Since initial tests of almost-RF drive for ion source and main grid were pretty successful and interesting... I thought I'd do some "product improvement" on the power supplies for these.
Here I'll just talk about the one for the main grid, the coil shown in "recirculation". Based on what I saw there, I need more speed - and more volts. Sadly, more volts also means needing more speed if any of the math is right...but we are just going to creep up on this as I can put the required tools together - this stuff ain't found on street corners.
To get to the hundreds kHz, and hopefully a good bit more voltage, I've acquired a couple of bigger bulk DC power supplies - 30v @ 10 amp each, planned to be in series, and computer controlled at some point, but for now, I just added reverse polarity protection diodes and a path to ground for the lower one in case of arcs.
To use this ~ 60v at ~10 amps - which is getting back to real power...I need a better H bridge and driver than the ones based on the IRS2453 simple circuit with it's own built-in high side drivers. Not only is it limited to around 90kHz - those fet drivers are much too wimpy for the IRFP-264 fets I want to use here.
So, I'm going with a good old LM 3524 to create push pull square wave drives at variable frequency up to almost 500khz and some horsey fet drivers and using transformer coupling for the high side, since these drivers can't do that without some help. I copped a pretty neat trick from an old Glassman power supply I parted out, which I'll have to draw and attach - it uses a pnp darlington transistor for turnoff of the high side FET which can get it done a lot faster than the current that will come through the transformer - the "power supply" in this case is the gate capacity itself, charged up when the thing is on (and the miller capacity too).
As you can see, it's kind of a mess on my bench here - I just fixed up one half of the drivers while I worked on drive waveform quality - I did do some short tests with full volts on the fets to see the miller capacity issues - they're there, but not too bad, this drive scheme is a bulldozer.
I tried two transformer types - the toroidal one is parted out of an old Glassman power supply, and is ~ 1.5mh windings. The other one is ~ 2mh windings, a little bit thinner wire. I went with the former, for the slightly fatter wire and less need of insulation anyway in this voltage range - the other ones will be used with *real* high voltage fets later. It wasn't a huge difference, but at an amp or more peak current, you could see the series R.
The blue and green traces are the outputs from the LM3524 chip (in this case, the emitters as we're using non inverting gate drivers).
Yellow and violet are the low side fet gate and the high side one respectively. There's a little attenuation and slowing in the high side one, but it'll do. Part of the attenuation is those diodes forward drop. The transistor shown below *dramatically* cuts the turn off time, even more so when there's actual supply for the fet D<>S and there's miller capacity to deal with.
Sadly, if I want to go a lot faster, it looks like I'm in the "make your own drive source with deadtime to drive the driver" land. Unless someone knows of an IC a lot faster than an LM3524. This one's at its rated max, or close.
The final drive for the high side:
I have a parallel project going with an ESP8266 and an MCP4631 dual i2c potentiometer to control this remotely. More on that when there's more. For now, knobs.
Some data sheets: