DIY Metcal 13.56 MHz RF Supply

[SeanB]

Here a part of the application process is a reading test, because you find many with a school certificate who cannot do more than read and write their own name.......... And this after 12 years of school.

[mamalala]

Here a part of the application process is a reading test, because you find many with a school certificate who cannot do more than read and write their own name.......... And this after 12 years of school.

Well, he surely can read and write. After all, he was able to read my neighbors name from their mailbox, and write it onto the notification. He just didn't give a damn about his job in general, it seems. He could have said he was in a hurry and didn't check all the mailboxes. Or that he thought the recipient name on the parcel was wrong (my neighbors name and mine share a few letters). But instead he chose to flat out lie into my face, which is just stupid. My name is on the houses front door in big, printed letters. On my mailbox, again in big, printed letters. And on my entry door, dare i say it: in big printed letters.

Ahh, whatever. He surely got his share of abuse from me today. Now back to soldering a pair of these boards, to get things rolling here Already prepared some graphics for the documentation of this thing, now need to figure out a few final part values.

Greetings,

Chris

[cwalex]

Small update: The PCB's arrived today, after the delivery guy messed it up yesterday. First he claimed my name was nowhere to be found. Then wrote a notice for the delivery attempt using a different name (from a neighbour) and put it in her mailbox. Also claimed my name was nowhere on any of the mailboxes here. DHL Express, my ass ;(

Greetings,

Chris

Nice looking boards  Are you going to sell some?

[mamalala]

Nice looking boards  Are you going to sell some?

Thanks!

Sure, once i checked that they work as expected i can hand out the excess boards, no problem. The ten sets came out at around 100 Euros when i got them. This included shipping and taxes. So a single set would be 10 Euros plus shipping.

So far i have the supply/controller board assembled and it works OK, and so does the dc/dc converter part of the generator board. Today i'm assembling the remainder of the generator board, step-by-step, and check it. After that i plan to write up some docu for it, and work on the firmware for the controller board. Then, finally, updating the Eagle files, and packaging it all up to upload it here.

Greetings,

Chris

[mamalala]

Hi all,

that thing works

Today i assembled a complete unit, step by step, testing functionality after each step. Attached are some pictures of the unit, without enclosure.

After i was finished it did not output enough power. I was searching, comparing to the old prototype, etc. After about an hour and a half it dawned me: heck, i now use the 13.56 MHz instead of the 11 of the old unit. Of course! The toroids didn't fit anymore. So i had to sit down and wind a collection of toroids with decreasing numbers of turns, until i found a combination that pretty much matched the old one in terms of output power. Sure, it's probably not perfect yet, but so far it's OK.

In the pictures you can see the main RF generator board mounted flat on a heatsink. The one i used is pretty thick, 40mm. In the end, a 25mm heatsink will do fine. That big thing just gets hand-warm after over an hour...

On top of the generator board is the supply/controller board. This one just generates the +5V and +12V rails, and has a µC for all the bells and whistles. However, it is pretty much optional. Any other design will do as well. The bare minimum is to provide the two voltages and connecting the tip-detection output via a 1k pull-up to the enable line of the generator.

From that it follows that on the main generator board the parts for the SWR bridge can be omitted as well, if that feature is not wanted.

The unit _can_ run from 24 volts supply just fine, however, a bit more is recommended if one wants a really fast heat-up time after power-up. Something around 26 to 28 volts should be OK.

On the current controller/supply boards the buck regulators for the 5/12 volt rails are heavily oversized. That's simply because i used what i had at hand. I have not checked the actual current requirements for these rails, but i think something in the region of a few hundred mA each should do fine. Maybe a bit more for the 12V rail, peak current to drive the FET final is around 1A, but only for a short spike, so some hundred mA plus the buffer cap on the RF board should do just fine.

So, what can it do? Well, of course it happily drives Metcal handpieces/cartridges for the 13.56 MHz system. Oh, and the Thermaltronics stuff for the same frequency as well, of course. The tip-detection works without shutting and locking the whole unit down, like the original Metcal stuff, and thus does not require a power-cycle. Simple pull out the tip and put a new one in, done.

Then i implemented the idea from mikeselectricstuff to allow some form of current limiting. This is done by providing a connection (through a series resistor) to the RF generators buck regulator. Feeding in a positive voltage will decrease the maximum output voltage of that buck, how much depends on the voltage fed into it. Accordingly, feeding a voltage that is lower than what is "normal" will result in boosting the output. The µC can control that with a tri-state pin: pin as input = normal operation, pin as output high = limiting, pin as output low = boosting. I provided two trimpots on the controller board to set both of these option separately.

This is quite a useful option. For example, the limiting option can be used in cases were the power supply/transformer can not supply enough amperes to satisfy the maximum demand during power-up/after tip change. Once the tip reached a certain temp (well, in reality if the SWR reached a certain value) it can switch to normal mode, to still get a good thermal recovery.

But then it can be used to implement some smart standby function. After a while of idling, detected through the lack of bigger SWR changes, the unit can limit the power to send it into standby. This means that the tip does not cool down completely. Once a big downward change in SWR is detected it means that the tip is used. Then it can go into boost mode for a really quick heat-up, and once it reached a certain SWR fall back into normal mode. it then will stay in normal mode until some user-definable timespan has elapsed, after which the whole thing starts over...

Alright, that's it for now. Tomorrow i will work on the documentation, so that i can finally upload the first part (that is, the RF generator board) here. After that follows some doc about my current supply/controller board (plus schema/layout of course). Once i'm done with those two things i will work on a first usable version of the firmware.

Greetings,

Chris

[mamalala]

And here are some scope images of the waveforms with a 50 ohms dummy load connected to the output. One is the output at the IRF510 drain, the next is the output of the RF transformer and the last is the output at the dummy load itself. Output voltage of the buck converter on the generator board is about 21 volts.

Greetings,

Chris

Edit: Keep in mind that i have a really shitty probe, one of these 10 Euro crappy things. Plus, my scope is half-broken (that is, channel 1 is dead, so i don't really know how good channel 2 (which i use) still is....)

[Fsck]

Awesome project! Always looking forward to the updates and definitely jumping on one of those boards!

[peter.mitchell]

Damn, this is looking good, i'm going to start looking at enclosures Speaking of, can you extend the leads on the main FET so it can be mounted on a heatsink elsewhere? Or will the extra inductance mess with the switching?
Also, you say it can run from 24v, but you suggest 26-28v, do you have a definitive voltage and current spec or is this coming?

Sorry about all the questions I'll keep an eye out for the documentation

[SeanB]

That FET is running at 13MHz, so extending the leads is a no no.

[mikeselectricstuff]

Something I was considering is making something for field use to run off a laptop PSU (typically 19V), so you'd only have to take one PSU with you.
This would probably need a buck/boost topology, or a pre-boost stage, complicating things....

[mamalala]

Awesome project! Always looking forward to the updates and definitely jumping on one of those boards!

Thanks!

Damn, this is looking good, i'm going to start looking at enclosures Speaking of, can you extend the leads on the main FET so it can be mounted on a heatsink elsewhere? Or will the extra inductance mess with the switching?
Also, you say it can run from 24v, but you suggest 26-28v, do you have a definitive voltage and current spec or is this coming?

Sorry about all the questions I'll keep an eye out for the documentation

No, placing the FET elsewhere and extending its connections will very likely not work. As SeanB said, this is running at 13.56 MHz. RF is nasty with these things

The 100mm x 100mm x 25mm heatsink is not that expensive and serves as a base to mount all the stuff on.

Regarding the specs for power consumption at different voltages, well, i have to check out those details later. Obviously it will draw a bit more current at 24 volts when idle, since we have buck converters here.

Something I was considering is making something for field use to run off a laptop PSU (typically 19V), so you'd only have to take one PSU with you.
This would probably need a buck/boost topology, or a pre-boost stage, complicating things....

These universal laptop supplies which have a switch to select the voltage can usually go up to 24 volts. And it should be rather easy to hack them to produce 26 volts, if needed, i think.

Greetings,

Chris

[peter.mitchell]

That FET is running at 13MHz, so extending the leads is a no no.

Yeah, i doubted it would, but worth asking anyways, the reason I asked was so I could think of enclosures and heat sink designs for minimal space, 10x10x2.5 is pretty large and heavy for a portable device, If I cut the size and weight down with a smaller heat sink and a fan you could easily offset the extra power consumption with more batteries or a tiny bit larger power supply... Hmm... Maybe I could get a notebook heat sink, add a little fan, bend the heatpipe a little... hmmm... i'd be very much interested in buying/building up one of these, anyway, don't take this the wrong way, i'm like a little kid thinking of things he will do with his birthday presents before he gets them, hopefully you understand.

I made up a few LiPo LVCO boards a little while back, i've been using them for a small industrial PC running of RC LiPos, I think they might come in useful for this too.

[SeanB]

You could get by with a thinner heatsink, or use a laptop heatpipe and make it thin but longer so the fan is next to the board. The power device is near enough to an end to fit one.

[mamalala]

Yea, but note that the PCB itself is already 91mm x 91mm in size. So the only thing that could really minimized is the depth. There are really flat heatsinks available, i think 10mm or so, but dunno how much they cost.

Also, you could probably use the base/wall of whatever metal/alu enclosure you chose and mount the PCB flat on there, and add a fan on the outside. You can also place the FET upright instead, and figure out some other way of attaching a heatsink then.

Another issue to consider is the buck regulator and the FET driver on that board. I placed a bunch of thermal vias underneath each of them. The buck itself already has a thermal pad, which i solder as well. On the bottom side of the board there is no solderstop in that area. So in my setup i put a dab of thermal compound there as well.

No idea how hot the buck would really get, and for the driver it's more of a "better safe than sorry" thing. Maybe its already enough the way it is due to the copper groundplane, or maybe glue some small heatsinks on top of those parts as well. Time will tell...

Greetings,

Chris

[mamalala]

Something I was considering is making something for field use to run off a laptop PSU (typically 19V), so you'd only have to take one PSU with you.
This would probably need a buck/boost topology, or a pre-boost stage, complicating things....

It just occurred to me that maybe it is possible to wind the RF transformer a bit differently. Right now it uses a bifilar winding, that is basically two windings with the same number of turns. Maybe the output winding could get a few more turns to transform it up a bit more, thus making up for a lower supply voltage.

Greetings,

Chris

[mikeselectricstuff]

Something I was considering is making something for field use to run off a laptop PSU (typically 19V), so you'd only have to take one PSU with you.
This would probably need a buck/boost topology, or a pre-boost stage, complicating things....

It just occurred to me that maybe it is possible to wind the RF transformer a bit differently. Right now it uses a bifilar winding, that is basically two windings with the same number of turns. Maybe the output winding could get a few more turns to transform it up a bit more, thus making up for a lower supply voltage.

Greetings,

Chris

I was wondering that but assumed that higher current in the MOSFET may be a problem. 

    Something I was considering is making something for field use to run off a laptop PSU (typically 19V), so you'd only have to take one PSU with you.
    This would probably need a buck/boost topology, or a pre-boost stage, complicating things....

These universal laptop supplies which have a switch to select the voltage can usually go up to 24 volts. And it should be rather easy to hack them to produce 26 volts, if needed, i think.

I was thinking more along the lines of making it work with the laptop PSU that's probably already going to be in my bag, so would need to match that.  Running off a laptop or power drill battery would also be a nice option, but that would certainly need some boost.   

[SeanB]

I would guess there is plenty of current drive spare on the mosfet, or you can just use a higher current one in the same family.

[mamalala]

Alright, here is the docu of the main RF board.

Here it is attached as the original Libre-Office .odt file. In the next post i attach it as PDF file.

The .odt is very basic, plus lots of images/graphics. I'm too stupid with that office stuff to add a proper index, etc. If anyone can and wants to help out, this original file should be useful for that purpose.

