DIY Metcal 13.56 MHz RF Supply

[mamalala]

Chris,

Why are the 10 ohms resistors there at all? You have a driver that has a rise fill time under 2nS and 3.5A capacity, and that is great. But then you slow it down with the 10 ohm resistors. I do not get it. I understand putting 10 ohms gate resistors in a linear circuit to prevent oscillations, but in this case, the only purpose is to make the mosfet switch slower and get hotter. Are you slowing down the mosfet so it acts as the snubber for the transformer?

When i tried using only one driver channel and no resistor, which is what i did in the very first test circuit, i pretty much always ended up with a dead driver after while: it simply got way too hot. After all, this is only a very small chip with no thermal pad to act as a heatsink.

Plus, it still does not explain how the buck's output voltage can rise all by itself once a certain load is reached, i.e. from 15V to 20V and probably beyond.

Sure, it may have been the rather poor quality layout that i had in the very first circuit that caused the driver to fail after a while always. There is no problem using different/no resistors to check that out in the current one. As i have repeatedly said, i'm no expert in RF circuits anyways, so there surely is lots of room for improvement there. All i can say for sure is that it works just fine for me, in more than one of these supplies that i built, with at least two different brands of the IRF510, and under more "extreme" conditions. I can only go by what i have working, and only compare to what i have working, after all.

Greetings,

Chris

[gnif]

All those that were trying to read/respond to page 12 of this thread, it is working again. It seems that the last post by mamalala was the cause of the issue, not sure as to what it was, but by pruning it from the database and manually re-inserting it, the issue was resolved.

[amspire]

I was wondering why I was getting a blank page. Thanks for fixing it. 

[mamalala]

Many thanks from me to gnif as well for looking into (and fixing) the issue. Great job!

Greetings,

Chris

[Paulinho19]

Great, we are back. 

What's new, My RF-Borad is finely working, the problem seem to be the XFMR, chris send me one of his and all problems went away. He only explanation that I can find is that RS send me the wrong ones. I will test them both next week with a network analyser to see what's the diference. I will also test a few Metcal tips.

Meanwhile I finished my controller board design placed an order at iTead, my board are already on there way to Portugal.

Paulo

[Paulinho19]

My Board.

[EEVblog]

PLEASE READ
There is something wrong with this thread in SMF, it is giving technical troubles. No idea why. 
Thread locked unless a fix can be found.

Dave.

[gnif]

Unlocked and fixed, problem was the large image upload. We will have to see if we can impose an image size limit on uploads, people need to be a little less lazy and prepare their images for the web.

[Paulinho19]

My fault 

In fact the image is very large, I must have done something wrong, but still it is less than half the maximum size allowed (2000kb)

Anyway I will be more careful with that,

Thanks and ones again sorry for all the trouble,

Paulo

[mamalala]

Hi all,

a few notes and status updates here.

First of all, i noticed somethig weird regarding the power output. Either the supply voltage radings found in the MX500 document are wrong, or my circuit is way more efficient/better-tuned. If i set the idle voltage to around 18 volts, i get some of the tips glowing dark-red around where the coil is! That means way too much power is pumped into the cartridge for too long. Setting the idle voltage to around 12.5 to 13.5 volts, which is way lower than what can be found in the document, makes everything work nice again. Of course this value is for small/medium sized tips. Larger tips idle at a slightly higher voltage (13.5 to 14.5 volts).

Anyways, during heatup (or boosted power at wakeup) a supply of around 21.5 volts goves a nice, fast heatup time.

I also made slight modifications to some part values. The reason is that i am currently very busy working on the firmware, and thus found out a few things. Here are the changes:

- On the RF board, use a 100 Ohms resistor for R11 (this one involves the µC-controlled power limit/boost function)

- Again on the RF board, change R8/R9 to 4.7 Ohms. Those are the gate resistors of the IRF510.

- Still on the RF board, change R33/R34 to 100 ohms each. This provides a lower impedance of the VCC/2 voltage for the OpAmp in the control-loop.

- The last change on the RF board is to use 22 Kilo-Ohms for R23 and 1 Kilo-Ohm for R24. These are also for the control-loop OpAmp, setting a higher gain.

- On the controller board, the variable resistor to set the boost power should be 1 Kilo-Ohms, that way a nice adjustment is possible. The one for the limited power is 10 Kilo-Ohms.

The maximum supply voltage as given by adjusting R32 on the RF board should be around 21.5 volts (no boost/limit active, purely the control loop). Regarding the idle voltage fo the tips, here is a rough overview for some tips:

Between 12.5 and 13.5 volts_

STTC-147
STTC-126
STTC-037
STTC-025

Between 13.5 and 14.5 volts:

STTC-011
SMTC-147

As for the limited and boosted voltages, it turns out that in limit-mode a voltage of around 10 volts, and in boost mode a voltage of around 18 volts give good results. For example, adjusting with a STTC-147 tip would be done the following way:

- Insert the cold tip. Power up in normal mode and monitor the voltage. Adjust R32 so that it never exceeds 21.5 volts. If it does, let the tip cool down again and repeat this step.

- Once the tip reached temperature, adjust an idle voltage of about 13.5 volts using R19. Let the tip cool down and repeat the previous step. If required repeat these two steps as often as required to rech these values. Should be very easily done, however.

- Let the tip sit idle at normal power, that is, no limit or boost enabled, for about 10 minutes. Re-adjust R19 to give an idle voltage of around 13.3 volts. Let it sit that way for 10 more minutes, and if needed make slight adjustments to R19 to bring it back to 13.3 volts.

- Enable the power-limited mode. This is done by pulling the controlling microcontroller-pin to GND. That pin goes though an 1N4148 diode, then the 1k adjustable resistor, into the VLIM adjustment pin on the RF board, where it ends up at R11. The diode is connected with the cathode to the microcontroller pin and the anode to the adjustable resistor. Now adjust that 1k trimpot to give a supply voltage reading of between 10.0 and 10.2 volts.

- Now enable the power-boosted mode. This uses the same microcontroller pin, but this time pulled high to +5 volts. This signal now goes through another 1N4148 diode, then through the 10k trimpot, and again ends up at the VLIM pin of the RF board. This diode is connected with the anode at the microcontroller pin and the cathode at the adjustable resistor. Now set that 10k trimpot so that you get a supply voltage reading of roundabout 18 volts. When done switch back to normal mode...

This concludes the adjustments required to the circuit, and it should now be fully operational. The unit is now adjusted such that in normal mode the tip is kept hot and that load changes are quickly detectable. In normal mode the control loop will nicely adjust the supply voltage to keep the tip at the temperature. During limit-mode, which is very usefull to implement auto-sleep, any slight load change will cause a huge change in the available readings (forward-voltage, reflected-voltage, and subsequently the calculated SWR and power levels). Even pulling the handle out of the stand causes enough load change to give a huge delta-reading of the above values combined. Also, when waking up, the boost-mode now allows for a quicker recovery if needed.

I will explain how to use those values to detect changes, etc., in the next post later today explaining the firmware that i am working on.

Greetings,

Chris

[mamalala]

Hello all,

here is a somewhat functional preview-version of the firmware that i am working on. It generally works already, but a few things are still missing, most importantly the menu/UI handling and structure. While i already have a menu system ready from other PIC projects, i still have to add it to this one.

Note that this is purely a preview thingy, meant to let you see in what general direction i am going with this. This also means that virtually none of the code is documented yet. Of cpurse it also means that certain things are rather messed up right now (for example the main() loop), and that other things will undergo quite some changes. One example of that is the state-machine logic of the power-manager. As explained in my previous post, i had too high supply voltages in use. That resulted in having to do some things in a rather messy way since i got only very small changes in the readouts (no surprise, since the tip was way too hot). Now that these issues are fixed, some parts of the power-manager stuff will get reworked.

That said, here are some of the main features of the firmware:

- Multi-language support (currently only English and German)

- Extensive logging output through the RS232 port

- Manual control or automatic (power-managed) control

- Up to 8 different setups can be defined and stored in the internal EEPROM. Each setting can be given it's own name up to 16 characters long

- Virtually every aspect of the firmware is configurable with these setups

The used micro is a PIC18F2620 running off the internal oscillator. The project is done using MPLAB-X, the used compiler is microchips C18. The IDE and compiler can be downloaded from the Microchip website free of charge.

The power-management is freely configurable and allows for a variety of power handling. For example, during initial startup the power output can be set to limited, normal or boosted. Exiting the startup phase can be done either by time, actual SWR reading or by monitoring the changes in the readouts and use a threshold for them. After startup it enters a heating/heated phase that monitors changes in the readouts. If those changes are below a given threshold after a given time, it will enter an idle state. It exits that idle state if a given threshold in changes in the readouts is reached and re-enters the heating/heated state.

