Re: 20-60A adjustable ~200vdc current mode buck design

John Barrett wrote:
<osr@xxxxxxxxxx> wrote in message news:1171905102.220242.45790@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
dude, your insane trying to build a 6Kw. lamp supply from scratch,
those lamps blow if ya sneeze.
I know I just blew one trying to build a 2 kW version. I have one
left.

contact bruce @ contact @ second source lasers do com, he has two
eski lamp supplies in stock. BTW the series 6 pins and two connector
bodies you asked for shipped yesterday.

Steve Roberts



Thanks for getting those out, Steve !!

and OF COURSE I'm insane.. even more so than you think because I need 8KW !! (7mm ID bore needing 195-205 volts !!)

However -- the design is progressing -- I've got a model up and running that (without current regulation) stabilizes at a very smooth 48 amps into the tube (presuming 5 ohms tube resistance) after startup... its got a bit more ripple voltage than I would like, and its spiking the AC input hard, but at least I got the soft start and main current path worked out

At this high output current, I would probably thinking about a 2 phase parallel current mode output stage (or pair of stages. This is a fairly simple way to divide the current load equally between two parallel paths, while having something like 80% or 90% of the current ripple cancel. Toy can work with one of the halves, till you pretty much get it working at half current and then build a second one. The trick is to come up with the dual complementary triangle wave to drive the error amplifiers, so that the output pulses are always almost precisely 180 degrees out of phase. I have made fairly high current, low ripple current mode laser supplies this way, though the voltage was much lower, and the load better behaved.

having a real problem with the current sense -- trying to use the switch model to trigger when the ISense voltage passes a preset threshold, but I must have it modeled wrong some how because it is not switching when the tube current spikes.

I think you may need a more continuous current sense, rather than a peak trip.

(I know -- its a kludge, but I'm too lazy to add in the full pwm driver until I got everything else close to working as intended) I'll prolly see what I can do about putting at least a comparator in and see if that helps
.

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