Re: microprocessor controlled SMPS

From: mike (spamme0_at_juno.com)
Date: 06/07/04 

Date: Mon, 07 Jun 2004 16:35:20 -0700

artem_bond wrote:
> Hello all.
>
> I have a principal question about SMPS with microprocessor. SMPS
> without microprocessor (UC3842) is simply. But I'm thinking about
> putting feedback to the CPU, more protections from stupids and other
> things. But, using microprocessor could be dangerous because it's
> could be hang-up by EMI or errors in firmware. I'm have a big
> experience about ground layout, supervisors, wDod timers and other
> things. By any way, some times it's was not enough especially inside
> SMPS.
> So. I need a something like ?smart? drivers. I thinking about
> protection:
> 1.Current transformer. (very fast, but could not prevent transformer
> saturation)
> 2.Hall-effect sensor after rectifiers, before snubbers. (Slow, but it
> could protect IGBT even if they opens together)
> It's ok. I seen drivers who have ?over current? input with trigger.
> But I have no idea about how to connect push-pull driver to PWM, and
> how to make protection from IGBT through current, (I will limit
> death-time outside microprocessor with something like RC circuit).
> Ideally protection by measuring frequency (20kHz +- 1kHz) would be
> very good.
>
> Any ideas, appnotes? I'll use Atmel AVR microprocessor. And I will not
> use FPGA.

I've started down this road more than once. I always come back to a
standard swtiching power supply with a micro to control the inputs.
Micro looks simple, but by the time you add on all the failsafes, fixes,
workarounds, external sensors and limits, it gets more complex than
just using the PS chip in the first place.

We did build a charge diverter/shunt regulator for a solar power system
using just
a micro. But didn't care much about precise voltage, current, transient
response etc. Most of the hardware ended up in, you guessed it, the
failsafe stuff in case the micro locked up or failed.
YMMV, mike 

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