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Thread: Design challenge - switching regulator
www.piclist.com/techref/power/priswitch.htm?key=switching
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face BY : Roman Black email (remove spam text)



Ok Russell, got the lateral bit of my brain working
now, your input range of 10v - 130v is pretty big for
a 9v supply. Will need huge range of PWM width, which
shoots you in the foot for designing inductors
and getting good filtering. Seems more suited to
a fixed pulse width variable freq system, with some
type of wacky filtering...

How about run your load from a NiCd pack, at about
9v. Then you can use a cruder switchmode system
to dump enough power into it to keep it's voltage
reas constant. I noted your 9v - 7.5v output range
and i'm assuming regulation is not critical.
Now your inductor doesn't have to "filter", really
it's just there for switchmode efficiency, so
it is cheaper and less critical design.

Now you go and ask for it to run from a 4v input?
So you want step-up too? I'd go for a fixed pulse
width system, (i've seen this in OLD switchers,
it allows optimum design for filtering as the
pulse width is stable over a huge input voltage
range) into a small toroid transformer, (gives
isolation) and simple half wave rect on output.
Decent filtering on output, or maybe NiCd as
mentioned.

Regulation is on/off, it dumps pulses until output
voltage is reached, then stops pulsing. This will
give pretty good regulation while being safe and
cheap for isolation.

Think of it more as a way of dumping pulses of
energy from the primary, until the output is full.
Could use simple self excited primary, (with some
mechanism of turning it off when output is "full")
would probably work from 2v up with the right primary
semi. Whew. My lateral brain cell is tired. ;o)
-Roman






Russell McMahon wrote:
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