pic microcontroller discussion list wrote:
> As I noted, I'm aware of 555, 556 and similar. The issue is turning
> them into a working solution at fair price. Linearity tends to suffer
> where you are using exponential cap charge - but may be OK. Getting a
> full 0%-100% PWM range is often more challenging. I can play with
> them myself (and yet may) - i was interested in seeing if anyone
> popped up with a working superior solution rather than just the
> skeleton ideas.

maybe I can repay your help a little. I did a prototype soft-start
circuit for a 120Vdc motor. Circuit gets the full 0-100% range. It
uses an LM2903 + current source charging a cap to generate a ramp.
The comparator discharges the cap to reset the cycle. The trick is
using diodes instead of resistors for feedback. frequency is
determined by the cap value and charging current, so you can adjust
to your needs. For lower cost, the current source can be replaced
by a resistor. The other section of the 2903 sets the duty cycle.
It worked  like a champ for what I needed. Unfortunately, someone
else beat me to it :(  So I don't even have to clutter the list
with attachments (although would be glad to send off-list). I'll
just direct you to http://www.4qdtec.com/pwmmod.html That's pretty
much what I came up with, except minor differences (my ramp goes
to 2/3Vcc,the artivle 1/3Vcc). But the theory is the same. The
author even mentions replacing the resistor with a current source....

Not sure what the commercial implications are of someone having
published this, though. It is a commercial site from someone
selling motor drives. This are my thoughts: The concept of
creating PWM is certainly well known today, and it doesn't take
a great leap of imagination to replace a charging resistor with
a current source for greater linearity. The innovative part is
the diode arrangement, which I hit upon while playing with this
circuit a year or two ago, and the author's inspiration came from
a customer...


>
> So far the LPC901 seems the most promising processor based solution.
> I like my 4060/339 idea for a non-processor alternative 0 the digital
> ramp would overcome the cheap opamp setup problems.
>


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