----- Original Message ----- From: "Mike Blakey" To: Sent: Monday, November 12, 2001 8:58 AM Subject: Re: [EE]: PIC overheating a 7805 ! > The power used and dissipated by the voltage regulator is NOT calculated that way. > the power dissipated by the device is approx. = (Vin-Vout) * quiescent current and > NOT load current. Check the data sheets! > >I beg to differ. I think you mix up power consumption and power diddipation. Power consumption is what the regulator uses to do the regulation, so to speak. That is very little indeed. But the dissipation is (Vin-Vout)*load current (plus the power consumption of course, but that is normally insignificant). Look at it as a (variable) resistor with a voltage difference of Vin -Vout, and a current = load current. If it was us you seem to think, no regulator would ever become hot and Ohms law would be violated... Regards, jan Didden > > > > haroldhallikainen@JUNO.COM on 09/11/2001 18:44:56 > Please respond to PICLIST@MITVMA.MIT.EDU@INTERNET@wtgw > > To: PICLIST@MITVMA.MIT.EDU@INTERNET@wtgw > cc: > Paper Mail: > Subject: Re: [EE]: PIC overheating a 7805 ! > > *** WARNING *** > > This mail has originated outside your organization, > either from an external partner or the Global Internet. > Keep this in mind if you answer this message. > > > 24V is a bit high! Calculate out the power dissipation > (24V-5V)*LoadCurrent. Take this (in watts) and multiply by the rating of > your heat sink in degrees C/ watt. This should give temperature rise from > ambient. > Another thing to watch for is oscillating regulators, which get hot. > Check the output on a scope and make sure you've got DC without a bunch > of RF. > Finally, consider a switching regulator. The inefficiency of using a > linear regulator to go from 24V down to 5V is pretty impressive. > > Harold > > > FCC Rules Online at http://hallikainen.com/FccRules > Lighting control for theatre and television at http://www.dovesystems.com > > ________________________________________________________________ > GET INTERNET ACCESS FROM JUNO! > Juno offers FREE or PREMIUM Internet access for less! > Join Juno today! For your FREE software, visit: > http://dl.www.juno.com/get/web/. > > -- > 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 > > > > > > > > > ******************************************************************** > This email and any attachments are confidential to the intended > recipient and may also be privileged. If you are not the intended > recipient please delete it from your system and notify the sender. > You should not copy it or use it for any purpose nor disclose or > distribute its contents to any other person. > ******************************************************************** > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu