12 thoughts on “Simple PWM

  1. personally i have used this for quite some time now. it is quite reliable for some applications but is not to accurate if your controlling the pwm with anything but a resistor (or a pot) also i have been told its easier just to adjust pin 5

  2. the diode part is awesome!

    But now, the most of the pots out there are not precise enought for these use, maybe adding a resistor at each end could be very neat for cheapass servo control.

  3. A less common technique is pulse frequency modulation, which can be found in very efficient and low power switching power supplies. It lowers the switching losses in certain situations.

  4. How timely. I was just digging through my box of junk and found a LED product demo that has 3 faders and a pic controller to mix RGB on 3-color LEDs. I hooked the leads up to the Heath Kit (1962) Oscilloscope I just nabbed off craigslist last week (for $20) and low and behold, it uses PWM to dim each colored LED.

  5. @therian:
    In this circuit the frequency is controlled by the capacitor connected to pin 2, I think. I don’t think you can change the frequency by changing resistance in this case.

  6. @Sol & @therian:
    the 100k gives you the fill sweep to change the frequency the best way is the cap at pin 2 102 makes it switch faster and 104 switches slower

  7. @bob: pulse-frequency modulation (pfm) is really only good for low current applications, where switching losses are significant; typically, conduction (and other) losses dominant at higher currents.

    additionally, pfm can make emi more difficult to mitigate (at undetermined or over a wide frequency range); at higher currents the emi peaks are even higher, again a reason to (often) avoid pfm at higher currents.

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