----- Original Message ----- From: "Pic Dude" To: Sent: Wednesday, April 03, 2002 10:45 PM Subject: Re: [EE]: 7805 heating up... > So my other question now is ... what are the alternate strategies > to reduce or eliminate this heat? > > Possible options so far are... > > (1) More heatsinking... > > (2) Reduce power consumption. Are there any tricks to setting > unused I/O pins to certain values, etc? I've turned off unused > features, but I'm sure I have a lot to learn on these PIC's. (BTW, > I'm using a single 16F872 with one A/D input. Other port A > pins are set as analog inputs, but all tied to ground). All other > port pins are used as inputs or outputs. > > (3) Drop the 12V to a smaller value with ??? and then let the > 7805 regulate it better. > > Or...??? 5w 7v2 zenner in line in (12v Zenner input 7805) or 7808 then 7805 or LM317 as constant/curent souse. Regards Art. > > Thanks, > -Neil. > > > ----- Original Message ----- > From: "Olin Lathrop" > To: > Sent: Wednesday, April 03, 2002 3:05 PM > Subject: Re: [EE]: 7805 heating up... > > > > >> > > Using a 7805 in a vehicle (basic circuit with 1 inline rectifier diode, > > then small cap on input of 7805, 33uF on output). > > The max calculated current draw for the circuit is approx 200mA. > > Hardly seems like enough current to strain the regulator (1Amp), > > but it gets hot enough that I cannot leave my finger on it for more > > than 5-10 seconds. > > > > Should it get this hot? > > << > > > > Do the math. You left out a lot of particulars, so I'll assume 14V going > > into the regulator. That leaves a voltage drop of 14V - 5V = 9V. 9V x > > 200mA = 1.8 watts. Yup, that'll toast your finger assuming a TO-3 package > > without a heatsink. > > > > > > ***************************************************************** > > Embed Inc, embedded system specialists in Littleton Massachusetts > > (978) 742-9014, http://www.embedinc.com > > > > -- > > http://www.piclist.com hint: The list server can filter out subtopics > > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics