Sean, the device will be idle most of the time. The target application will be running ~19 days without recharging from a 12A/H 12V lead acid battery. Keep in mind that the battery has a self- discharge ratio that will leave me with ~80% of the charge (9.6 A/H). My ideal power supply should be extremely efficient in the <100 mA range. Due to the duty cycle (>1:60 for four days, >1:600 for 15 days), I can stand a *linear supply* performance for currents above 150 mA. I'm currently experimenting with a MAX1684 for the main circuit (<150 mA, 100 mA typical when full active) and a linear regulator (LM317) for the radiomodem (<5mA typical 98.3% of the time, 160~200mA average 1.6% of the time). I'm trying to trick the LM317 with large R1-R2 values (~8KÙ) to keep power consumption low. The radiomodem will work well from 3.3 to 4.5V, so I can bear a considerable deal of voltage shift in the regulation from this side. Though this may seem a nonsense, I'm actually getting better numbers at the end. Guille --- In lpc2000@yahoogroups.com, Sean <embeddedrelated@w...> wrote: > > Tom: > > I'm confused by your response. > > The datasheet clearly shows that it is possible, it even gives the the > schematic to do it. In effect you are building a switching regulator, the > same way that a premade one works, except with a much lower switching > frequency. > > I'd imagine that for high loads the efficiency isn't as good as a real > switching regulator (due to the lower switching frequency), but it is much > better than linear. I do not, however, know how well it performs with low > currents. > > Guillermo: > > What is the duty cycle going to be on your device? i.e. how much time will > it spend in idle mode vs low power vs full power mode? Perhaps asking the > question a different way: how much power (in watt-hours say) do you expect > to use between recharges? > > -- Sean > > At 01:16 AM 12/3/2005, Tom Walsh wrote: > >Sean wrote: > > > > >What type of efficiency does a linear regulator give you when setup in a > > >switching-style topology for low currents? > > > > > > > > > > >Figure about 30%, maybe %40, efficiency for a linear, three terminal > >regulator. It is not possible to use a Linear Regulator as a switched > >element... > > > > > >TomW > > > > > > > > >Check out L7805C datasheet figure 27 in case you don't know what I'm > > >talking about. > > > > > >While we're on offtopic, what diodes do you guys recommend using, > > >especially for lithium backup purposes? Most diodes that I see that are > > >frequently used have large forward voltage drops for any non- trivial > > >current draw. > > > > > >-- Sean > > > > > >At 12:50 PM 12/2/2005, Guillermo Prandi wrote: > > > > > > > > >>Thanks, Joel. Efficiency on those chips seems still very low (around > > >>50% for my circuit's average load, 15 mA), though the low quiescent > > >>current seems tempting. > > >> > > >>Guille > > >> > > >>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote: > > >> > > >> > > >>>Guille wrote, > > >>> > > >>> > > >>> > > >>>>Hi! I am in trouble trying to find a voltage regulator suitable > > >>>> > > >>>> > > >>for my > > >> > > >> > > >>>>project; my project features an LPC2138, a GPS and a radiomodem. > > >>>> > > >>>> > > >>When > > >> > > >> > > >>>>idle, it draws around 20-25 mA from the 3.3V source, 500 mA when > > >>>>working hard and with short (50 mS) peaks of up to 1.8A. The > > >>>> > > >>>> > > >>supply is > > >> > > >> > > >>>>a lead-acid 12V battery (can't change that), and occasionally, > > >>>> > > >>>> > > >>when the > > >> > > >> > > >>>>battery is charging, the input voltage will rise up to ~20V. The > > >>>>problem is the regulator efficiency. We were going for the LM2676- > > >>>> > > >>>> > > >>3.3V > > >> > > >> > > >>>>switching regulator, because it seemed simple and in range, but > > >>>> > > >>>> > > >>two > > >> > > >> > > >>>>things made it a poor choice: it draws about 4.3 mA from the > > >>>> > > >>>> > > >>battery > > >> > > >> > > >>>>just for its own supply, and its efficiency when the load is in > > >>>> > > >>>> > > >>the 20- > > >> > > >> > > >>>>25 mA range is awful (less than 50%, not counting Iquiescent). I > > >>>> > > >>>> > > >>looked > > >> > > >> > > >>>>everywhere but I couldn't find any other switcher with better > > >>>>performance in these