After some time in the idle state, and with changes in the readouts below the threshold, it can enter a sleep state. In that state the output power is limited. It will wakeup once a defined change in the readouts is reached. If it wakes up, it can wakeup in normal mode or in boost mode, the latter speeding up thermal recovery. The boost-mode wakeup can be either timed, SWR dependant or again depending on a threshold in the readouts. If it stays in sleep, it can enter power-down mode after a given time. In that mode the RF output is turned off completely. In that state, using the rotary encoder/button will restart the power-manager by enetring the initial startup-phase.

Normal operation, sleep and powerdown can be indicated by the LCD's backlight. Indication can be either a fixed backlight level, a contnous fade-in/fade-out cycling of the backling, or by flashing it. The levels and times of these modes are, of course, configurable as well.

Besides these config-sets, there is a single main config that defines in which mode to startup, which language to use and which config-set to use.

One might ask why so many parameters, some of them with little relevance to the overall operation like the backlight stuff, are configurable. Well, because we can, that's why I mean, it's always the same. Not making them runtime-configurable makes some people complain that they need to recompile the code to make changes to them. Making them configurable in turn makes other people complain that there are so many parameters...

In any case, there will be a nice menu-system that allows for easy configuration. Only a rotary encoder with pushbutton-function is then needed to control everything. The UI interaction can be either through the LCD or through the RS232. The latter will then allow for configuration as well. This way the configuration will be portable between units: export them by dumping it through the RS232, import them by feeding back that dumped data into the RS232.

Alright, that's all for now. Back to working on the code...

Greetings,

Chris

[mamalala]

Just a quick note to those who may want to use a laptop power-supply brick to power this circuit. You can use one of these universal supplies that go up to 24 volts, and then modify it slightly. I have such a supply that is switchable between 12/15/16/18/19/20 and 24 volts, the latter two up to 4 amperes. There is a standard voltage divider made of resistors in it for the feedback that, if left alone, produces 12 volts. The additional voltages are selected by simply switching an additional resistor in parallel to an existing one of that divider. Just swapping the resistor for 24 volts to have it produce 26.5 did the trick.

It works just fine with such a supply.

Greetings,

Chris

[mamalala]

Hi all,

while working on some magic-8-ball type of addition to the code (hey, i try to predict the actual tip....), i noticed some quite dramatic differencies between original Metcal cartridges and their Thermaltronics equivalnt. While i have only 3 types of equivalent Thermaltronic tips, the trend is quite visible!

For example the STTC-025 Metcal tip compared to the allegedly equivalent/compatible M6CH178 tip from Thermaltronics. During power up from a cold tip, my firmware reoprts > 99% consumed RF energy (relative to the provded energy) for the Metcal tio, but only around 71% for the Thermaltronics.

NOTE: My power calc algo is somehwat bogus, but still relies on the forwarded RF energy vs. the reflected energy. In any case, hte supply voltage to the RF stage is the same in both cases.

Once the tip reached temp, i get an an idle supply voltage of 13.44 volts for the Metcal, and 14.58 for the Thermaltronics. The reported power consumption is 14.1% for the Metcal vs. 33.4 for the Thermaltronics.

More interresting is the reported change to thermal responses. Wiping the idling tip over a damp spnge gives me a delta of 23 for the Metcal, vs. a delta of 15 for the Thermaltronics. Similarily, wiping the tip over one of these dry brass-wool. thingies for one second gives me a delta of 13 for the Metcal tip, and 7 for the Thermaltronics equivalent.

It might also be noted that the previously "dark red glowing" cartridges were always the Thermaltronics ones (of course not the tip glowing, but around the internal coil assembly....)

Something strange is going on there, considering that the electronics (which includes the controling feedback loop) is always the same. In general, the Metcal tips idle at a lower voltage (even such things as the SMTC-147 which have a huge surface area) compared to the few Thermaltronics tips that i have available...

Greetings,

Chris

[mamalala]

Cool! I've always wanted a small lightweight Metcal supply for on-site use - SMPSU for light weight and fan cooled to minimise heatsink. Maybe even a battery option...
Do you really need the MCU?

Comming back to this post, i have to say that no cooling fan is needed.

