As usual, Olin brings his quiet knowledge to the scene. And I will ponder the question "Is the cup full after 5 RC time constants or not?" Bill ----- Original Message ----- From: "Olin Lathrop" To: "Microcontroller discussion list - Public." Sent: Tuesday, November 08, 2005 5:30 AM Subject: Re: [EE] capcitor charge time > Bill & Pookie wrote: >> The capacitor will charge to 70.7% of the available voltage in 1 RC >> time constant. > > No, the value is 1 - 1/e = 63.2%. > >> The capacitor is considered to be fully charged after >> 5 RC time constants. > > This is an arbitrary choice of what you consider close enough. The > capacitor of an R/C filter is never fully charged to the input value. > It's > an exponential decay that never actually gets there, so the question is > really how close is good enough for the context. Saying that it's > "considered fully charge after 5 RC time constants" is misleading at best > without context. > >> In your case, after 18 seconds. > > Actually in his case it will never get there by a long shot since the B-E > junction will start conducting around 500-700mV. That's whay I answered > how > long it would take to reach 700mV in a previous post. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist