Most of those resistors are chosen as the cheapest, not the best. You can get lower temperature coefficients for a price. TA says many of the big parts are also maybe cheaper on Mouser. I think that was arrow. Anyway, mouser is actually a few cents more.
Like buying a Corvette and going to Discount tire for the 4 for $99 special when you need tires… Why are those the cheapest resistors? I plan to build this driver, I don’t want the cheapest, I want the best or it isn’t worth the time y’all have spent sorting all this out.
Nah, it's more like getting it with stock tires actually. These are all 100ppm/C which is quite good actually. For 100C delta (so up to 125C absolute) that means 1% change, so at most you're at 2% total off the nominal value then. Yes for 2 resistors that could be read as 4% total, but it's not since the thermal coefficient isn't random, and both heat up the same way.
In fact though having two in every divider means it's almost no effect at all since they both change in the same direction. This won't hurt performance. The worst it will do is mean your max mode 0.5% different than what you think, as if it will really be that close even if we did use 0.1% resistors. Of course you can order what you want, but I think these are actually the most sensible. Anything more is probably like probably like buying gold plated fuses for the AC input to your audio amp.
I suppose I might not have been careful to match brands for dividers. I probably could do that at least. I'll give it a look when I get a chance.
I measured resistance from PBx pins to both VCC and GND on an unconnected MCU. I got varying results but the lowest was in the 4 to 5 mega ohms range. Things are probably different when it’s mounted on a driver.
I didn’t think about the zener case either. In any case I’d guess that a driver with the LDO solution would provide more stable readings than one with the zener solution, or at least differently. The zener does what it does, it’s passive, but the output pin of the LDO probably behaves differently when there is no input voltage.
The off time cap is measured before it gets any voltage. The cap doesn’t get charged until the pin it sits on is set to output high in the firmware, at least this is the normal method in “standard” driver designs if things haven’t changed lately.
Updated cart above. To give an idea how powerful that browser tool I linked is.. it generated this for me from my table above, and populated my shopping carts for all of them:
(NOTE THIS IS NOW DEMONSTRATION ONLY, NOT CORRECT COMPONENTS)
| References | Qty | Description | Manufacturer | MPN | Manufacturer | MPN | Digikey | Mouser | RS | Newark | Farnell |
| U1 | 1 | IC MCU 8BIT 8KB FLASH 8SOIC | Atmel | ATTINY85-20SUR | ATTINY85-20SURCT-ND | 556ATTINY8520SUR | 68T3811 | ||||
| LDO | 1 | IC REG LDO 3V 0.15A SOT23-5 | Microchip | MIC5235-3.0YM5-TR | 576-2783-1-ND | 998MIC52353.0YM5TR | 71Y1742 | ||||
| U2 | 1 | IC LED DRIVER CTRLR DIM 10MSOP | Texas Instruments | LM3409MY/NOPB | LM3409MY/NOPBCT-ND | 926LM3409MY/NOPB | 7615678 | 14R4586 | 1735797 | ||
| L1 | 1 | FIXED IND 15UH 14A 14.4 MOHM SMD | Vishay Dale | IHLP6767GZER150M11 | 541-1287-1-ND | 70IHLP6767GZER150M1 | 7487615 | 13T1269 | 1845594 | ||
| D1 | 1 | DIODE SCHOTTKY 60V 30A POWERFLAT | STMicroelectronics | STPS30M60DJF-TR | 497-12421-1-ND | 511STPS30M60DJFTR | 8290456 | 97W2993 | 2325863 | ||
| Q1 | 1 | MOSFET P-CH 30V 14.9A TDSON-8 | Infineon | BSC084P03NS3GATMA1 | Infineon | BSC084P03NS3GATMA1 | BSC084P03NS3 GCT-ND | 726BSC084P03NS3EG | |||
| C1 | 1 | CAP CER 10UF 25V X7S 0805 | Murata | GRM21BC71E106KE11L | 490-10496-1-ND | 81GRM21BC71E106KE1L | 8851764 | 96Y9268 | 2611935 | ||
| C2 | 10 | CAP CER 0.1UF 16V X7R 0603 | Yageo | CC0603KRX7R7BB104 | 311-1088-1-ND | 603CC603KRX7R7BB104 | 6698763 | 68R4769 | 432210 | ||
| Cf | 1 | CAP CER 1UF 16V X7R 0603 | Yageo | CC0603KRX7R7BB105 | 311-1446-1-ND | 603CC603KRX7R7BB105 | 68R4770 | 1458900 | |||
