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Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
Seeing as we're on the topic of driving fast bricks with a UD controller, I thought it was about time to make my first post.
I recently got 5 SKM200GB125D "ultra-fast" bricks for free (!!), and am looking at whether they'd be capable of running at QCW coil frequencies using a UD 2.5 phase-lead controller (or possibly a 4046 based PLL in the future). Obviously they aren't as fast as good mini-bricks, but the specs seem rather good for a brick (td(on)/tr/td(off)/tf are 75/36/420/25 ns), so I was hoping they'd be usable, as I have these bricks on hand (plus a number of other slower ones), but nothing smaller! They'll be run with a laminated low-inductance bus design, either with just some aerovox snubbers accross it if I use a supply modulated design, or also with some of the nice RIFA caps if I go for a phase-shift or similar technique. Any opinions on whether they're likely to work? Ideally I'd be able to hit 350kHz or so to give some leeway in the QCW resonator design.
As a background, I've just built a 6.5" DRSSTC as my first coil, but have been interested in the field for a while and work as an electrical engineer. Said first coil seems to work suprisingly well for a first go, though I'm limited to only about a ~1m streamer currently as my MMC is a junk-box creation of 6 different types of scavenged polyprop capacitors (proper caps are in the post). Many thanks go to Steve and Eric for the UD2.5 - while I made a few mods to my version and will make something more original in the future, the design was a great way to get the coil going quickly and (so-far) reliably, and it literally worked first try!
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Well I finally finished the board, time for testing! After I validate this new design I will go into full production and start mass producing the boards, but for now here is what the finished product looks like.
Also just an interesting photo, evolution of the Universal Driver. I'm only missing the mark1 !
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Well that's how I had it on the Rev A however, there is no need for a sink on the 24V reg and a simple small heatsink on the 9V and 5V works just fine. If you did a single heatsink it would have to be custom (ie more work and more expensive) the way I have it set up now it uses $0.7 off the shelf parts that need no more than 30 seconds to install.
Also I have not taken down the Rev A files so if someone likes the all in a line configuration better they can still build it.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
If it is of interest to those making their own UD drivers, the following is the UVLO (undervoltage lockout/trip) circuit I added to my modified UD 2.5 board:
This circuit disables the UD driver when the 24V power supply rail begins to drop. Much better to have the IGBT gates turned off if you lose driver power than to have them end up in a half-on state (or both on if the logic goes crazy at low voltages).
The LM8365 was chosen because I had some lying around at work, it's much smaller than a SOIC so its probably a good idea to look for a larger equivalent if you don't like soldering small SMD parts. There are _lots_ of options out there, check out digikey under ICs - PMIC - Supervisors (make sure you find a open drain/collector, active low part).
As for the circuit: - The two resistors divide down the 24V rail so that the 2.7V UVLO threshold is hit at ~22V (giving some margin for component tolerance). This particular UVLO chip draws very little current, so dividing down it's supply this way is fine unless the resistors are really large in value. - The 1n capacitor might not be necessary, but I put it there for noise immunity and it's time constant is short enough not to compromise the undervoltage trip operation. - The 1u capacitor ensures the undervoltage trip is active for a minimum of ~1 second when it is hit, ensuring everything has a chance to settle down before the output is re-enabled (if the voltage recovers to 24V). Again, this is not strictly required, so the circuit can be reduced to just 3 parts if wanted. - The output of the UVLO chip is a 5V-tolerant open-drain pulldown, so can simply be connected in parallel with the open-collector output of the LM311 OCD trip, giving the UVLO the same effect as an overcurrent trip. - The 12 or 9V (and thus 5V also) regulator should be run off the 24V rail so that the UVLO will function regardless of how different voltage rails are loaded. This will also reduce the chance of over-voltage blowing up the 12/9V reg.
I've done a quick test of the circuit with a variable bench supply, seems to work well.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
Space wouldn't be an issue if you stayed with that particular part (it's tiny) and ditched the capacitors, but some might not enjoy the soldering required.
Couple more notes about it: - The OCD LED will be active when the power is switched on (as the rail is undervoltage during driver power-up). This is probably actually a good thing, and will go out as normal on a fresh interrupter pulse. - 2.7V threshold is probably not the best choice, if you grab something closer to 5V or so then component tolerances have less effect on the threshold voltage. I had the 2.7V parts on hand though.
Space wouldn't be an issue if you stayed with that particular part (it's tiny) and ditched the capacitors, but some might not enjoy the soldering required.
Couple more notes about it: - The OCD LED will be active when the power is switched on (as the rail is undervoltage during driver power-up). This is probably actually a good thing, and will go out as normal on a fresh interrupter pulse. - 2.7V threshold is probably not the best choice, if you grab something closer to 5V or so then component tolerances have less effect on the threshold voltage. I had the 2.7V parts on hand though.
I have soldered some tri-state buffers that have come in SOT23-5 before and they are not too hard with a good iron. If you can get access to a stereo zoom microscope then you will have no trouble.
They do make a 4.5v version of it according to the datasheet and are also available in 2% tolerance (LM8365 AALMF45)
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
OK guys the first batch of fully assembled boards is tested and ready to ship. Here are some photos.
Complete functionality testing, OCD, feedback, fiber, LEDs, etc.
All the boards are marked with serial numbers and time of testing pass data. If you do buy a board form me I expect that you know how to use a UD, I only say this because I don't have time to be answering like "how do I tune the phase lead?".
5 have already been sold or are reserved. I will operate on a first come first serve basis for the rest.
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Universal DRSSTC Driver V2.5 (Sold Out)
