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Thread: Design challenge - switching regulator - update
picon face BY : Russell McMahon email (remove spam text)

>1. The voltage source is a pedal alternator/generator, sort of thing that
>to be used for flying doctors service in the Aussie Outback.


>You aren't making
>transceivers for New Guinea missionaries perhaps? Maybe a piece of exercise
>for a gym.


>2. The output from this is nominally about 10-12 volts at full load/optimum
>pedal speed. The problem arises because the voltage can go to about 130V no
>load/fast pedalling, but also the gear needs to operate at less than
>pedal speed.
>3. You need a stable output of around 9 volt at about 600mA whatever the

Yes more or less.

>It would seem to me that you should be limiting the maximum voltage to a
>value that you can work with by sticking a hefty zener diode across the
>generator output, say 25-30V, to act as a sink for excess energy.

No unfortunately.
The load needs to be set by the equipment with user feedback and adding
zener or other dissipation at this low a  level would add excessive
undesired loads in some modes.
In fact the absolute maximum "reasonable" voltage is probably 80 to 100
volts. Load is controllable via software (FET PWM)  and I intend to add load
under software control if voltage exceeeds some upper limit. The only people
liable to do this would be playing around for fun "how fast can I pedal this
thing on no load" and no useful features would be lost by presenting them
with a slowly increasing load above a certain speed.

>Just what sort of generator is it? If using a car alternator, the diodes in
>these are usually rated at about 50V, and do not like running without a
>limiting load (read battery).

Custom designed special - details not discloseable at this stage. I'kll tell
you all about it after the first 10,000 have been sold.

The change in the power supply is a late alteration occasioned by factors
outside my control.
Doing it is not TOO hard
Doing it ultra-cheaply is always a challenge.


           Russell McMahon

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See also: www.piclist.com/techref/power/priswitch.htm?key=switching
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Subject (change) Design challenge - switching regulator - update

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