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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?
DLC

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Dennis Clark
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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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