| Cf2,Cin,Co | 10 | CAP CER 10UF 50V X7R 1206 | Kemet | C1206C104M5RACTU | Kemet | C1206C104M5RACTU | 1276-6767-1-ND | 603CC206KKX5R8BB106 | 14N2184 | 2581103 | |
| Cf2 alternate | 1 | CAP CER 220UF 6.3V X5R 1206 | Murata | GRM31CR60J227ME11L | 490-13970-1-ND | 81GRM31CR60J227ME1L | 55Y9932 | 2494472 | |||
| Coff | 10 | CAP CER 470PF 50V X7R 0603 | Samsung | CL10B471KB8NNNC | 1276-1094-1-ND | 7665238 | |||||
| JMP | 1 | RES SMD 0.0 OHM JUMPER 3/4W 2010 | Yageo | RC2010JK-070RL | YAG3380CT-ND | 603RC2010JK070RL | 98K7919 | 9235523 | |||
| R1 eswitch | 10 | RES SMD 360K OHM 1% 1/10W 0603 | Yageo | RC0603FR-0736KL | 311-360KHRCT-ND | 603RC0603FR073K6L | 68R0080 | 1799338 | |||
| R1 clickie | 10 | RES SMD 36K OHM 1% 1/10W 0603 | Yageo | RC0603FR-0736KL | 311-36.0KHRCT-ND | 603RC0603FR073K6L | 68R0080 | 1799338 | |||
| R2 eswitch | 10 | RES SMD 47K OHM 1% 1/10W 0603 | Yageo | RC0603FR-0747KL | 311-47.0KHRCT-ND | 603RC0603FR074K7L | 5047363 | 68R0098 | 2146120 | ||
| R2clk, Roff | 10 | RES SMD 4.7K OHM 1% 1/10W 0603 | Yageo | RC0603FR-0747KL | 311-4.70KHRCT-ND | 603RC0603FR074K7L | 5047363 | 68R0098 | 2146120 | ||
| R5 | 10 | RES SMD 4.7 OHM 1% 1/8W 060 | Vishay | MCT06030C4708FP500 | Vishay | MCT06030C4708FP500 | RNCP0603FTD4R70CT-ND | 594MCT06030C4701FP5 | 96Y9432 | 2614446 | |
| Rf2 | 10 | RES SMD 3.9K OHM 1% 1/10W 0603 | Yageo | RC0603FR-07390KL | 311-3.90KHRCT-ND | 603RC0603FR0739KL | 5046916 | 68R0081 | 2143821 | ||
| Rf3 | 10 | RES SMD 2.7K OHM 1% 1/10W 0603 | Yageo | RC0603FR-07270KL | 311-2.70KHRCT-ND | 603RC0603FR0727KL | 68R0067 | 2136427 | |||
| Rsns | 3 | RES SMD 0.075 OHM 1% 2W 2512 | International Resistive | LRC-LR2512LF-01-R075-F | International Resistive | LRC-LR2512LF-01-R075-F | 696-1670-1-ND | 66LR2512LFR075F | 7717792 | 88K2583 | 1254661 |
It's also possible to feed it alternate MPN's for each row so that the cart will get filled for all vendors.
It is complimentary to this:
https://greasyfork.org/en/scripts/19082-digikey-export-cart-possibly-to-bom. Which exports digikey shopping carts. Must install greasemonkey first.
Ah.. yes, Now I remember being confused about THAT when I saw it before. I now got C1 and OTC confused... well, because there is no OTC in this driver! Never mind. C1 is I guess only a bypass and maybe useful for the bleeder. Somehow I had that right in my parts description, just a not-so momentary lapse of reason.
Very nice work, I am busy today but I will sit down and check out those items later along with tweaking the driver to see about removing the jumper and squeezing a 1206 cap in there.
Also curious how arrow will compare in the final price outcome. Particularly with free shipping they have now.
Funny, that Texas Ace wants free shipping from Arrow when Mouser is in his backyard…
I honestly have only ever made one order from mouser, all I remember about it is that it was just so so. Prices were a bit higher then digikey, the website was far harder to navigate then digikey (although massively better then arrow) and the shipping cost was a bit cheaper but not significantly so IIRC.
My biggest issue with shipping is that out of all the orders I have made shipping is generally at least $10 for some parts that weigh all of an ounce and should cost all of $3 to ship.
When I only need $7 worth of parts and spend $10 on shipping, that should have cost $3, that bothers me.
Not to mention that to date Arrow has been cheaper on 90% of parts I have compared (they also have a price guaranty apparently, although not sure how it works).
Mouser is in Mansfield, you could drive over and pick stuff up and pay zero shipping.
They also have an option to use USPS for shipping at the lower rates, it’s not really clear though and you almost have to ask for it.
I buy almost all my components from Mouser. Have built hundreds of FET drivers with parts from them, a few times I’ve gotten stuff from DigiKey and the shipping costs were similar. Then the DigiKey site got difficult to access and I quit using them altogether.