Greetings,

Chris

[mamalala]

As said, here comes the same but as PDF, for those who don't have Libre-Office installed or otherwise can not read the .odt files properly.

In the next post i attach the Eagle files and a PDF of the current schematic.

Greetings,

Chris

[mamalala]

And here are Eagle files in the ZIP archive, as well as a PDF of the schematic. Silly Forum software doesn't allow for .sch and .brd files, so i had to pack them.

Please note that i still use Eagle 4.16. So if you make any changes that you want me to include in this project, make sure that i can read your files. That is, if you edit it with never version i'm out of luck. In that way i would have to manually add the changes to my files...

The (c) of these files and the docu is with me, of course, but you are free to use that stuff as you see fit. The only request i have is that if you base your own design on this and distribute it, that you properly mention that the original design is (c) by me. And of course i can't stop (nor will) stop you from commercializing this thing. However, it would be nice if you would contact me first in that case.

Once the new-years frenzy is over i will do the same for the supply/controller board i made.

Have fun, and greetings,

Chris

[mikeselectricstuff]

Thinking about it, it should be pretty easy to use a boost reg instead of the buck for operation at lower voltages. What's the  lowest regulator output voltage when idling?

Also, any chance you could measure the power draw from the 5V and 12V rails?

Is there any need for the fwd/reverse power measurement part other than debugging? What's the reason for it being the length it is?

 

[mamalala]

Just noticed that i forgot to change one part value, and thus have it wrongly in the schematic and description. R23 (around the OpAmp) should be 22k instead of 2k2. Have updated my files here, but won't upload them again just for this small change. Just make some notes about it

Once everything is published and folks have played around with it for a while (and maybe found some other bugs/errors) i can then upload a new set with all the corrections included.

Greetings,

Chris

[mamalala]

Thinking about it, it should be pretty easy to use a boost reg instead of the buck for operation at lower voltages. What's the  lowest regulator output voltage when idling?

Also, any chance you could measure the power draw from the 5V and 12V rails?

Is there any need for the fwd/reverse power measurement part other than debugging? What's the reason for it being the length it is?

Hi Mike,

yes, using a boost regulator should work as well, i think. The lowest output voltage depends on how one wants to fine-tune the thing later on. The values i have given in the docu are just pointers to get something working. My unit here is happy with 18-19 volts idling, going up to over 22 volts during heat-up.

The SWR bridge is purely optional. It's nothing more than a piece of the "bells and whistles" stuff i added. So you can remove it if you want to redesign the board. The length has no special meaning. It just happens that this layout and length is something i used earlier in other circuits and found to work well enough. It can't be too short, otherwise it will produce too little voltages, and the differentiation between forward and reflected isn't that goo either, i think.

So you could use that space to put the 5/12 volt supplies there. As for the 12 volts, it surely is only a few mA since it has only very few components attached to it. For the 12V rail i'm not sure, some hundred mA definitely. I will do some measurements after new-years frenzy. Reminds me that i still have to replace the fuse in my shitty multimeter....

Greetings,

Chris

Edit: Of course the SWR bridge is usefull to detect gross mismatches due to whatever reason. under normal conditions the SWR goes not above 8 or so, depending on the used tip.

[mamalala]

Oh, and the idle voltage also depends on the tip. Larger tips will have a higher idle voltage since they loose heat due to radiation and their larger surface area.

Greetings,

Chris

[mikeselectricstuff]

Just been looking for some UK sources for magnetics. Turns out Amidon are just distributors for small qtys of cores from Micrometals and Fair-rite

RS stock the FT82-61 , Fair-rite p/no 5961000601  http://uk.rs-online.com/web/p/ferrite-rings/4674267
Farnell also list it, but as US stock:  http://uk.farnell.com/fair-rite/5961000601/ferrite-core-toroid-61/dp/1781353?Ntt=5961000601

Pace Magnetics stock the T80-6 and T50-6 (£3.95 UK postage)


RS are also cheaper than Farnel for the ISL55110, but sold in packs of 2