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Topic: 556 PWM help (Read 2177 times) previous topic - next topic

supercap

I used the following schematic for a 555 (I used 556) controlled pwm circuit, with variable duty cycle (pot).
I looked at the output through an oscilloscope. The pwm works. I am getting the proper duty cycles, but on a DC level (aprox. 6v w/ 6v supply, 1.5v pk to pk). This has happened with other circuits and only with the 556 (555 seems to work fine). I need to use the output to modulate another 555 for IR (reset pin).
Can anyone explain? This is the schematic I used
http://www.josepino.com/circuits/pwm

raron

I'm surprised that works at all when using the 555. As far as I can see, the 1k resistor should be between +Vcc (marked +6~9V), and the center tap on the pot. This point should then also be connected to pin 7 of the 555 (discharge. Or the equivalent on the 556).

supercap

I put up the wrong schematic, here's the one that worked
http://www.instructables.com/id/Simple-and-dirty-Pulse-Width-Modulation-PWM-Wi/#step1
I was taking my output from the output pin and ground. Output has to be taken from discharge and vcc.

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