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Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi guys, So finally I decided to play with bridge designs. The one introduced in this thread has one important novelty. It employs regular half bridge based on two IGBT transistors IKW25T120 . After DC blocking cap I placed an air cored choke followed by air cored transformer. Secondary of the transformer is feeding LCR resonant circuit, so it means the resonant cap is in parallel with the primary of the coil. Feedback for the coil is taken from the secondary using current transformer.
Video - the coil is running in CW at 170Khz
I’ll prepare complete schematics soon…
Cheers, Mates
On the picture below you can see the air cored choke (black) and transformer (white)
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Dr. Kilovolt wrote ...
But what is the purpose of the isolation transformer?
Ok, You right that the isolation transformer could be skipped… There are two reasons why I started to experiment with such approach. The first is the IGBT protection. I think the bridge is much safer being isolated by transformer.
The second reason is something I wanted to reveal after I will try it, but why not to discuss it before. I prepared the scheme below to make my idea clear. As you maybe noticed the transformer is trifilliar. My plan is to use one of the secondary windings to be discharged into the main smoothing capacitor over very fast diode bridge using transistor. The transistor can be driven by any kind of modulated signal (e.g. PWM). In other words it is just an idea for PWM audiomodulation while keeping the resonant frequency of the coil driven by feedback and also kept the half bridge in the zero voltage/current mode.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi, I tried the audiomodulation as suggested above and it doesn’t seem to be very practical approach. Problem is that the main smoothing cap needs to be undercharged otherwise the sound cannot be heard. It means some additional current limiter between mains and the cap. Even with the current limiter it sounded like crap so I’m leaving this idea as the blind way…
On the other hand I played with the system a lot. It proves to be quite bulletproof. I can draw nice ground arcs which are very silent.
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Mathias wrote ...
Why not try it with a seperate capacitor (with a parallel resistor) ?
Of course one of the transformer secondary can be simply shorted via resistor (you don’t need any parallel cap for that). But that means horrible power loss which I wanted to refrain by sending the energy back into the system.
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My new half bridge
