The Texas Buck driver series, Q8 / Skyray King 2S/4S buck driver RELEASED!

For the e-switch that is what the switch pads are for. For an LED output there is the pad next to the MCU for control an indicator LED and the bleeder resistor gives options for a uncontrolled LED. Not sure there is a need for anymore?

I see. I wondered if it could power through the switch contacts. Didn't know if the mcu put out enough juice. The BR pad is a bit small, but yes, it works.

Oh, power the LED through the switch wires? Hmm, not sure about that. Kind of doubt it. Generally you run the LED to another pin anyways on both the switch and PCB, which is what the pad next to the MCU is for.

Come to think of it, there is enough room to enlarge the BR, so I might as well do that, either 0805 or if it will fit 1206.

Yeah, but if that's the reason for enlarging it, there are probably easier places to make a big batt+ pad. Either way though. On the other hand if you forget the ground pad on BR, there's even more room to just get a hot. It's all good.

Oh my shopping list still has a JMP in it I think or at least my text does. At some point I thought I should remove it, then realized, one jumper is needed for the 4S battery connection anyway. Not sure if that's still a good size, or if wire is better anyway. Wire is surely fine, so it's not a big deal anyway you slice it, but we could include a few reasonably sized jumpers in the list.

Yeah, I need to check and see what size is needed to make the jump effectively. Although basically anything will work, the ones you listed will surely be large enough and if cheap they should be fine.

$0.14 each and $1.20 for 10. I wouldn't call that very cheap. 1206 are $0.24 for 10.

Just checked it and the 1206 should work fine, or 1210.

I bought one of these as a fairly random impulse, not necessarily greatest or cheapest:

It's got the d2pak or something similar FET and diode. Those are 470uF electrolytic input and output caps, however the output is shorted with some sizable SMD cap, most likely ceramic. That seems to be a common practice power through output transients while maintaining low ESR of the ceramic.

The input cap is shorted by an "M4" diode (you can see it on the bottom of the board). That's interesting. It seems to be rated for 1A and basically shorts reverse polarity input to ground. However I don't how that wouldn't fry in a couple of ms, so I'm not sure it really serves as reverse polarity protection.

The whole thing is 26mm by 60mm including pots, terminals, and the giant caps, however it's a two sided board. Of course there's no mcu. Or I don't think so. There is an IC, that I'm fairly certain is a buck controller. I've tested it so far on a wire short, and it was horribly inneficient, (like 10% efficient) but that was waay into DCM and way below the diode Vf. The regulation control got very wonky down there too. I also tested it at 2A output to an XM-L2. It was 87% efficient, for input anywhere from about 4.5V up to 17V, and seemed to control very reasonably. The input power really didn't change. So it seems to work ok for that.

For the wire short I pushed it up to 10A for awhile and it handled it pretty well inspite of that huge inefficiency. I didn't have a chance to see how long it could keep it up or really measure how hot it got het. Of course that wasn't much actual power, I think 7W total power as recall, about 0.7 output. I don't have any good way to test it at high power at the moment. On the other hand most of the losses depend more on current than power.

It would kind of be interesting to see what other cheap similar sized bucks are capable of. Of course as for cheap, they have the advantage of mass production. I'm kind attracted to some of the simple analog controls and self oscillating designs just for the simplicity of it, but it's not clear how much cheaper any of it really is. You still need a good inductor, good fet, good diode, and for anything this big, of course the big board. There are some voltage regulated designs that drop the sense resistors.

It's hard to see how to make anything cheap on a one off DIY scale though. Of course the board is nearly half the price for one-off. It can be worth thinking about what it costs to make 100 though and maybe in some design MTN would do it eventually so it's not only one-off costs that matter. Boards get 3x cheaper automatically when you build more than three at a time, and many of the components get cheaper if you build 10. It might be possible to build 10 for the price of three. This is not necessarily meant to be correlated to my thoughts about simpler designs.

Anyway, I'll update the jumpers in the cart shortly.

Hmm.. I suppose with protected cells or a fused input supply, that input-shorting diode, rated to 30A for a couple of ms, would likely give enough time for the protection to kick in, and may prevent frying the IC in that case.

I have a few buck converters like that. They usually have ripple and are not that great but work fine for what we do with an LED. How they are able to do that so simply is what I don’t know. Same for flashlight drivers, not sure how all these buck drivers you see work so well and are so cheap. I don’t see much we could really cut costs on except the inductor.

Looks like the jumpers are going to get more expensive, not cheaper. Those Yaego's and many others are surprising only rated as <50mohm and a couple of amps. Our sense resistors would make better high current jumpers than those. I found some vishays 1210 or 1218 at 12 or 20A rated, < 4mOhm:

http://www.vishay.com/docs/20043/crcwhpe3.pdf

But those are going to be about $0.41 a piece. Personally, I'd probably just strip some 14awg solid wire. But I can put some Vishay's in the cart. I'll look a little more for something cheaper, but that's probably about it.

Actually the 1218s are $0.59 each.

I think I'd go with them though as a stock smd suggestion. I need to know if that 0.18 width will interfere with the batteries though. The 1210's have the same resistance rating, probably just don't take heat quite as well.

Wow, the 2512's are rated for about 4kW ... for a microsecond. Yeah, at 4mohm that's a thousand amps. Good to know, just have to set that turbo timer a bit short.

You’ll need some VERY high drain batteries too!

I personally would also just use a solder bridge / wire myself. I have not forgot about this, just got another project I am working on right now that is a bit more pressing (got to figure out a driver for the BLF GT).

It's not bothering me at least. I'm not ordering anything for it until I have a Q8 in the mail.

I hooked that cheap buck between 4S LiIon and a 12V halogen. Put about 40W through it. Roughly 95% efficient, scratch that, battery was falling off during measurement, just remeasured with fresh battery, getting 100% within the precision I can measure, probably limited to about a percent by clamp meter current accuracy, anyway, it's darn efficient, but that's basically direct drive. It remained very cool (it's only 3A). It's an infineon FET, so that's a good sign. They're about $.50 each for 1000. They'er actually To-220's which are a bit bigger than D2paks because of their heat sink.

Anyway, this halogen is a great way to test. I've a couple of housing and higher power bulbs, could probably get up to 130 watts with two over-voltaged 50W bulbs. They can take straight 16.8V without frying for a couple of hundred hours anyway.

Which buck are you talking about? I must have missed that.

The little one from the Amazon link we discussed a few posts up. Nothing to do with flashlights really, just observations of a cheap buck. I haven't hooked it up to a scope. It's may have enormous ripple for all know. Anyway, there's no particular point to the story.