Just use aluminium pcbs and forget about this problems.
Do you have a source for cheap Aluminum PCB fabrication similar to OSH Park’s service? It would need to be available worldwide, easy to use, and very reasonably priced for small lots.
Yes. (If it is available in Russia, it is 100% available in EU and US).
OSH is just user-friendly service for beginners. Thousands of US based companies can do same work.
As you can see from all this $1 10-15W led plate lights from china, this technology is very low-cost nowadays. Regular alibaba seller can supply alu pcbs from 100sq.m for $40-50/sq.m. This is almost zero for 17mm board, even if youll order just one square meter sample board and will pay several times more for small order.
Well, if “OSH is just user-friendly service for beginners” then that’s still what I’m looking for, but with aluminum (and copper?) PCB’s for a very reasonable price @ small quantity (sample size 3-5 pieces). Oh yeah, OSH Park also provides ‘free’ shipping world wide (included in price). Can you provide us a link to a place like that?
Edit: I know there are plenty of fab shops that can do inexpensive work @ medium or large quantity. I’m specifically looking for a cheap price @ small quantity, including free shipping worldwide. That’s what OSH Park provides that makes them so attractive to BLFers. I basically want exactly OSH Park, but with metal PCB’s.
Actually the opamp does the trick here. It has a pretty firm hand on the FET. The limitation we do have is the granularity of the 8-bit ‘DAC’. With the driver set up for 3 A, for example, we can only control in steps of 3/255 = 12 mA. But even that first 12 mA is rock-stable.
There is the small issue of opamp offset, which boils down to that first 12 mA step actually being slightly lower or higher, depending on the specific sample of the opamp chip. The two opamps selected are ‘low-offset+zero-drift’ type, so this error is very small, typically < 0.2 mA in the 3 A example. This error is also stable for the particular sample of opamp.
Basic operation is the MCU creates a reference voltage (the ‘DAC’ signal) for the opamp. The opamp amplifies the error between this signal and the voltage over the big current sense resistor. It then drives the FET to where this error is zero.
The ‘DAC’ btw, is just a heavy 1st order RC filter on a PWMed output from the MCU. It works (surprisingly) well and since the opamp is heavily over-compensated does not need to be perfect DC either.
As TA mentioned, there is an optional moon channel to get below 12 mA. It drives the emitter directly from an MCU pin through a large resistor. Moon current can be selected by changing the resistor size or by PWMing the channel. This channel is not regulated of course, so the PWM option might be interesting (firmware regulation based on cell voltage).
And oh, great to have you back TK! I like where the ‘optic nerve’ stuff is going. (You might want to try adding a 20-100k resistor from LED- to BAT+ to get a better signal, or even try with the MCU internal pull-up enabled.)
Yes, that DAC looks familiar ;). Ti has a nice writeup of a similar thing:
but this version of it looks a bit more familiar:
https://budgetlightforum.com/t/-/42480
The picture in post 5 is a lot like Ti's but the OP is a bit of a different thing, and is the thing here. The difference (for the 1-stage versions) is if you apply a pulldown resistor (R4) to help achieve the desired voltage, the importance being that doing so improves ripple.
This is not real due technical abilities. For 3-5pcs you can buy alu-based blank and make them by your own.
OSH Park are making their work great. But they have three type of boards, one type of mask, one type of copper finish and thats all. Prices per sq inch are not cheap ($3.15 for three led switch boards, you can order full assembled lightening switches from ali little cents more). I can suppose that OSH Park have different process with small size blanks and this way they can keep cliche for all steps.
More usual way, is using big size blanks. There is almost no way to find them in Cu. With this way all steps and all machines are made just for this size, there is no way to bring smaller size piece and ask to make your pcb, anyway it will be made from full size blank. Thats why minimum reasonable order can not be less than 0.5 or 1.0 sq. m.
One more problem with metall core pcbs, is milling. Square boards can be cutted other way, but round ones require milling with complete different tools and rates from those that can be used with glass fiber boards.