conditions (12V in, 3.3V out, 20-25 mA > > >>>> > > >>>> > > >>average > > >> > > >> > > >>>>load, but >1.5A capability). And there's a catch! The radiomodem > > >>>> > > >>>> > > >>is > > >> > > >> > > >>>>extremely sensitive to VCC getting lower than 3.3V especially in > > >>>> > > >>>> > > >>the > > >> > > >> > > >>>>current peaks! Also, it should be relatively easy to find in ~400 > > >>>>quantities (i.e., Digikey, Mouser or your suggestion). > > >>>> > > >>>> > > >>>I've used the MAX5035 for automotive apps. Nice part. > > >>><<http://www.maxim->http://www.maxim->http://www.maxim- > > >>> > > >>> > > >>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0 > > >> > > >> > > >>>You might consider the MAX5090, it goes up to 2A. The input > > >>> > > >>> > > >>voltage range > > >> > > >> > > >>>is 6.5V to 72V. > > >>> > > >>>Joel > > >>> > > >>> > > >>> > > >> > > >> > > >> > > >> > > >> > > >>SPONSORED LINKS > > >><<http://groups.yahoo.com/gads? t=ms&k=Microprocessor&w1=Microprocessor&w > > 2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4& s=93&.sig=tsVC-J9hJ5qyXg0WPR0l6g>http://groups.yahoo.com/gads? t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+mic rocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC- J9hJ5qyXg0WPR0l6g>Microprocessor > > > > >><<http://groups.yahoo.com/gads? t=ms&k=Microcontrollers&w1=Microprocessor > > &w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c= 4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>http://groups.yahoo.com/gads? t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+m icrocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq0 1nxwg>Microcontrollers > > > > >><<http://groups.yahoo.com/gads? t=ms&k=Pic+microcontrollers&w1=Microproce > > ssor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocesso r&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>http://groups.yahoo.com/gads? t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=P ic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c 6LyBvUqVQ>Pic > > > > >>microcontrollers > > >><<http://groups.yahoo.com/gads? t=ms&k=8051+microprocessor&w1=Microproces > > sor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor &c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>http://groups.yahoo.com/gads? t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pi c+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVI lekkDP-A>8051 > > > > >>microprocessor > > >> > > >> > > >>---------- > > >>YAHOO! GROUPS LINKS > > >> > > >> * Visit your group > > "<<http://groups.yahoo.com/group/lpc2000>http://groups.yahoo.com/gro up/lpc2000>lpc2000" > > > > >>on the web. > > >> * > > >> * To unsubscribe from this group, send an email to: > > >> * > > >><mailto:lpc2000-unsubscribe@yahoogroups.com? subject=Unsubscribe>lpc2000- > > unsubscribe@yahoogroups.com > > >> > > >> * > > >> * Your use of Yahoo! Groups is subject to the > > >><<http://docs.yahoo.com/info/terms/>http://docs.yahoo.com/info/terms />Ya > > hoo! Terms of Service. > > >> > > >> > > >>---------- > > >> > > >> > > > > > > > > > > > > > > > > > >Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >-- > >Tom Walsh - WN3L - Embedded Systems Consultant > ><http://openhardware.net,>http://openhardware.net, http://cyberiansoftware.com > >"Windows? No thanks, I have work to do..." > >---------------------------------------------------- > > > > > > > > > >SPONSORED LINKS > ><http://groups.yahoo.com/gads? t=ms&k=Microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+mic rocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=tsVC- J9hJ5qyXg0WPR0l6g>Microprocessor > ><http://groups.yahoo.com/gads? t=ms&k=Microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+m icrocontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq0 1nxwg>Microcontrollers > ><http://groups.yahoo.com/gads? t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=P ic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c 6LyBvUqVQ>Pic > >microcontrollers > ><http://groups.yahoo.com/gads? t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pi c+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVI lekkDP-A>8051 > >microprocessor > > > > > >---------- > >YAHOO! 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Message
Re: Offtopic: any high efficiency voltage regulator suggestion?
2005-12-03 by Guillermo Prandi