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[DPRG] PWM circuit question

Subject: [DPRG] PWM circuit question
From: Rick Bickle rbickle at intconsys.com
Date: Wed Jan 15 10:49:24 CST 2014

Check the description of pin 3 in the tutorial. It has internal transistors
that switch the pin to either VCC or ground.

When pin 3 switches to ground (goes low), the current flows from C1 through
D1 and R1 through pin3 to ground.




From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
Of Tony Ennis
Sent: Thursday, December 12, 2013 9:16 AM
To: dprglist at dprg.org
Subject: [DPRG] PWM circuit question


Hello, first time poster.

I found a PWM circuit on the DPRG site:


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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