P.S. Most alu-based blanks are one-side, this can be problem. From the other side, soldering one-side driver on aluminium board can be fast and repietable in medium quantities.
kiriba ru that's the point though. Most people just want a few (three or even less), and yes $3 a board is probably outrageously expensive per area, but no compared to your option of doing building them yourself, a few bucks when all you need is a few small boards anyway, isn't a big deal. There's no better option really. You want to spend hours making a $3 part? Well ok, I guess that's somewhat what folks do around here, but well, there might be some limits. Group buys could work, but really I don't think that fills the needs. If you could get RMM in, that would help, but doesn't solve international shipping.
OSH Park uses full size blanks. They put multiple orders (from multiple customers) on each blank, until it is full. That way, they can offer small sample sizes. They do have a couple of different choices available, not just one. And the pricing starts at $5.00USD per square inch for three copies (so really $1.67/in² ) shipped worldwide. It isn’t the cheapest way to get boards made, but more convenient for small sample size than most other shops.
Esty sells round copper blanks for cheap. Maybe using a blank with kapton tape would work? Might be a mess though
Board is just one small part.
You can share design and smb will be able to order one pcb.
Then he needs to order mcu, diodes, smd resistors (sold in 100 or 1000 packs) and etc.
Then he needs to order mcu clip, cable, adapter for programming.
All this work looks silly, hundreds of blfers are making same drivers by one when smb could make 100.
And yes, if we will look forward to buck and boost drivers, we will see that proper components are made by 2-3 companies in the world, they dont have wide distribution and there is almost no way to get equil component in different countries (I cant make meteor driver copy because parts that can be ordered from Moscow are different from those that are selling in Kyiv).
100's or 1000's? There's exactly one of the drivers in my light, and before I made it, nobody knew if it would work. Sure, then group buys come, designing lights with thorfire. But then people want the dirver from one light in a different light. You can't get custom and mass produced too and there's just not that much market for boards at all to sell more than a couple of designs retail, fully built. Given the price of some expensive lights, I wouldn't say it actually to me thaaat long to construct this either, R&D notwithstanding.
For you own light, you dont need high quality mask or finish. You can use “laser iron” technology (print layout with laser printer and copy this image to the copper layer with old heavy iron).
I suppose you dont understand what are you talking about. With normal technology, second blank adds 20-30% to the price of the first one. This means that 70% is cost of clishes for all steps.
OSH are based on small orders of shared projects. Most buyers are not able to make their own design and just order existing projects. If you will fill big blank with big amount of different designs, you will need to make new cliches several times a day.
I think he knows what they say they do, and he also know the end result, that is good for us, and that nothing else really competes with for its purpose. I'm not sure what point you're trying to make. Sure we could iron our own. Ok. If you want to make up 100,000 of your favorite boards and start setlling them cheap from a proper online store front, I'm sure people will buy them (not sure 100,000 will). We'd love you.
. I’m assuming you’ve already looked at the QX7136?
A 2nd order filter would be an overkill here. The opamp is heavily over-compensated to ensure stability in any use. A side-effect is that almost no ripple makes it past the opamp.
Also too much math in those links 
. I just kept the RC cut-off frequency two orders of magnitude below the PWM frequency, ~50 Hz IIRC.
That's not a second order filter in that post. It's a first order. It's the same design you have here and the same one I put on the Texas Buck. The only difference being R6, which doesn't seem very exciting. yeah, for that buck, we needed to have the ripple tightly controlled. It turns out a bit more complicated than just RC, becuase you've got a different R for charge and for discharge, and the ripple fraction ends up depending on the actual output level, but yeah, basically of course if you're in the percent ballpark on that estimate, you're not going to end up with 30% ripple of course (except with very low PWM levels).
Besides 20mA more, is there any other advantage with the QX7136?
If this is true, it might explain why OSH Park makes a minimum of three copies of each board design. It makes sense to me. Three blanks, one cliché. But, you’re right. I don’t know what I’m talking about. I only know what they claim on their website. And I don’t even care how they do it. Only that it is convenient for me. That’s why I asked if you have a link to a fab shop that does it exactly the same way as OSH Park, but with metal PCB instead of FR4. That’s really all I want. Everything else is unnecessary argument from you, because I don’t care how any of it actually works.