I had a similar problem with a 7805 running from a 24V source, the load was a 555 timer, 4020, 2716 eprom and a 74ls373 driving 3 opto triacs IIRC. not much load, but the 7805 had to be mounted on a 1.0oC/W heatsink to keep it working, since then I have mad a design rule, all 7805's are fed from 8 Vdc. I know they have a wide input voltage (I have stack (not sure of PN) that were 7805 compatible that had 120VDC input rating). These days unless cost is an issue I either use a multi tap transformer, or I use switching regulators. Regards, Kat. ____________________________________________________________________________ /"\ ASCII Ribbon Campaign | K.A.Q. Electronics \ / - NO HTML/RTF in e-mail | Software and Electronic Engineering X - NO Word docs in e-mail | Perth Western Australia / \ | Ph +61 419 923 731 ____________________________________________________________________________ ----- Original Message ----- From: "TH" To: Sent: Friday, November 09, 2001 11:07 AM Subject: [EE]: PIC overheating a 7805 ! Hi, I've got this system up and running where a series of modules containing 16F628 (running @ 20MHz) and individually fed by LM7805 (TO-220 package) are all run from the same 24VDC line (long run) coming from a switching supply. Each module also has an LM7806 for driving an R/C Servo motor. All my modules work fine except that the 7805s are running rather hot even though the R/C motors are pulling much more current from the 7806 than the little PIC is from the 7805. The 7806's temperature is ok though. At first I thought that it would only be necessary to heat-sink the motor's regulator but know I think I might have to do the same with the PIC's. I can almost burn my finger from the 7805 ... I understand that 24V isn't the optimal voltage to run the 7805 from if I intended to draw a lot of current from it but National's datasheet says that it can take up to 35V and considering the very low current consumption I don't understand why it is overheating. I suspected the length of my supply line but running a module even a few minutes on a short length gives the same result. Besides, the voltage drop is barely perceptible and I have pretty good wire gauge. Could my choice of caps for the regulators be causing the problem ? I have one 470uF 35V electrolytic before the 2 regulators and a 0.1uF ceramic cap after each of them. thanks, Tobie Horswill thorswil@exmachina.qc.ca -- 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