Reply by John Larkin November 27, 20182018-11-27
On Mon, 26 Nov 2018 23:34:47 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >news:en8ovdda4800lktv8ad1qmgb05jslb4bbg@4ax.com... >> >> I did note discontinuous mode, which someone snipped. But it wouldn't >> be hard to write code for continuous-mode control. I've done CCM >> switchers with comparators or schmitt trigger gates as the control >> elements; just limit the max duty cycle and it usually works. > >Doesn't seem to be in this exact branch of this thread. > >CCM with duty limiting only works as long as you consider the load as part >of the control system and not an adversarial unknown. Or for certain values >of "usually" and "works". > >Tim
I've got to admit that power supply design is more difficult when the load hates you. This works fine https://www.dropbox.com/s/8ggd03k0arhosu2/Neg_Reg_Inv.gif?dl=0 But a Cuk is a little quieter. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by Tim Williams November 27, 20182018-11-27
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message 
news:en8ovdda4800lktv8ad1qmgb05jslb4bbg@4ax.com...
> > I did note discontinuous mode, which someone snipped. But it wouldn't > be hard to write code for continuous-mode control. I've done CCM > switchers with comparators or schmitt trigger gates as the control > elements; just limit the max duty cycle and it usually works.
Doesn't seem to be in this exact branch of this thread. CCM with duty limiting only works as long as you consider the load as part of the control system and not an adversarial unknown. Or for certain values of "usually" and "works". Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by John Larkin November 27, 20182018-11-27
On Thu, 22 Nov 2018 16:16:00 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

>On Thursday, November 22, 2018 at 11:09:31 PM UTC+1, Tim Williams wrote: >> "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >> news:taqdvd983sbci31sulfkda0fagihjvm603@4ax.com... >> > What is the cheapest uP that has an ADC input? One of those and a >> > three cent mosfet would make a nice boost switcher; just needs a >> > little code. 30 cents for the uP and fet and a diode maybe. Serial >> > interface is probably free. >> >> Guessing, cheapest with >200kSps isn't going to be as competitive as you're >> thinking. >> >> That's basically what the stupid phaux-analog controllers are anyways. >> >:( >> > >Silabs Busybee EFM8BB1, comes in at below 20 cents, and has 800kSa ADC, plus deadtime enabled timer, 2% voltage reference > >Cheers > >Klaus
That's a heap of stuff for 20 cents. The 8051 opcodes are morally repugnant, but if they are hidden under a c compiler, they are almost tolerable. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by November 27, 20182018-11-27
On Mon, 26 Nov 2018 08:55:58 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>tabbypurr@gmail.com wrote: > >> the usual objection is what if it crashes > >The usual solution is to use an MCU with sufficiently sophisticated hardware >to cram your switcher into that. Even a tiny PIC16F1709 >has all the required circuitry to take care of 2 current-controlled >SEPIC converters. I've done that, also for the purpose of LED >powering (14W in each channel). The software part is there just >to configure the hardware blocks and run the slow voltage loop >(if needed at all). And for digital brightness controll + other >bells and whistles.
I've been suggesting these, here, for a while. They're really slick parts.
> >With a PSoC you can even move your PID into hardware, but I'm afraid >the cost would not be 20 cents, even if blackmailing the CEO.
The PICs will do PID.
Reply by Piotr Wyderski November 26, 20182018-11-26
John Larkin wrote:

> That's interesting. Set a PWM duty cycle a bit higher than needed, and > just do bang-bang control whenever you get around to it.
You can go a step further and require the bang-bang event to happen at least once per some predefined interval. If it doesn't, you have a short circuit or a feedback network failure. You shut down the system in either case and report malfunction/perform delayed restart, whatever fits you. Back then I had believed that *this* is the way all the switchers work, have learned the "proper" PID control about 7 years later. Best regards, Piotr
Reply by John Larkin November 26, 20182018-11-26
On 26 Nov 2018 12:21:05 -0800, Winfield Hill
<hill@rowland.harvard.edu> wrote:

