PWM Viewing with an oscilloscope

Discussion in 'General Electronics Chat' started by lmartinez, Mar 16, 2009.

  1. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
    I have a 100K square wave which is pulse wave modulated. When I view the 100k square wave, with zero percent modulation, it is perfectebly display on the textronix 2445A, 150M Hz oscilloscope. However, as the square wave is modulated (10-50%) I am not able to see a reasonable trace of the modulated square wave on the scope. Please advice if there is a way to utilize my oscilloscope to observe the modulated square wave and not just a bunch of random pulses. The square wave is being modulated by a 60 Hz Since wave. Thank you :)
  2. KL7AJ

    Senior Member

    Nov 4, 2008

    Indeed, this will be very difficult, if impossible, to trigger off of this signal. Your best bet is to just modulate with a VERY low audio frequency and observe how the pulse width changes. You might even modulate it with a very slow ramp signal, if your circuitry will pass DC

  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Try switching the trigger to "LINE", it will sync with the AC Supply, if you live in the US, That should get a stable display of something.
  4. lmartinez

    Thread Starter Active Member

    Mar 8, 2009
    Thank you guys:

    Indeed, I tested the circuit by varying the amplitude of a dc signal(rather than using a 60 Hz modulating signal) and the output of the modulated square wave did show the appropriate response.

    I will give it a try by switching the oscilloscope's settings to "Line". Yes, I do live in the USA.