I use a SK92/100 heatsink from Fischer. During normal operation it feels "cold" to the toch. Onyl after using a big tip for quite while (to solder a 2 cent coint to a copper.clad PCB, for so long that i can freely move the coin in the solder blob molten around it), it gets hotter.

So, i would say that for nomral operation no extra colling besides a heastsing is needed. I think that even a SK508 or SK505 should be well enouhg. (the 505 is 15mm in height, 508 is 25mm and the 92 that i use is 40mm, all of them with 100mm * 100mm length/width)

Greetings,

Chris

[Tioleco]

This circuit work with Thermaltronics handle and cartridges of this ebay seller?
http://search.ebay.com/?sass=denbo32&ht=-1

[mikeselectricstuff]

This circuit work with Thermaltronics handle and cartridges of this ebay seller?
http://search.ebay.com/?sass=denbo32&ht=-1

Yes - but only the handles with the F connector (MX series) and STTC or SMTC tips.
The ones with the DIN connectors are for the 470KHz systems.

[mamalala]

Hi all,

just a little time to continue working on the firmware, and added some logging functionality that allows me to plot certain paramaters using Gnuplot.

So, i sat down and logged all the tips that i have, each one for 2 minutes. These plots show the heatup phases for them, after heatup they just idle in the stand. The first 6 are Metcal tips, the last three are Thermaltronics tips. I uploaded the images to an external image hoster, since one of them is really large. Just click on the thumbnails...

The Y scale is in volts for the supply voltage and the VSWR, the X scale is in seconds. The values for forward, reflected are the raw voltage readings from the SWR circuit multiplied by 10.

STTC-147

STTC-126

STTC-037

STTC-025

STTC-011

SMTC-147

M7DS525

M6CS155

M6CH178

I also made a longer plot while using the STTC-126 tip. Be aware, this one is about 7k pixels wide. It shows the following events at roundabout the times given:

(Edit: The sleep mode reduces the supply voltage, and when waking up, it goes into boost mode for a few seconds and then switches back to normal mode)

16 seconds - heated up
142 seconds - entering sleep mode
239 seconds - wakeup by quick swipe on damp sponge
300 seconds - quick swipe on damp sponge, soldering pads for DIP package
420 seconds - quick push into brass sponge
450 seconds - soldering copper clad pcb, bare and unetched (=massive copper plane)
594 seconds - entering sleep
719 seconds - wakeup, quick push into brass sponge

There is an additional trace in this plot in cyan. This one shows the total delta of the monitored parameters, this determines the idle state, sleep state, wakeup, etc.

STTC-126 while in use

Greetings,

Chris

[zoltan]

Hi,

First, I have to thank Chris for his work. It's a great contribution to electronic hobbyst community.

Now, here is my question. Farnell doesn't have the smps chip anymore. But I've already sent the gerbers to Itead and boards are in production right now.
Can I use the lm2673 version instead of lm22676? I suppose that pin 5 should be lifted and connected trough resistor to the ground, but I'm not sure that's enough.
Update: Found that LM22670 is available. Canceled the boards production and sent them the new design. Thank everyone for help.

[Paulinho19]

Hi Zoltan,

you can register at Texas Instruments an order up to 3 samples of the lm22676 for free and it is delivered in less than 48h.

Or you can buy them at RS or DIGIKEY, they still have them.

Paulo

[mamalala]

Hi,

First, I have to thank Chris for his work. It's a great contribution to electronic hobbyst community.

Thanks!

Now, here is my question. Farnell doesn't have the smps chip anymore. But I've already sent the gerbers to Itead and boards are in production right now.

Hmm, for me, Farnell does list it as 1009 pcs. available. The correct part number is LM22676TJ-ADJ instead of the LM22676TJ7A that i placed in the schematic. That issue was mentioned by Mike quite a while ago (that is, that the labelling was wrong in the schematic).

Can I use the lm2673 version instead of lm22676? I suppose that pin 5 should be lifted and connected trough resistor to the ground, but I'm not sure that's enough.

Not really, it's too different. The LM2673 needs parts for a softstart and current limiting, which are not there, and it lacks the EN pin to enable/disable the chip by the µC.

Greetings,

Chris

[zoltan]

Hi all,

Paulo, no chance I'll order samples any more - it cost me to much - minimum 50eur customs even for free sample. Because it's sent by FedEx only, and local FedEx is forcing everything trough customs. RS is expensive as hell here, almost 10eur/pc (i need 3)  but if i cant get it any other way that would be the solution.