>Piotr Wyderski wrote... >> >> Tim Williams wrote: >> >>> If you're okay with exploding transistors and shitty control >>> loops, sure, sample just voltage. :-) >> >> Tim, we are speaking about a 350mW power level and powering a LED. >> I bet that even an unregulated boost with a fixed PWM ratio would >> do the job. > > It does use CCM, especially when starting from zero, and there > needs to be an input current limit that's not far above the > operating input current. This drive up the parts count and > area for a comparator or uP solution.
The uP version could ramp up pulse width and check that the output voltage is increasing properly. Supervised soft-start. The LEDs won't pull much current until the voltage gets high, so it should be easy to test the basic boost mechanism at low duty cycles. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by Winfield Hill November 26, 20182018-11-26
Piotr Wyderski wrote...
> > Tim Williams wrote: > >> If you're okay with exploding transistors and shitty control >> loops, sure, sample just voltage. :-) > > Tim, we are speaking about a 350mW power level and powering a LED. > I bet that even an unregulated boost with a fixed PWM ratio would > do the job.
It does use CCM, especially when starting from zero, and there needs to be an input current limit that's not far above the operating input current. This drive up the parts count and area for a comparator or uP solution. -- Thanks, - Win
Reply by John Larkin November 26, 20182018-11-26
On Mon, 26 Nov 2018 00:45:40 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >news:l5fjvd1029vg0ij38he6pkmt3k5h8cdube@4ax.com... >>>If you're okay with exploding transistors and shitty control loops, sure, >>>sample just voltage. :-) >>> >>>Tim >> >> If I know the voltage and control the gate drive, I know the currents. >> > >Only in DCM. > >In CCM, there's that pesky "...PLUS A CONSTANT!!" from Calculus. > >Tim
I did note discontinuous mode, which someone snipped. But it wouldn't be hard to write code for continuous-mode control. I've done CCM switchers with comparators or schmitt trigger gates as the control elements; just limit the max duty cycle and it usually works. You can always buy a smaller inductor. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by John Larkin November 26, 20182018-11-26
On Sun, 25 Nov 2018 23:46:43 -0800 (PST), tabbypurr@gmail.com wrote:

>On Sunday, 25 November 2018 23:05:30 UTC, bitrex wrote: >> On 11/25/2018 05:07 PM, John Larkin wrote: >> > On 25 Nov 2018 12:50:37 -0800, Winfield Hill >> > <hill@rowland.harvard.edu> wrote: >> > >> >> John Larkin wrote... >> >>> >> >>> If the input voltage is fixed/known, or measured, and we >> >>> have a discontinuous switcher, the inductor current is >> >>> predictable. So we can dump a controlled shot of energy >> >>> onto the output cap every pulse. Knowing the output >> >>> voltage and the applied power, we know the output current. >> >> >> >> OK, and the input currents too, should work. I'm >> >> usually reluctant to dedicate a significant fraction >> >> of my processor's time to a simple job handled by a >> >> cheap sot-23-6 part. But, it's true, while the boost >> >> converter is charging the processor has to wait anyway, >> >> before doing anything else. Then when the voltage is >> >> up, LEDs on, and the processor is busy, I could use a >> >> timer channel to provide PWM, checking the voltage every >> >> now and then to be sure it hadn't deviated too much. >> > >> > My suggestion was to use a cheap uP as a switcher controller, where it >> > has nothing else to do. You could probably sneak in a serial or SPI >> > interface, which wouldn't take much compute power. >> > >> > Just a thought. It wouldn't be worth writing the code unless the >> > savings were substantial and the quantities high. >> > >> > >> >> idk what the counter-argument was exactly, that it can't be done or....? > >the usual objection is what if it crashes
Well, don't do that. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by John Larkin November 26, 20182018-11-26
On Mon, 26 Nov 2018 08:24:17 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>John Larkin wrote: > >> Is there a uP? Make your own software controlled boost converter >> maybe. Mosfet, inductor, diode. > >+1. > >If the output voltage quality isn't critical, a simple on-off >regulation with a fixed PWM duty cycle can work well. Used it >20 years ago to power a 12V motor out of a 5V rail, ~10W. Worked >OK. Li-Ion has a pretty flat discharge curve, that would help a lot. > > Best regards, Piotr
That's interesting. Set a PWM duty cycle a bit higher than needed, and just do bang-bang control whenever you get around to it. -- John Larkin Highland Technology, Inc lunatic fringe electronics