GekkoScience BM1384 Project Development Discussion

[richardamullens]

Although I do not expect it, it would be interesting to see the schematic of your power supply design.

Although it is a completely different beast, there is a schematic for a software controlled DC-DC converter at http://www.ti.com/lit/ug/slau597/slau597.pdf page 36 - for the new MSP432 launchpad.

I pretty much gave up on switched mode power supply design many years ago when I found that the 25V EPROM programming voltage I generated had a 1 microsecond 14V overshoot that instantaneously killed my EPROMs.

[sidehack]

Yeah, efficiency on that circuit would be pretty bad especially for low-duty-cycle applications. Also it's microcontroller-based, which can get tricky with software-defined frequency response if you want it to be really stable. A proper dev and testing of the code would take me a lot longer than just using a TL494 to do the same thing at least as well.

I measured the peak-to-peak ripple on our regulator, and also the peak overshoot, which would be on the charts. Typical instantaneous overshoot (which is a peak maybe 50-100nS wide) was less than 100mV. A bit of topography change and a high-frequency shunt capacitor, and some more bulk capacitance (I found my 47uF 1206 caps after I'd already full-range-tested it with some 22uF) would help smooth it out quite a bit.

One noteworthy thing was when the driver chip shifted into synchronous mode instead of skip/diode mode, usually around 650mV at low loads but as the load currents increased into the ranges these things will actually be running at, that threshold dropped somewhat linearly down below 600mV and by the top-end measurement it was starting in synchronous mode. This had a measurable effect on both efficiency and output ripple, as continuous conduction with a synchronous rectifier is way better than low-side-diode pulse skipping with hysteresis.

[richardamullens]

Thanks for the technical information
I am of course interested in what you are making - or I would not be here - but I think that switched mode design is very important for many other things - e.g. LEDs for hydro/aeroponics and electrolytic purification of Copper where, I believe a cell voltage of 0.25V is used - hence my interest in software design in place of standard chips.

[sidehack]

Right, switchmode is used in just almost everything these days. But a mathematically assured analog hardware solution I will always prefer over a software-only solution, especially where high speed frequency-dependent response is concerned. Why do an ADC sample and FFT and whatever else convolution processing for transfer functions when you can just put proper RC filtration on the line and be done with it? Everyone loves complexity these days, but complexity usually substantially decreases reliability and I'd rather have something reliable than something fancy any day.
Our TypeZero boards will have software-settable voltage control, but not because we have a fancy digital regulator. So far I'm designing around a flexible and reliable analog SMPS chip and probably put a DAC reference on it to do software adjustment. The stick miners don't need software-defined voltage. The complexity for that scale is stupid, so I'm just putting a smal trimpot on instead.

[richardamullens]

Yes, of course, you are right. A pot on the stick miner and a DAC on the type zero strike the right balance.

I'm a minimalist and sometimes software allows you to remove hardware - but of course there's a price to be paid for that in terms of software complexity.
The basis of my metal detector is at http://www.rhodamine.eu/~richard/cv/ew.jpeg my only electronics publication

[sidehack]

Snazzy idea there. I have zero electronics publications, so you're definitely winning.

The AntMiner U3 has software-definable voltage, but it uses some crazy TI digital driver that's buried under NDAs just to get a datasheet, and so is the probably-all-digital FET driver it chats with to get things done.

Yeah our engineering philosophy is definitely minimalist - or more precisely, minimal modularist. Find a simple and reliable thing to do the job well and use it; if the job is manifold, split it up and find simple reliable segments. Microcontrollers can be the simple thing, but you have to consider that though it's only one chip, a microcontroller is an incredibly complex and intricate circuit all its own. When we were looking at multiphase regulator design we looked at something like the TI driver chip on the Habanero, which can handle 6 phases with all digital monitoring and something something potatoes. It's pretty fancy. The thing incorporates a 32-bit ARM processor on top of a bucketload of ADC circuitry and some DSP segments I think.
But I think instead we're gonna use TL494s to do the heavy lifting, with a small microcontroller to generate synchronised clocking signals and control phase shedding where needed. Small code, few errors; easily modularisable, flexible and reconfigurable; anything time-critical is entirely analog. There's probably more compact and integrated ways to do it, and with a fast enough processor we could probably replace every piece of silicon short of the switching FETs with a single chip, but I'd have to be convinced that it was legitimately functionally better, not just easier.

I really like the TL494. I don't know how popular it is anymore, in a world of highly integrated and automated everything, but that chip is a beast. So many functions and basically all of them are broken out to pins. Lots of control, lots of flexibility, zero programming requirement. For the record, 2/3 of my college education was Computer Science and Computer Engineering so I'm not scared of the programming, I just tend to look for non-computational solutions first. A couple weeks ago Novak combined an entire board design of mine into a $0.70 microcontroller and about five interface parts, and it's clearly the better option. These things happen.

[richardamullens]

Thanks for the idea of the TL494 - I was surprised to see that the datasheet was last updated in Jan 2015 and there was an application note written for it last year http://www.ti.com.cn/cn/lit/an/slva666/slva666.pdf
I've only used the UA78S40 which is more expensive and available in fewer packages - so your device wins

[sidehack]

Yeah, I like to think of the TL494 as the 555 of SMPS controllers. I'm not familiar with the part you mentioned.

The TL494 has dual error amplifiers, so you can wire up an overcurrent protection on it natively, or overtemp, or whatever. And an external deadtime control pin that basically allows for additional error amplifiers to be tied in to reduce the duty cycle when necessary. Switching frequency control up to 300KHz and dual outputs that can be run in parallel or push-pull. Buckets of those chips were used as half-bridge forward converters in old ATX supplies, I don't know if they're still that common anymore though. They can be driven by an external clock, but the only thing I don't like about the chip as a whole is the external clock has to be a sawtooth. Makes sense since that's what PWM is compared to, but it'd be easier to tie 'em together if they could synchronise off a square pulse. I really like that they don't use a fixed internal reference voltage, which is what makes software adjustment possible when you use a DAC. And then you're not limited to whatever lowerbound the fixed internal reference gives - typically 0.6-0.8V which you mentioned 0.25V so that'd be out by 99% of driver chips.

Working on the miner project is the most fun I've had at work since about a year and a half ago, when I was spending the first 8 hours of the day on hardware refurb stuff (the real job) and the next 8 hours designing and building a 7V->150V push-pull forward converter for a nixie tube power supply around the TL494. That was a good week.

The chip being used on the Compac is an IR3899, which I noticed last week is the big brother of the 4A-rated regulator on the Bi-Fury stickminer (I forget its part number).

[CanaryInTheMine]

Glad to see you guys are making some progress!!  If you need anything else feel free to ping me.

[sidehack]

Nothing except time, currently, and you're not really capable of that kind of thing. I'm probably gonna focus on hosting maintenance tomorrow and hand off Compac dev to Novak for software stuff, maybe get initial Amita board design done and get back to the TypeZero regulator work which I haven't touched in a few weeks. I guess I do have some paperwork to take care of for Bitmain as well.

[Unacceptable]

Here ya go...open CAREFULLY,it slips away if you don't  

[richardamullens]

The IR3899 looks awesome and I had not appreciated that the TL494 doesn't have an inbuilt reference - thanks.  I'm still minded to try to roll my own software converter though (for 0.25V).  Last night I connected a 100W 660nm LED to a 24V supply and watched as the current rose from 4 to 4.3 Amps before I bottled out - later I got the spec from China and it said the Abs max rating was 3.5 A but it still seems to work fine.  It was attached to a 30x14 cm heatsink but perhaps it got to 55 Celsius - uncomfortable to hold so I'm going to need some fans ...

Keep up the good work - what you're doing is very interesting to hear about.

[novak@gekkoscience]

We have hashrate coming from a BM1384 on our breakout board.



Note freq = 100 so expected hashrate of 5.5GH, it's a bit low but it moved up shortly afterwards.

--
novak

[valkir]

This is awesome! Great job novak!

Check your PM 

[sidehack]

In case anyone's wondering, here's a chart of the regulator efficiency as tested. It still needs work, as I'm having trouble getting more than about 3W out of it before it starts to cut out. I've already ruled out undervolt protection, and it's certainly not overcurrent, so it might be temperature-related. More testing is needed, but I want to be able to push it to at least 6A at 0.75V and right now I can't get 4A at .75V out of it.

Also, yes, the regulator is currently attached to a populated BM1384 breakout board and capable of operating. We exchanged high fives until our hands went numb. Tomorrow's Tuesday sandwiches will include celebratory ice cream.

Once I get the regulator ironed out, I have a few changes to make to the Compac PCB. We'll need to test chaining and see how hard it'll be to get two chips in series to talk to each other.

[Xian01]

We have hashrate coming from a BM1384 on our breakout board.

That's tremendous ! Congrats !

Love following your updates.

[Unacceptable]

AWESOME!!! 1st of the baby steps 

[Searing]

AWESOME!!! 1st of the baby steps 

ah a potential 'toy' for me in the making...(I'm such a miner slut!) but I must admit have 'tempered' my ways to either 1) baby miners or 2) frigging great
deals on used stuff.....

so perhaps "demon asic purchases" of any 'real' danger are a thing of the past......

(moderation.......my new mantra...although I have to mumble it constantly when seeing neat miner porn like yours)...hey its a start on the road to recovery right?

[vs3]

We have hashrate coming from a BM1384 on our breakout board.
http://s15.postimg.org/hrku64kfv/hashing.png

AWESOME NEWS! CONGRATS!
And keep up the great geek pron coming!

[jekecoin]

We have hashrate coming from a BM1384 on our breakout board.
http://s15.postimg.org/hrku64kfv/hashing.png

AWESOME NEWS! CONGRATS!
And keep up the great geek pron coming!

Yeah! Awesome, I hold my money , and Beauty board