Forums

boost-converter trouble

Started by Winfield Hill November 20, 2018
Tim Williams wrote:

> (Ever more, these days, designs are -- I assume -- driven by digital > engineers, following specs written by other digital engineers, few if > any of whom have a nuanced, general understanding of control theory or > DSP.� It's all sausage inside.� You don't want to see it getting made.
True, but OTOH, if Win can accept a software solution, it means a micro is already there. So what do you need a boost converter chip for? It can be easily crammed into the software. Then implement any control strategy you wish.
> Such a device is presented in such-and-such way, following a block > diagram, and seemingly emulating an analog chip (which would do the same > job with fewer transistors, but higher development costs).
Some analog chips just aren't there. Try an interleaved DCM PFC controller for instance. Or a bi-directional buck-boost. Best regards, Piotr
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
John Larkin wrote:

> What is the cheapest uP that has an ADC input?
For this power level you don't even need an ADC, a comparator will do. ADC-based PID control is an unnecessary luxury and a waste of CPU cycles. Best regards, Piotr
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. Best regards, Piotr
Winfield Hill wrote:

> 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
Yes, make the job simple and try gating the PWM signal with a built-in comparator. Just try. This is not a mains-powered 500W switcher where it pays off to use a more advanced control algorithm, just a sub-0.5W LED power supply.
> handled by a cheap sot-23-6 part.
Which is unpredictable, as this thread witnesses. Best regards, Piotr
Tim Williams wrote:

> Only in DCM.
Going into the CCM land for the required 350mW would be an interesting adventure on its own. Accompanied with a synchronous rectifier, perhaps? ;-) Best regards, Piotr
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 NT
> Clearly building switching controllers of some type are what uP > manufacturers often expect people to do with their parts or why would > they include hardware dead-time generators with a bunch of 'em > > cheap uPs have compute cycles to burn nowatimes as compared to e.g. a > 6502, they're not your granpa's 8 bit. A 16 bit by 16 bit signed > multiply on an AVR 8 bit takes only around 200 clocks average _without_ > a hardware multiplier unit, you can run them to 20 MHz!
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. 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. Best regards, Piotr
bitrex wrote...
> >>> include hardware dead-time generators with a bunch of 'em >> >> some good part numbers? ...
Tell me about the hardware dead-time generators. -- Thanks, - Win
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