Thanks for pointing out the National line and in particular the LM2671. That gives me a quick, easy, and reasonably inexpensive option for first hardware iteration. And, more importantly, I am learning a lot:) --BobG -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Dave Dilatush Sent: Sunday, July 22, 2001 10:10 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [OT]: How to reduce power consumption for battery operated circuits? BobG wrote... >>>Hope this helps... > >Wow, it sure does. Thanks for detailed explanation. You're welcome; glad I could be of some help. >Here is another, related question: I have two enclosures making up my >device - one powering the other through a cable that also carries serial >Tx/Rx. The first is powered from a wall transformer. Can I supply >regulated 5V to the remote device (6-12 ft), or am I better off sending the >higher, unregulated voltage to the remote device and give it its own, second >5v reg? The remote unit draws 50ma typical, 120ma in surges. Hmmm... Depends on the size of the wire, and how tightly you need the 5 volt supply to be regulated at the end of the 6-12 feet of cable. If you have any analog stuff out there in the remote unit that needs an accurate supply voltage, sending 12 volts to the remote and then regulating it down to 5 volts locally might be the best choice. Otherwise, if there's only digital stuff out there, I think I might be tempted to just ship the 5V down the cable (with a generous bypass capacitor at the receiving end). >Details of what I am doing if you are curious: > >Wall Transformer: Main Enclosure: LCD Enclosure: >12V unregulated: -> --------12V-----> > 5V@250ma 5V@100ma > 3V@40ma -12V@2ma > >My breadboarded prototype (which works) uses a 12v unregulated wall >transformer and I have lots of regulators around. The 12v wall wart >connects to the main enclosure where a 5V linear reg supplies about 250ma. >This enclosure also has a 3V linear reg that drops the 5V down for about >50ma at 3v. >A twisted pair cable takes the +12V unregulated and serial signals to the >second enclosure that is basically a serial LCD. In fact the prototype uses >a serial LCD I bought from www.earchLCD.com. It's a nice product, but too >expensive for this project and with a lot of extra features I am not using. >This serial LCD board has another 5v linear reg to supply the logic (100ma) >and an LTC1044A converts the +12 to -12V for the 2ma Vee for the LCD. Since >I am making a new, leaner serial LCD board from scratch, I figured might be >able to reduce the components. > >Also, the more important thing I am trying to solve with changing the power >supply method is the heat generated by the 5V linear reg in the main >circuit. It has well over 7 volts of head voltage @ 1/4 amp, so it tends to >get hot. I want to put it in an enclosure without a fan. Now, that might be a candidate for a switching regulator: you've got a modest amount of power there, and a heat problem you want to solve. Check out National Semiconductor's LM2671, which is rated at a half-ampere. That might do the trick; it will certainly run cool, as they project about 92% efficiency for operation at 12V in/5V out at 500 mA. >So, I figured that I could use a 5V transformer (over-rated so the reg sees >at at least 5+(its drop out) at full load) and use only one 5v reg in the >main enclosure. I could send the regulated 5V over the serial connection to >power so that the display enclosure's would not need another. Then at the >display enclosure boost and invert the +5v to -12v. The -12V really needs >to be set between -10V and -8V to adjust the contrast for a particular LCD. >The data sheet for the LCD suggests a simple voltage divider with a pot >since the current is so small. I am thinking of putting in a variable reg >so that the adustment will be more stable for the end user. You might not need a regulator; but you could always design one in, and bypass it if it proves unnecessary. Regards, Dave -- 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