Sean 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. > > > Read the schematic, it is a "trick". They are using the L78xx as a control element to govern the pulse width of the 2N3789 pass transistor. The PNP transistor is being used as the switch element. When the voltage across the 2000ufd cap drops below the L78xx output voltage, the L78xx begins to draw current at its' input, thus causing the 2N3789 to go into saturation, which in turn dumps current into the inductor. No, the app sheet just shows you a goofy switching regulator. It _is not_ an L78xx switching regulator. I would not expect efficiencies above the 70% range with a bipolar switch element (Vce drop causes heat loss). TomW >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+microcontrollers&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+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=DvJVNqC_pqRTm8Xq01nxwg>Microcontrollers >> >> >> >>>><<http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microproce >>>> >>>> >>ssor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>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=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 >> >> >> >>>>microprocessor >>>> >>>> >>>>---------- >>>>YAHOO! GROUPS LINKS >>>> >>>> * Visit your group >>>> >>>> >>"<<http://groups.yahoo.com/group/lpc2000>http://groups.yahoo.com/group/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+microcontrollers&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>Microcontrollers >><http://groups.yahoo.com/gads?t=ms&k=Pic+microcontrollers&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=TpkoX4KofDJ7c6LyBvUqVQ>Pic >>microcontrollers >><http://groups.yahoo.com/gads?t=ms&k=8051+microprocessor&w1=Microprocessor&w2=Microcontrollers&w3=Pic+microcontrollers&w4=8051+microprocessor&c=4&s=93&.sig=1Ipf1Fjfbd_HVIlekkDP-A>8051 >>microprocessor >> >> >>---------- >>YAHOO! GROUPS LINKS >> >> * Visit your group "<http://groups.yahoo.com/group/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/>Yahoo! Terms of Service. >> >> >>---------- >> >> > > > > > >Yahoo! Groups Links > > > > > > > > > -- Tom Walsh - WN3L - Embedded Systems Consultant http://openhardware.net, http://cyberiansoftware.com "Windows? No thanks, I have work to do..." ----------------------------------------------------
Message
Re: [lpc2000] Re: Offtopic: any high efficiency voltage regulator suggestion?
2005-12-03 by Tom Walsh