The mica insulators don't seem like it would work properly cause they would insulate the screw heads, from the outer surface of the tabs, but not the threaded body from the inside of the hole on the tabs. UNLESS, I was using some sort of plasic or nylon screw, which I'm not sure would take the heat. Cheers, -Neil. -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tan Chun Chiek Sent: Monday, July 01, 2002 1:17 AM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]: Regulator grounds... Yes, you are correct about the diode bridging. heatsink is not necessary as i believe 12v is only used as a program mode selector in a programmer and draws next to no current. However, do that note that 78xx might go out of regulation if there is very little load on the output, so consider adding a load resistor. those transparent mica insulator, (not sure is that a correct name) are used for insulating TO220 package from heatsink. Regards, Tan CC ----- Original Message ----- From: "Pic Dude" To: Sent: Monday, July 01, 2002 2:00 PM Subject: [EE]: Regulator grounds... > Using 2 regulators (Tait programmer), both in TO-220 packages: > 7805 and 7812. I was planning on securing both of these to the > same heatsink, back to back, but not sure this is such a good > idea now... > > The datasheets confirm that the metal tab on each device is > connected to ground, which I will take to mean that it is > internally connected to pin 2. But the 7812 has its ref pin > offset with 2 diodes (to raise the output to over 13V), so if > I connected both metal tabs together, then the diodes would be > bridged and useless. > > So am I assuming correctly here? I probably don't even need > heatsinks on the 7812 --- I need to calculate that. > > Cheers, > -Neil. > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads