" diode (you know which one) died.
my question is: Will 1200V 20A IGBTs survive this torture?
I will try to kill all voltage peaks with some powerful 15V zener diodes. There will be two power supplies, one 12V that will power oscillator and mains that will be fed into primary through choke. I just don't want fireworks at home lol =D Resonant capacitor will be made of 150pF 6300 ceramic caps, hope it won't heat too much.
...And this is just experiment how big sparks will do this quite simple oscillator, IDGAF about some effinency or something, viva la madness!
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
ZVS should be possible with large IGBTs BUT not with the flyback type resonant driver that everybody uses. That is a class e type configuration if I remember correctly. The way to do it with a DR is to have a cap in parallel with the switch so it commutes the current into the cap while the switch is allowed to turn off or on. This results in control of the rise and fall time because the speed of the switch off is determined by the current and the size of the cap.
The flyback type ZVS drive used a lot is going to be very bad at higher voltage because in ordered to protect the gates the zeners will have to dissipate a TON of heat to get the voltage down to 12V from 120V. Although it may be simple it is not suitable for voltage much higher than 40V.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
With the standard ZVS driver, one transistor always connects one end of the capacitor to ground, so a nice half-sine wave like voltage appears on the collector of the other one.
The "zvs" shoud *theoretically* be possible to run from mains with IGBTs, but you must use a separate power supply for the gates.
That said, the gate resistors will need to be small (on the order of 100 ohms or less) to turn the IGBTs ON fast enough at the desired frequency, and also 1200V IGBTs are usually relatively slow parts.
The bottom line is, it might be possible, but only at a low frequency (like 100 kHz). And, the 1200V IGBTs will be stressed voltage-wise with a 325 volt suppy. With a sudden load change, they could be destroyed by overvoltage.
Registered Member #4497
Joined: Thu Apr 19 2012, 12:53PM
Location: Behind you
Posts: 62
Dr. Dark Current wrote ...
With the standard ZVS driver, one transistor always connects one end of the capacitor to ground, so a nice half-sine wave like voltage appears on the collector of the other one.
The "zvs" shoud *theoretically* be possible to run from mains with IGBTs, but you must use a separate power supply for the gates.
That said, the gate resistors will need to be small (on the order of 100 ohms or less) to turn the IGBTs ON fast enough at the desired frequency, and also 1200V IGBTs are usually relatively slow parts.
The bottom line is, it might be possible, but only at a low frequency (like 100 kHz). And, the 1200V IGBTs will be stressed voltage-wise with a 325 volt suppy. With a sudden load change, they could be destroyed by overvoltage.
1.
There will be two power supplies, one 12V that will power oscillator and mains that will be fed into primary through choke.
2. i choosed some IGBTs that have total switch time cca 800ns, which is enough to switch 1MHz 3. they cost $2, so it's not that bad when they die :) i'll try to get some powerful zeners to protect them
Steve Conner wrote ...
Vladi Mazzilli's original ZVS was exactly this, an air cored Tesla coil driven by 1200V IGBTs, running off rectified 220V mains.
The people of 4hv applied it to ferrite-cored flybacks later.
Someone should write something about it on 4HV wiki ;)
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dri0m wrote ...
2. i choosed some IGBTs that have total switch time cca 800ns, which is enough to switch 1MHz
Sorry, but your assumption is wrong. To get a general idea, the total switching time (tdon+tr+tdoff+tf) should not be more than 1/10 of a cycle. For your 1 MHz, the transistors should have less than 100 ns total switching time.
In reality, some circuits work ok even if the switching time is higher (such as the class E topology), but others (such as a hard-switched bridge) require much shorter switching times.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Dr. Dark Current wrote ...
Dri0m wrote ...
2. i choosed some IGBTs that have total switch time cca 800ns, which is enough to switch 1MHz
Sorry, but your assumption is wrong. To get a general idea, the total switching time (tdon+tr+tdoff+tf) should not be more than 1/10 of a cycle. For your 1 MHz, the transistors should have less than 100 ns total switching time.
In reality, some circuits work ok even if the switching time is higher (such as the class E topology), but others (such as a hard-switched bridge) require much shorter switching times.
The two switching delays do not contribute to losses; in a resonant circuit such as a DRSSTC, inserting appropriate forward delays ("Predikter") will compensate for them.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I mite also point out that 800nS is just the thing in there dumb test setup using standard drive value. They can be switched much much faster with a dedicated low impedance gate driver circuit and a higher gate drive voltage like 20 or 24V.
An easy way to get your "real" switching speed is to look at the gate charge graph and get the gate charge for the voltage you plan to drive the gate at. Then use ohms law and the output impedance along with the capacitor current voltage equation and you will find how quick you will be switching.
You could switch at 1MHz but chances are you will need an insane gate drive capable of delivering 10's of amps of drive.
What IGBT are you using? if you link the data sheet I will do an example on how to calculate this for all on 4hv that wish to know how.
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How mad (possible) is this idea?
