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[DPRG] PWM circuit question

Subject: [DPRG] PWM circuit question
From: Dennis Clark dlc at frii.com
Date: Wed Jan 15 07:15:42 CST 2014

No problem. 

The cap discharges primarily through pin 3. That is the pin with a low voltage on it. You are correct in your observation that pins 2 and 6 are current paths, but they are inputs and are high impedance paths, which means very little current flow. Pin 3 is an output, which is a low impedance path, and so pin 3 is the path along which most of the current will flow. The low impedance path then is the primary means to discharge the capacitor. 

Did that help?

Dennis Clark

On Dec 12, 2013, at 8:15 AM, Tony Ennis <tony.ennis at twc.com> wrote:

> Hello, first time poster.
> I found a PWM circuit on the DPRG site:
> http://www.dprg.org/tutorials/2005-11a/
> I am a perma-newb with electronics, and I like to at least try to understand how things work.
> My question is with this statement:
> "When the output (pin 3) goes LOW, capacitor C1 starts to discharge through the left side of R1 and D1."
> C1 discharges... to where? how?  I'd expect a ground.  If pin 2 or pin 6 of the 555 is the place, then current doesn't have to flow through D1.  So that makes no sense.  Help please!
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