Lpc2000

Sean wrote:

>Unfortunately the source that I am using for most of my components doesn't 
>carry that regulator.  However your idea got me thinking.  From another 
>suggestion that was posted, the TPS61041 regulator chip is about 1/2 the 
>cost of the TPS61041, provides much higher current, and requires a similar 
>number of external components (and has a feedback line).  Would the same 
>method of adding a 100k resistor to the feedback line and to a PWM output 
>on the micro work here?  I don't see why not.  Can you see anything wrong 
>with this idea?
>
>  
>
Pretty much would work.  The idea is to set the feedback such that when 
no external disruption (PWM) signal is present, it will be at the low 
end of the desired range.  Then, when the PWM signal is introduced, it 
sucks (sinks) some current out of the feedback sense line tricking the 
regulator into thinking the output voltage is falling.   The regulator 
then accelerates dumping more current into the output circuit to raise 
the output voltage.

The actual mechanics may be such that you may have to add a small value 
of capacitance into across the feedback pin to filter the effect of the 
PWM rate.  This cap may be needed to steady the output voltage and avoid 
excessive ripple?  I suspect that the capacitor would then act as 
something of an integrator.

The principle is the same for any regulator that uses a resistive 
feedback (or where you can add a resistive divider), you are modifying 
(upsetting) the feedback voltage on a constant basis and the regulator 
will track your disruption.


Regards,

TomW






-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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