Chris, part number is  1657733. That exact number I put in my order list to local Farnell distributor and they say delivery time >4 months. Now, I've checked on german Farnel and it's there, 1009 pcs of 1657733. Strange. I'll call my distributor and tell them this.

The LM2673 current sensing part is actually not so problematic. You just need to lift the pin 5 and solder a small 0805 resistor between pin and GND. I'm not sure about cap on the softstart pin. Does it allow shutdown or not.

[zoltan]

I've just received a response from my local distributor. They say that "our" warehouse is in Leeds and their stock is the only relevant for us. Sad.
Anyone is willing to order from germany and resend to Croatia? I'll pay in advance (paypal).

[mamalala]

I've just received a response from my local distributor. They say that "our" warehouse is in Leeds and their stock is the only relevant for us. Sad.
Anyone is willing to order from germany and resend to Croatia? I'll pay in advance (paypal).

That's strange, since the UK Farnell site also lists it as 1009 available as EU stock, so i'm not really sure what the problem is. Guess your local distributor is just messing around with you. Who knows, maybe he's not interrested in small orders...

Just sent you a PM regarding the chips. But i'm wondering how you come up with a50 Euros for customs on free samples. After all, they are declared with no commercial value, usually. Plus, how is sending you stuff going to work then? If they want customs in one case (free samples), do they not want customs in the other case (if i would send them to you) as well?

And heck, even if they want customs for free samples, i still wonder how it comes to be 50 Euros. That is a multiple of what, lets say, 3 of these chips even cost.

Greetings,

Chris

[zoltan]

Offtopic

I'm supposed to check availability on Export site, and there is zero of them available (but it's not restricted item).  This distributor will sell you anything, you can order a single 0805 resistor and they will deliver it, except they will add 15 € fee for orders below 50 €. It's even cheaper than the deutsche site, eg. the 1657733 costs 4.92€+VAT and here costs 4.27€+VAT. But it's not available.

Re the 50€ for customs charge. The problem is only with courier post (FedEx, DHL, UPS). The have they own customs warehouses with they own customs officers employed inside so they force every single parcel trough customs. Even if customs end with zero amount to pay, you are charged with "handling and storage"  fees (payable to courier) that differ from one tho another (FedEx ~50€, DHL ~30€, UPS ~30€). Ordinary post (registered, EMS) is something different. Sometimes the package get caught by customs (most often not) and I have to pay that. But much less and more transparent (10% for most things, 0% for electronics, +25% VAT for everything). In Croatia most people use couriers only once for international. After a hard lesson they use EMS 

I hope things will change fast after we enter EU.

Back to the topic:

I'm right now checking for replacement parts that are available on export and it seems that the best candidate is LM22670-ADJ. It has Sync functionality on pin5, but it can be left floating. Other than that, other functionality is the same. I'll check it one more time when I get home from work, but I'm almost sure it would work.

Btw, thanks for your offer, Chris.

 

[mamalala]

Offtopic
Re the 50€ for customs charge. The problem is only with courier post (FedEx, DHL, UPS). The have they own customs warehouses with they own customs officers employed inside so they force every single parcel trough customs. Even if customs end with zero amount to pay, you are charged with "handling and storage"  fees (payable to courier) that differ from one tho another (FedEx ~50€, DHL ~30€, UPS ~30€). Ordinary post (registered, EMS) is something different. Sometimes the package get caught by customs (most often not) and I have to pay that. But much less and more transparent (10% for most things, 0% for electronics, +25% VAT for everything). In Croatia most people use couriers only once for international. After a hard lesson they use EMS 

Funny, here in Germany it is the exact opposite. DHL charges no handling or whatever fees (OK, they are a Germany company and have special privileges regarding customs: They are the only ones allowed to do it themselves). Never had to pay anthing to FedEx either. Only UPS tried that once with me, and i simply refused to pay it but got the package anyways. All that for handling/storage fees, of course regular customs and VAT still applies (but never for samples either).

However, EMS is really bad here. They don't deliver themsleves, but use a subcontractor here in Germany, and they are the worst you can have. While they theoretically allow you to do the customs clearance stuff etc. yourself, they delay the notifications until it is almost too late, basically forcing you to pay them hefty sums of money. In Germany, you better avoid anything that uses EMS for packages.

Greetings,

Chris