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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
What makes it oscillate? Although I'm great with electronics, I've never dabbled into inductance much. Pretty much all I know is;
It's measured in Henrys It's the resistance to change in an electric current. Iron increases inductance. When mixed with a capacitor it forms an LC tank, the basis of radio. The collapse of a magnetic field in an inductor creates a voltage spike, and this is how some charge pumps work.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Basically, you have the LC circuit consisting of the primary and the 'timing' (actually tank) capacitor which is usually .68uf in the schematics. That determines the frequency of the oscillation. The load on the secondary, if applicable, will vary the primary inductance which changes the resonant frequency, though, that is unimportant.
The two mosfets work in a push-pull topology. The pullup resistors, as the name suggests, pulls the gate voltage up to whatever voltage you have the resistors connected to. This allows mosfet1 to conduct, effectively attaching one 'half' of the primary between the supply voltage. As mosfet1 conducts, it also turns mosfet2 off by connecting one of the fast diodes on the gates of the mosfets to ground, which forward biases it, and pulls mosfet1's gate to ground. As the voltage in the tank circuit peaks, the 'half' of the primary that is flying is at the equal and opposite potential of the conducting half of the primary, which causes the other diode to be reversed biased, shutting mosfet1 off. This means that the other diode will not be forward biased, allowing mosfet2 to conduct. This cycle repeats quickly, giving the oscillations.
I had to go back and change that a few times, so now im not sure if i wrote it how i meant to. I can visualize it clearly, but explaining it is like talking someone into landing a plane over the phone. (please don't mention the Mythbusters)
Registered Member #2591
Joined: Fri Jan 01 2010, 11:58AM
Location: netherlands
Posts: 76
draw it in LT-spice and you see everything, the software is not that difficult.
one thing you have to know is how to couple the coils, this is easy done by edit command line "K L1 L2 L3 1" for example, sometimes it is better to go for 0,9 (software issue) but it works perfect. and give it an "voltage startup delay"
software is for free and you need to learn some hours, and try some things.
it is realy a hint, I have learn a lot about it, and have changed resistor values to get gate drive at 10 volt for a low supply voltage (11.1) volt and power outputt is 200 watts now, without this software I never get it to 200 watt's in practice.
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So how exactly does a ZVS work?
