Re: 100kHz SMPS control

On Dec 15, 3:29 am, Jamie Morken <jmor...@xxxxxxx> wrote:
Hi,

I was initially thinking of designing a 100kHz SMPS with using 200kHz
ADC feedback of the output voltage and current fed into a DSP which
would directly interface to the fet drivers, and using cycle by cycle
regulation based on these readings,

Don't do it. That way lies madness!

You should initially be thinking about what exactly you are trying to
do that can't be done with a much-much simpler chip than a DSP.

If you are using a DSP or a PIC or anything like that you need to
protect the system during the time that the part takes to wake up and
start working. For development and likely also in production, you
need to add hardware to keep things safe if the code goes wandering
off into the weeds. This usually ends up as complex as just using a
switcher chip and controling it with the DSP or micro.


but I think this may be very
difficult to read these signals cleanly without them being noisy
from all of the switching noise.

If you want high frequency information the spikes are a big problem.
One thing that can work for you is that you can trip the converter at
a time when nothing is switching.

So as an alternative I am thinking
that it would be better to use a SMPS controller IC with voltage and
current feeback inputs, which seem to be easier to get to work than a
200kHz ADC in this environment :) and use its output PWM signal as an
input into a DSP or CPLD/FPGA for controlling the primary side
fullbridge to drive the transformer.

Don't put any programable part in the important path of the
converter. Use a PWM controller and the like for the whole loop and
then use the DSP to command the controller what to do. If you need a
little more logic in the path use real logic gates or perhaps a
22V10. Any logic more complex that that should have you questioning
what you are doing. I have found that most 22V10s wake up sane. Very
few FPGA or CPLDs work right before they get their morning coffee.

This reduces the flexibility of
the power supply as the current and voltage limits are set in hardware
rather than software, unless some DAC/comparator etc setup is used to
drive the SMPS controller IC feedback,

Chances are you don't need the comparitor. You can set the important
points with DACs and op-amps. A portion of the proportional feedback
can be done by resistors on the PWM chip. The integral feedback can
be done inside the DSP or micro.

but it is easier to trust a
SMPS controller IC rather than a complex ADC/DSP software system to
control a power supply. Perhaps a tradeoff would be a controller IC
with a digital interface to allow on the fly adjustment of the
voltage and current limits as well as the PWM frequency etc. Does an
IC like this exist? I think it would be pretty useful! Any people
here ever use high speed ADC and software to control an SMPS?

Do you mean successfully?


cheers,
Jamie

.

Relevant Pages

  • Re: 100kHz SMPS control
    ... ADC feedback of the output voltage and current fed into a DSP which ... that it would be better to use a SMPS controller IC with voltage and ... input into a DSP or CPLD/FPGA for controlling the primary side ... worthwhile to have some hardware gating to prevent doing something real ...
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  • Re: 100kHz SMPS control
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    (sci.electronics.design)
  • Re: 100kHz SMPS control
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    (sci.electronics.design)
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    (sci.electronics.design)
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