Re: 100kHz SMPS control

On Dec 16, 11:10 am, "Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:
"Nico Coesel" <n...@xxxxxxxxxxx> wrote in message

news:4764f8d1.1078194641@xxxxxxxxxxxxxxxxx

MooseFET <kensm...@xxxxxxxxx> wrote:

On Dec 15, 1:34 pm, "Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote:
"Jamie Morken" <jmor...@xxxxxxx> wrote in message

news:BUO8j.1099$hQ3.685@xxxxxxxxxxxx

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

cheers,
Jamie

You have to be careful doing that. We had to redesign a piece of gear
that
used the system 8051 to control a -48 to +5 converter. Blew about 6
transistors before the software guy got his code right. It would be
worthwhile to have some hardware gating to prevent doing something real
stupid.

..and that was on an 8051 which is very easy to code for. It wasn't a
DSP or a PIC which can be a lot harder to code on.

Doesn't matter for a real embedded software engineer.

I am sort of surprised that the software guy didn't dream up some way
to fully test his code in a more protected environment.

Now you are making sense. Test first then try in a real-life circuit.
Still, software like this should be written in a way the output is
limited by some hard boundaries based on the hardware. So when
calculations go wrong, the output isn't going beyond the limits of the
hardware.

Where the guy went wrong was in turning the OFF transistor ON before turning
the ON transistor OFF. They lasted a few minutes. Not obvious why he messed
with that part of the code at all; possibly to replace assembly code with c.

That, I think, explains it. Many people somehow think that code in a
low level language that works should be replaced with code in a higher
level language.

I still think that it is surprising that he put code that did that
onto real hardware. I often use a scope in checking and debugging my
code that works with low level hardware. I also tend to build in
interlocks so that things like attempts to turn on both transistors
forces things into a safe state. It usually takes very little extra
to do it.

Then again with no micros involved, we just blew something up in the
lab by turning a knob. We applied about 60V oooops!.




.

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 ...
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  • Re: 100kHz SMPS control
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