Its not really a matter of cost, its more about making use of what I have on hand and learning abit as I go. I will learn more using parts that are not 1 chip solutions. Sure it may be more work, but I used those one chip solutions for years in synths, never learned much from them.
To each his own, I guess it's my aversion to using 20 parts when I can use 1 doing the talking! Personally I like the simple solutions, much easier to master all of the part's "personality". It sounded like you wanted something really easy, which gludged timer IC based PWM is neither easy nor reliable.
-isn't Digikey right down the street practically?
Sure, about 250 miles down the road.
Ok, I only asked because you could probably get your package overnight with ground shipping. Much better than my 1500+ miles away...
So are there any pitfalls going with an opamp triangle oscillator (comparator or comparator integrator type) and then going into a comparator to set the PW. Most any decent opamp comparator should be able to drive the MOSFETs gate should it not? Unless there is some major flaw in this idea I am most likely going to just build it tomorrow and tweak it until it works. I am ready to start winding in style.
The oscillator and comparator are fairly easy. Use good parts around the ramp generators or your ramp might induce a slight jitter, but that might not be of any matter to your needs. Also, like I mentioned earlier, the timer IC was never meant to drive mosfet gates, you might want to use some kind of buffer setup between the IC and the gate. It takes a lot of charge to pump the gate of a higher power mosfet, sometimes up to an amp if you are attempting to slew the gate at really high frequencies. At lower frequencies your dv/dt will suffer and you'll have a much longer transconductance period than you should if your gate drive is slow and/or weak. This will cause your FET to heat up signifigantly and ultimately you will get a slight pulsing of the motor due to the resistive drag during the extended transconductance periods. If for nothing else than your sanity, this is one of the reasons I suggested a part designed for the duty.
There is a lot more to it than just getting a motor to go around and around, especially when your FETs overheat or you reach some crazy oscillation frequency where all your problems come together(the voice of experience..). But again, I speak of high power/high speed dc brushed motors.
Some of the others around here work with the BIG boys, multiphase ac, etc.. I'm sure they will definately tell you the same as I.
Good luck, and have fun though!
