Power Supply: Voltage double and regulated source

I need to talk about two power supplies for the unit. One is the high voltage DC that the inverter converts to AC for feeding the tank. You need an unregulated, smoothed source. You can use 110vac through a rectifier and smoothed with a 1000uf-1500uf capacitor for a supply of 170vdc. I used a voltage multiplier to convert it to 320vdc. Below are some basic schematics for a voltage doubler. I used the third variation for mine. Make sure you have your rectifier on a large heat sink because it will be conducting a lot of amperes. My rectifier is rated for 25A/500vac.

When I transitioned to my 10kw unit I increased the size of my high voltage supply. Each capacitor is rated for 450vdc, so I can go up to 900vdc between both ends. I use two 50A rectifiers giving me 100A.

The second power supply you will need will be a 15vdc regulated source. It is imperitive that it is regulated because the PLL has a voltage controlled oscillator. The VCO determines the output frequency based on input voltage it receives. The frequency range it can generate is based on its supply voltage, Vss. If the supply voltage wanders, the oscillator frequency will wander and this will definitely throw you out of resonance.

Now, when I made the 10kw unit it uses four mosfets instead of two. This is twice the amount of gate charging. You need to make sure your 15vdc supply can supply the amps to rapidly charge the gates. It should also have a robust transformer and capacitor on the end to make sure there is plenty of charge available. I plan on adding an outboard pass transistor. One problem that plagued me for the longest time was a jittery inverter current when I reached modest power levels. The current would jump back and forth when compared to the inverter voltage. It appeared as if two currents were competing. At first I thought this was EMI affecting my gate drive and I spent the longest time trying to fix it. I noticed that when I disconnected any one of the four mosfets the current tracing was perfect. This led me to believe that I was falling short on charging all the gates rapidly enough, and the mosfets were not all conducting identically. Remember, you need to fully turn the mosfets on in the shortest time possible. I put a scope on the gates and noticed that the slopes changed when I added the fourth gate. I solved the problem by adding a 39000uf capacitor to my power supply. This was with a 1.6A transformer and a 2A 15v regulator. The tracing was perfect. I plan on changing the transformer to 3A and adding adding the outboard pass transistor just to play it safe.


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