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

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DB Custom
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My hot air reflow station bit the dust Sunday. Something in the iron handle shorted, the handle got hot, and turning it off didn’t solve the smoking issue at that point, had to yank the plug. The main unit smells bad so I know it’s fried. Just when I was really getting dependent on it, too!

DB Custom
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Any recommendations as to a good combination hot air flow station? I have an Hakko 888 soldering iron, so perhaps just the hot air station?

Anyone know if this X-Tronic 4040 is worth anything?

Looks to be decent, for a limited time they’re even throwing in a 12” gooseneck magnifier light…..

djburkes
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DB Custom wrote:
Any recommendations as to a good combination hot air flow station? I have an Hakko 888 soldering iron, so perhaps just the hot air station?

Anyone know if this X-Tronic 4040 is worth anything?

Looks to be decent, for a limited time they’re even throwing in a 12” gooseneck magnifier light…..

Y’all have me wanting to try to reflow my own stuff now. I don’t know if I want to get that involved though.

Texas_Ace
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Flintrock wrote:

I understand your point entirely.  It’s just not there right now.  Only just figured out what mosfet to use  yesterday and only worked out the leakage current issue on iadj a couple of days ago (before that I wanted 0.5s RC for soft transition as the premium touch, but without a huge cap it probably isn’t happening. I may still look into the huge cap options).  Mostly though, just have to sit down now and write up a short list mostly done above, but will make it more organized shortly.


 


 

Yeah, I totally understand and no pressure. I was simply saying to let me know when you get it all figured out so I could get it all put together into a nice easy-as-possible to understand post for people to try out.

You are doing good work, keep it up. Thumbs Up

Texas_Ace
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This is the reflow station I have: http://www.ebay.com/p/2in1-soldering-station-rework-hot-air-iron-852d-5-...

Well one like it, the first one that came up in ebay anyways.

It has served me very well. Not an issue with it to date. It works good, is stable and temperature control is good.

Only real complaints are it is not very high wattage so it takes a minute for it to heat up the iron and the iron is a normal china knock off without the best tips to heater fit (so it temp sags more on big things).

For the price though I am fully satisfied. A hakko is great but not 4x+ greater.

I find that the soulder you use makes a far larger differnce then the station. I recently got some new solder, after a buttload of research I settled on kester 63/37 #66/245 Flux in .6mm. It was hard to find but it was worth it. Flows super good, the iron stays clean and makes a great joint.

DB Custom
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When I first learned that I could actually solder it was because of the right solder and the Hakko 888 station. After that, I bought the big roll of Kester and now I stick with it, wont’ buy anything else. Kester solder paste too, have tried others and the dynamics of the Kester just hold it head and shoulders above everything else I’ve used.

Texas_Ace
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Kester is good indeed, just got to make sure you get the right stuff. Kester sells many many (way more then I first thought) types of solder and they all work differently.

The stuff I listed above is a no-clean solder with high flux content to allow easy hand soldering and good wetting.

The classic 44 kester works fine but you have to clean up the residue or it can screw up the parts over time.

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DavidEF wrote:
Texas_Ace wrote:
I am acting like anyone building these is a complete noob with no prior parts selection skills at all. Just a soldering station and the will to give building a driver a try.
This is exactly me! I need the list you’re trying to make for this reason. Thanks to both of you for working on this buck driver!

…and I too.

DB Custom
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I will tell of my own stupidity in the hopes that someone may learn something I obviously did not.

My cheap Yihua reflow/solder station has an on/off switch to power up the transformer in the rear of the unit. Individual on/off switches and temperature settings with digital readouts for each station on the front. I found that when I went to use the soldering iron Sunday the unit was in standby mode with – - showing on the screen. I fired it up anyway, and it overheated and smoked and died. Opening it up, the transformer overheated and melted down. This was obviously a result of my leaving it powered up overnight and then using it without a cool down. Now, I will say that there are 2 wires within the soldering handle that have all the insulation burned away, so something shorted in the handle and this may be the real reason it died. The handle of the iron was very cheaply made, with a plastic male/female thread connection that wouldn’t stay together.

I’m leary of purchasing another el-cheapo unit, but how do I know that a more expensive unit won’t still have these issues?

For the record, I didn’t buy this reflow station. It was in the modding kit I bought from Old-Lumens when he sold out.

Texas_Ace
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Interesting, I am always careful to turn mine off after I am done with it, I will continue to do that.

I don’t think I would get a more expensive knock off unit, from my research none of them seemed to really stand out as being better then the others. Go for a brand name or cheap IMHO.

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I think I found my hot air replacement, a XYtronic from the States (LF852D). Dedicated hot air, I already have the Hakko 888 so between the two I’ll be in good shape. Once you use the hot air station, there’s no going back! lol

Flintrock
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I just got a clone of a clone off aliexpress.  I'm going to go check my fire extinguisher now, lol.  I'll check for shorts from case to hot at least. I've been zapped by cloned chinese stuff before. 

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A little progress on caps, or at least on what doesn't exist.  

 

Until that's more ready.  I did have a thought.  It looks like there are still quite a few spare pins on that MCU.

 

It is actually possible to program frequency in the same way we program iadj.  It would require a second buffer cap that Cf2 charges from.  The buffer cap gets charged through a resistor (or possibly divider) from the mcu.  I say possibly divider because  Roff is always taking current  from the buffer cap anyway serving as the second half of the divider, pulled to ground during on time (by the IC, to reset Coff) , and never above 1.24 V during off time.  The fet duty cycle is very fast and coff discharge cycles won't impact the buffer cap.  Coff just sees a constant voltage source with an Roff impedance (exactly as it should), and the buffer cap just sees an average resistive connection to ground as if the second half of its voltage divider, as it needs to fix its voltage.  That average does depend on fet duty cycle, and so working out exactly what voltage and off time a given pwm makes has to be calculated still, but this doesn't need high precision either.

This probably isn't necessary for normal uses, but it could

a) offer some frequency vs power correction if it ends up useful (not clear)

b) simply allow frequency to be optimized without resoldering which if nothing else is useful while first figuring things out.

c) allow software reconfiguration if re-purposing the driver for a different voltage output.

 

Anyway, I'm still working on a shopping list for how things are now.  Programmable frequency could be a nice touch though. 

 

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Some of offtime RC values are wrong in the second and third tables.  It's a beta feature. I'll fix it when I do the final component summary.  

Flintrock
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Details on current adjustment here:

http://budgetlightforum.com/node/50413

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I'm going to need to know where we will set the LDO voltage in order to pick iadj components.  Am I supposed to decide this?  Are there any mcu issues to consider in this?  Parasitic drain etc? 

 

Things I can see (neither very relevant probably) are:

1) If we ever want to consider adding software frequency control or possibly other things, more is better.

2) However, there is an issue with 1S battery setups.  Normally you wouldn't use the LDO at all in those, but we are driving iadj off the LDO.  If you drive it off the battery you get voltage sag right from the start on a current controlled buck, which is just silly unfortunate.  One possible fix would be to still include an LDO and set it to about 2.8V  (or use a tinny85V and go lower yet, like 2.3V).  I don't actually see that this effects decisions now though since 1S battery will need a different voltage divider anyway.  Also using a buck from 1S battery seems not so useful to me anyway.

Texas_Ace
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1S battery not something to worry about, I do not see this being a good option over an FET or normal TA driver. So lets not worry about it for now.

The min voltage for the MCU is 2.7V officially IIRC, so anything over that up to 6V should do fine (I think the max they offer is 5v). Whatever works best for the buck would be ideal IMO.

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I suppose lower gives a little better control ripple. So maybe 3V is good.  I see the LDO uses the same 1.24V reference as the IC so we can use the same resistor values for LDO and IADJ.   I see.. now, you're using the fixed output versions.

 

I guess I also need to know the iadj PWM frequency.  I think 19 is typical.  Is there a typical exact number for that?  We do want it high of course.

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LDO resistor? I was not aware that the LDO needed or even could use a resistor unless you used the adjustable voltage version?

The PWM feqency changes some between outputs from what TK said. IIRC it was something like 31khz on 2 of the tripledown firmware outputs and the normal ~19ish on the other.

No clue as to how or why that is the case.

Flintrock
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Yes, I was confused, edited above. I guess I don't need exact PWM values.  So long as it's upward of 19 it should be fine.

Flintrock
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No plan on using attiny45 is there?:

 

From the manual's errata.

8.2.4 Rev A

• Too high power down power consumption

• DebugWIRE looses communication when single stepping into interrupts

• PLL not locking

• EEPROM read from application code does not work in Lock Bit Mode 3

• EEPROM read may fail at low supply voltage / low clock frequency

 

Too high power down power consumption Three situations will lead to a too high power down power consumption. These are:

-An external clock is selected by fuses, but the I/O PORT is still enabled as an output.

– The EEPROM is read before entering power down.

– VCC is 4.5 volts or higher.

 

Problem fix / Workaround ATtiny25/45/85 [DATASHEET] 21 2586QS–AVR–08/201

--  When using external clock, avoid setting the clock pin as Output.

– Do not read the EEPROM if power down power consumption is important.

– Use VCC lower than 4.5 Volts.

 

I'm not sure what "too high" exactly means or what "power down power consumption" exactly means (I guess power use when off), or if this is a general trend that just happens to be a bit worse in the 45, or maybe only got documented in the 45, or is just a bug in the 45 that doesn't apply at all to others.  The warning is removed from errata for later revisions so I guess it was improved or fixed.

 

I'm leaning toward 3V anyway. It gives a little better control ripple, slightly worse for potential design upgrades but can worry about that if and when.  And now there's this warning that makes me a little nervous. 

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That may actually explain why the tiny85’s had issues with the voltage spikes before the latest DEL component changes but the 25’s didn’t.

In this case there is no need for high voltage to drive an FET so I think 3V would be fine.

Flintrock
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Well, there are plots for off current vs vcc.    Attiny might drain the battery some in 100 years.

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This only seems to have applied to old versions of the 45.

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So what footprint are those small pads meant to be?  They measure .11*.04 inch by my pixel count.    Seems kind of a compromise of anything from 0603 to 1206.  Anyway, there's certainly room to widen Cf2 out to .06 wide.

 

I forgot to redo my cap searches with lower voltage ratings for the control caps.  That turns up 220uF caps.  There's one that's a $1.74 on digikey in an 0805 but it's only 4 volt rated.  For 3V low current, that would probably just about cut it.  There are also a couple of in 1206 that are 6.3V rated for $1.26.

 

A 220uF Cf2 makes it possible to  hit Iadj RC times of 0.33 s or a bit more, ie soft mode transitions, with only a small increase in resistance, leading to an 0.6% minimum current mode instead of 0.2.  I'm going to squeeze this on mine.  I'll might write it up as an alternative setup, because you can get 10uF caps for 0.30 or maybe less, and they work fine too.  The dollars add up on these things.

 

(The 220uF also makes software frequency control with 0.3% offtime jitter possible)

 

I ran numbers on a 1S batt setup for fun, with a vf curve added since it matters there.  The thing actually makes a nice 1S driver.  > 93% efficient on paper down to 0.5A or less.   In the middle modes, 0.5A to 1A,  linear is only about 70% to 75% efficient, so that's not bad.   93%/75% = 1.24.  That's a pretty big savings if it works out real.  The reason linear has been considered ok, is because its only competition is PWM'd DD.  And because, as you've pointed out, it makes light come out of the front end of the device, which is the main thing. 

 

 

 

 

 

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All of the small pads are standard 0603 pads, you can put 0805 components on them if you need to but better to have the correct pads.

If CF2 is the only one that would need a 1206 that could most likely fit but the rest are already as large as they can be and maintain any kind of proper clearances.

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That's the only one.  Well.. I'm aiming towards 1206 now for Cin and Co and I personally will squeeze as many 10uF caps in Cin as I can, certainly 3 will fit, just maybe 4.  I'll write it up for the designed way, plus some comments.  If you want to draw it as 3*1206 that's fine (not sure you can really draw it as 4).  Or could just make 2 solid rails and be done with it. 

 

The Rsens is what 2010?  Updated:  Ok, this appears to mostly be what's available. and yes, 3 seems right unless we want to push things very very close to burning up.   So I'll write something up.

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Even in the 10uF, selection is much more limited in 0603 than 0805. 

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Here is the component footprint list as it sits right now.

Cin is 1210, it could be swapped out for 3× 1206 it looks like but it is already too close to the edge for my liking. I actually want to pull it back some more in possible.

Rses is 2512 simply because it was the largest resistor I could find and they had the highest wattage ratings It could be shrunk to a small size obviously and I might need to anyways to get the edge clearance I want.

Here is an updated CF2 to 1206 (not reflected in the list). It works but is the very limit of what those component sizes can be

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looks good.  I was thinking you could move D1 a little down and then right (but not much) and then shove Q1 right and Cin over to the right a little for clearance.  I agree on Rsense when I looked at what's available.  Using two would be VERY tight.  Might end up with some burned resistors.  Anyway, Cin is ok with 2 by 1210.  I suppose if you really needed the space you could cut it back to 2 by 1206.  If left as is though, I'll try to pile a heap of caps in there with a wad of solder and see what sticks.  I'll write up the baseline as 2 though.

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