hi i designed a pulse width modulator using 555 the problem
is that the magintide is not stable,i simulated the circuit in multisim and with a breadboard using osciloscope plz can someone help me?

 

Are you saying that the simulator and the breadboard with real components BOTH produce that waveform?

 

yes(( i can't find the problem

 

I honestly don't know how to get that output from a 555. Scope the voltage on the timing capacitor. Maybe it will yield a clue.

 

Curious, where did you get that circuit?

A common and different version is here:


John

 

Or, closer to home, there's the 555 PWM section of Bill's blog. (Oddly, that link fails for me right now. Hopefully it works for you.)

 

Hello,

Here is the entry to the 555 blog of Bill Marsden:
http://forum.allaboutcircuits.com/blog/leds-555s-pwm-flashers-and-light-chasers-index.378/
Scroll down for chapter 5 for the PWM.

Bertus

 

Curious, where did you get that circuit?

A common and different version is here:
(pic removed)

same picture both locations playing around with that circuit now and it works like a charm

 

same picture both locations playing around with that circuit now and it works like a charm

Which "both." Obviously, the schematic I posted and the schematic in the link for its source are the same, as one would expect.

However, the schematic posted by the TS is different. Look at the output/gate drive. In the TS's design, the "output" (Pin3) is used presumably for the gate drive, at least that is the source for the oscilloscope trace. In the DPRG design, "Discharge" (pin7) is used. Pin 7 is used in several designs as an output, but it is not the same as pin 3.

John

 

I'm still at a loss to explain how you could get that trace on the output pin of a 555. I would say it's a measurement artifact (such as a shifting ground) but the OP says the simulator gives the same result.

 

Which "both." Obviously, the schematic I posted and the schematic in the link for its source are the same, as one would expect.

thanks John, deem my interpretation of 'A common and different version is here:' incorrect

i read as A common (as image displayed) and assumed and different version is here: as another version.

kind regards,

Tom