Thanks for the replies people. > And the 12V transformer would be it's RMS rating > So you would have/need over 1`5.5V across C1 I think that's what confused me most. The diagram said 12V secondary on transformer and 9.1+5 = 14V. Why didn't they just use a higher voltage regulator instead of the zener + 5V? I promise no more questions about this after this one. Chuck H. ----- Original Message ----- From: "p.cousens" To: Sent: Sunday, August 17, 2003 10:06 AM Subject: Re: [EE:] 24vdc from a 15vdc psu > And the 12V transformer would be it's RMS rating > So you would have/need over 1`5.5V across C1 > > Peter Cousens > cousens@biscit.biz > > > -----Original Message----- > > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU] On > > Behalf Of Wouter van Ooijen > > Sent: Sunday, August 17, 2003 2:28 PM > > To: PICLIST@MITVMA.MIT.EDU > > Subject: Re: [EE:] 24vdc from a 15vdc psu > > > > > If you can tolerate a novice question, I'll appreciate an > > > explanation of how > > > the output of the 7805 circuit in the > > > http://www.mitedu.freeserve.co.uk/Circuits/Power/alarm_psu.htm > > > diagram is 14v1. Thanks in advance if you will. If not, I > understand. > > > > The output of the 7805 is 5 Volt, reffered to its ground pin. The > Zener > > keeps the ground of the 7805 9.1 Volt above ground (that is, if the > > zener is operated at its nominal current), so the output of the 7805 > is > > 14.1 Volt above ground. > > > > Wouter van Ooijen > > > > -- ------------------------------------------- > > Van Ooijen Technische Informatica: www.voti.nl > > consultancy, development, PICmicro products > > > > -- > > http://www.piclist.com hint: The PICList is archived three different > > ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.