R200 is a 0.2 ohm resistor.

Sounds good, thank you for checking.

GL! Here’s your chance to prove why you need to horde that stuff

R200 is 0.2 Ohm: .9 = .18 / .2

Oops. Thus proving… wow, good thing we don’t depend on me around here! I got moving too fast. Let me go back and edit (cross out) a few things… OK, done. I didn’t cross out where I was doing the datasheet math, but that was wrong too since I used incorrect units. The datasheet’s math would be more like 0.25/0.2 = 1.25A

Thanks for correcting me.

The buck drivers I have worked all use .25 , but (more efficient) drivers from sandwich shoppe have used .05 sense… so I was using .18 based on the current measures here.

This will all get sorted out sooner or later here, thanks.

Not a bad idea of course, when I was using the wrong units it was just really confusing to me where 0.18 came from. Now that I realize my mistake your logic is clear!

I fished around on the internet a little and it seems that the “LEDA” chip is definitely the QX9922.

http://club.dx.com/forums/forums.dx/threadid.1205677
[quote=desolder]

It’s the QX9920:

http://www.szroya.com/uploadFile/download/200886204048427.PDF

The IC is rated for 24V, but the input capacitor is only rated for 16V. So it appears the “5V-12V” description is the correct one.

If anyone is curious, here’s the thread claiming that it’s the QX9920, apparently from a representative of the company:

http://translate.google.com/translate?hl=en&sl=zh-CN&u=http://bbs.dianyuan.com/topic/581194&prev=/search%3Fq%3DLEDA%2BSOT-23-6%26hl%3Den%26client%3Dfirefox-a%26hs%3DuZE%26rls%3Dorg.mozilla:en-US:official%26prmd%3Dimvns&sa=X&ei=S0cUUPWkOcbsqAGBl4CYCw&ved=0CFoQ7gEwAAp
[/quote]

desolder is misleading when he says that the chip is rated for 24v, the chip can run on 2-6.5v. The diagram in the datasheet shows a 2.5v - 5.5v Zener Diode in use along with the appropriate resistor in order to keep the chip inside that range.

No doubt that's what some of the extra stuff on the PCB in this thread is. I don't see the advantage of QX9920 over QX5241.

Hi,

Sorry, too many posts have gone by, so I’ll answer the ones I know about here so we can kind of start fresh:

- [wight, I think]: That was a good call on the solder blob, i.e., you were right, that all 3 components (one end of the toroid, one end of the 151 component, and one end of the brown component) are shorted together, both the blob-less and the blob-ful board.

- [wight, again, I think]: I didn’t find an R200, but I did find an R300, so I figured I’d try that, parallel. From the post above, R300 would be .3 ohms?

So, I have R200 and R300 in parallel, i.e, so equivalent of 0.12 ohms.

Is that correct?

Anyway, I tested the driver after that, and BINGO, Iemitter on high went to ~1.62 amps (from previous 0.90 amps)!

So:

0.2 ohms => 0.9 amps

0.12 ohms => 1.62 amps

I took the Vbat/Vin quite high, > 10V, I think, but I got excited, and didn’t really watch the correlation of the Ibat/Iin vs. the Iemitter, but I did see Ibat/Iin start dropping at some point as I raised Vbat/Vin.

I’ll do that later.

So, given the above, what resistor value do you all recommend to replace the R200 “safely”?

Thanks,

Jim

EDIT: Can we get this driver to 3 amps at the emitter, or maybe even higher?

EDIT 2: And yes, I still do have all 5 modes…

It’s possible, based on your results, that the sense voltage listed in the datasheet is no longer accurate. Maybe it’s using the same sense voltage used by QX5241, approximately 205mV. Or it could be 180-290mV, who knows. Really it’s just as likely that somewhere in this mess of a driver there’s something messing up the normal sense voltage setup.

I’d dig up an R100 and put that in parallel with the R200 (for 0.0666666666666 Ohms). That should give you approximately the current you want. (maybe 2.7 - 2.9A based on what we’ve seen so far, maybe 3.75A based on what the datasheet claims (250mV sense)) If current is too high, discontinue use until you’ve increased resistance again ;-).

Pushing this current too high will generate problems related to the SS34 diode, the inductor, the no-doubt-crappy FET, etc.

EDIT: yes, you are correct about R300 and about R200 and R300 in parallel.

I just wanted to confirm: I need to look for a 0.1 ohm, 1206 resistor, right?

Fastech has them:

http://www.fasttech.com/products/1002/10007371/1615807-1206-0-1r-smd-precision-resistors-100-piece

Thanks.

I saw those earlier, but they’re marked “R10”, vs. “R100”. What’s the difference between an “R10” and an “R100” resistor?

Nothing, the “R” represents a decimal point. R10000000 would also be the same thing, they are just trailing zeros.

It **looks** like a 1206, but I’d measure it if I wasn’t sure.

I’d also still consider an order from Mouser. For <$10 you should be able to get out of there with a decent assortment of precision sense resistors. They’ll get to you faster and if you choose the right values you’ll be in a good position to tune your output exactly as you want.

OTOH I always feel a lot of pressure to pile everything I can into a Mouser order so I don’t have to order again right away. With FT you just buy what you want, one item at a time.

Hi,

BTW, for the record, I’ve added the emitter leads and tested the other board (the one with the blob) and it’s performing the same way as the first one did before I added the R300 resistor in parallel with the original R200 resistor.

So my paranoia about the blob of solder was unfounded :)…

I’ve ordered some of the R100 and R200 from Digikey, just in case, so I’ll have a pile of them :)… Shipping actually wasn’t bad… they apparently ship via USPS first class now, so it was about $3+ for the shipping.

Thanks,

Jim

Good.

If you’re game, let’s go ahead and stack R200, R200, and R300 on one driver for 0.075 ohms. That will be a good test to see how the sense voltage scales at close to 3A before you place any orders.

Sure, I think :)… Let me give it a shot…

Jim

Hi,

Ok, it’s done. I was seeing about 2.8 amps at the emitter from when Vbat was at about 4V+!

Too late already though. I had already ordered some resistors (some .1 and some .2 ohms).

The lower we take the resistance, the higher Vcsn seems to be! (2.8 * 0.075 = 0.21)

R100 and R200 in parallel should put you at 3.15A+

~6.4v Vf + ~0.21v current sense = regulated to maybe 6.61v? At that point your batteries are dead anyway. That sounds pretty decent to me. Assuming the driver survives of course!

BTW, could you post the actual dimensions of the driver? Diameter & height is what I’m looking for. TIA

Small buck driver, pushing 3 amps and nothing’s burnt yet…

Thanks for the write-ups, ohaya. Now we just need to see if blinkies can be nixed easily.

BTW, could you post the actual dimensions of the driver? Diameter & height is what I’m looking for. TIA

+1. Also, what’s the diameter and height of the toroid, both including and excluding the winding? :bigsmile: