I'm trying to create a PWM signal to dim an LED. I came a across this circuit: When I tried it out on a breadboard powered by a 5v supply coming from my USB Digilent Analog Discovery, it worked great. However when I tried to power it up from a 5.3v power adapter that plugs directly into the wall, I get a short increase in voltage on the PWM output signal. On the oscilloscope, it looks like this: What's interesting is that the voltages reach up to about 5.8v, 0.5v more than what I'm even supplying the op-amp.
Moreover, when I set the duty cycle to 100%, it becomes apparent that the voltage increases have a frequency of 60Hz, the same frequency as the AC coming from the wall.
I tired to see if the voltage from the power supply was fluctuating between 5.3v and 5.8v but after measuring it seems that it does output a constant 5.3v.
What could be causing this weird behavior??? Thanks!