Comments on: Simple PWM

By: carlton

carlton — Tue, 18 Nov 2008 02:03:25 +0000

@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.

By: therian

therian — Tue, 18 Nov 2008 02:03:03 +0000

changing cap is good enough, thanks

By: biozz

biozz — Mon, 17 Nov 2008 19:59:26 +0000

@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

By: Sol

Sol — Mon, 17 Nov 2008 19:50:10 +0000

@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.

By: therian

therian — Mon, 17 Nov 2008 19:22:22 +0000

is there a way to add another pot to control frequency also ?

By: Sol

Sol — Mon, 17 Nov 2008 18:45:06 +0000

I like this. So many projects use microcontrollers as overkill when a 555 timer will do the job.

By: Xeracy

Xeracy — Mon, 17 Nov 2008 18:03:38 +0000

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.

By: Bob

Bob — Mon, 17 Nov 2008 15:37:12 +0000

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.

By: ex-parrot

ex-parrot — Mon, 17 Nov 2008 08:02:05 +0000

huzzah. afrotech slowly consumes the internet.

By: jimmythecow

jimmythecow — Mon, 17 Nov 2008 06:18:42 +0000

afroman does it again!!

By: James P. Wack

James P. Wack — Mon, 17 Nov 2008 05:49:54 +0000

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.

By: biozz

biozz — Mon, 17 Nov 2008 03:50:51 +0000

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