Yeah so I was getting things all mixed up with the OTC momentarily and yet C1 does seem to play a role in this and the point of adding a controlled resistance maybe is even more clear. There's some weird stuff going on there. Without C1 I wouldn't think R1 matters for OTC, it just the highest resistance path to ground. Reading the docs it's not at all clear to me that attiny will shut down consistently, but I don't know. It seems like going with a 10x or 100x higher capacitor for OTC and a parallel resistor would put the discharge RC time entirely into our control and decouple it from all the side effects of every voltage and leakage in the whole system. I bet all this stability voodoo of minor changes here and there just dissappear. It also should allow to get rid of R1 and R2 entirely in direct drive non-zener lights without impacting OTC.
I'm seeing now this could be tested in a 1S non zener light without changes just by removing R1 and shorting the R2 pin to the OTC pin to create the RC. Then just have to choose the right OTC and R2 for desired RC. I've got a $0.50 0805 220uF cap picked out already. There may be cheaper options at 100uF or so.
Analog version?
So this thing is basically an analogish driver with a digital click controller and took a little thought (we'll still have to see) to cram that together. However, it's also possible to ditch the MCU entirely and just replace the Iadj stuff with just an ldo, pot, cap and resistor or two. The pot could be mounted in place of the e-switch for a fully analog light. Of course clicks have some use, always knowing really what mode you're in, so you know what to expect for heat and runtime, and some features like battery monitoring, thermal control etc are nice. But simplicity and analog control are also very attractive features that us humans tend to find comfortable. I don't know how hard it would be to find a nice pot knob that could fit on say a Q8. As for battery monitoring, we could undervoltage shuttoff back to the LM3409 (lol, I just asked about removing it, not even gone yet). And I think the LM3409 has some kind of thermal shuttoff built in as I recall, maybe pretty extreme though.
Interesting, I knew they were in Texas but didn’t know they were in DFW.
Although Mansfield is still a good drive from me. DFW is a huge place and just keeps getting bigger! You can drive for 1.5 - 2 hours in some places and still be in DFW! And thats without traffic.
Now at 3 in the morning on a toll road on the other hand, that time can be cut down to about 20 minutes…….
I use digikey simply because their website makes sense and you can narrow down the parts you are looking for far easier. Mouser is several steps behind when it comes to this.
In my case I best it would cost me the same in gas to pick it up as to ship it.
First off the OTC is a non-issue for this driver as it will be setup as an E-Switch driver in virtually all cases. It is not used for an e-switch.
Also the voltage divider can indeed be removed and the internal reference used with 1S setups but not with anything higher.
I also forgot that for e-switch lights we generally use 47k/220k voltage divider. Needless to say I do not deal with e-switch lights much.
Interesting idea, doubt many would use it but never know what someone would do with such an idea.
In this size at least yes. I momentarily forgot that earlier when I was looking at circuits instead of the board, and with all the discussion of it. I might raise the idea in another thread.
Yep, and it makes it a simple place to test this RC idea. Once my hot air station gets sorted, I might just give it a go. I've got all the bits, enough for two to compare for that matter.
Yes, so I'm not sure this is settled. I went with 360k/47k because we had strong confirmation of 36k/4.7k working well for 4S clicky. That will give the same divider obviously, and there are no OTC issues, so I thought that should be fine. Most of the early adopters will have the 220k on hand if needed anyway, so worst case is we change it and learn. Anyway, we can certainly change the part list if we're sure. I'm still not.
About the jumper:
So I’m probably missing it, but I just can’t see how that lower right quadrant could ever be ground. The upper right is + and the upper left is - and in 4s all other battery contacts are not ground. (the ground of a battery maybe, but not the ground, any raised voltage will due for the uv pin). I’m assuming there will be a jumper connecting the bottom two pads then.
For 2 S one of each of the bottom right and bottom left must be plus and minus. The mid voltage plane must be at the tail. There’s no other possible way. But I can’t imagine why the lower right would be ground. That would require connecting diagonal pads which is not simple to even do. The only thing that makes sense in 2S the lower right is connected to hot and lower left to ground, with vertical jumpers or traces on each side.
I’m wondering if you forgot to flip the board over in your head when you said that’s ground. If I’m confused, ok, but if I’m not, the jumper thing is real simple so maybe worth double checking.
I still think we should redo the voltage divider to whatever is ideal for the voltage in this case. Very few people have the components on hand for high voltage builds as it is so not a big deal to start over in this case.
Am I right that 4x the R2 should be roughly what we need to get the same reference voltage for the MCU with 4x the voltage?
So it would seem that an 47k/880k ish would be what we need?
Here it is:
Unfortunately this is upside down. But your markings confirm my understanding of where the jumpers go. Looks to me like a simple via will work great.
I had not really though of stealing some midpoint voltage. I suppose it would work to do that actually.