Favorite reverse bias protection for battery circuits
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From: Hammy on 16 Mar 2010 15:28 On Tue, 16 Mar 2010 11:18:10 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Hammy wrote: >> On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> >> wrote: >> >>> Hi All, >>> Still working on my color reader, and getting close. Biggest problem >>> is that now I have almost TOO much drive on my LEDs, but that I can >>> deal with! >>> >>> Now, to the latest problem. My system is for the visually impaired. I >>> just put the batteries in one of my prototypes backwards, and it >>> didn't last very long. While I expect this device to have very long >>> battery life, since it normally doesn't operate but for a second or >>> two, it looks like the MC1253's don't like getting reversed biased >>> very long. So, for my design question of the day - What is your >>> favorite circuit for preventing reverse bias from the batteries? The >>> old diode trick drops too much voltage, so wondered if there are any >>> clever FET tricks to block backwards voltages. >>> >>> Thanks! >>> >>> Charlie >> I usually use #2 on this page a shorting shottky. >> >> http://www.recom-international.com/press/Reverse%20Polarity%20Protection%20for%20DC/DC%20Converters.html > > >That renders the unit dead and a blind or almost blind person will have >a hard time finding or buying the proper fuse and installing it. Thats what they have seeing eye dogs for:-) Jokeing. Of course your right for a blind person either #3 or a keyed battery connection. With a brail instruction manual >Charlie: Solution #3 is the ticket (look on Hammy's link). But make sure >that the FET is guaranteed to be fully turned on at the lowest allowed >battery voltage, IOW the point where an UVLO comes on.
From: Joerg on 16 Mar 2010 15:39 Jim Thompson wrote: > On Tue, 16 Mar 2010 11:46:11 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> >>> wrote: >>> >>>> Hi All, >>>> Still working on my color reader, and getting close. Biggest problem >>>> is that now I have almost TOO much drive on my LEDs, but that I can >>>> deal with! >>>> >>>> Now, to the latest problem. My system is for the visually impaired. I >>>> just put the batteries in one of my prototypes backwards, and it >>>> didn't last very long. While I expect this device to have very long >>>> battery life, since it normally doesn't operate but for a second or >>>> two, it looks like the MC1253's don't like getting reversed biased >>>> very long. So, for my design question of the day - What is your >>>> favorite circuit for preventing reverse bias from the batteries? The >>>> old diode trick drops too much voltage, so wondered if there are any >>>> clever FET tricks to block backwards voltages. >>>> >>>> Thanks! >>>> >>>> Charlie >>> Some variation on this... >>> >>> http://analog-innovations.com/SED/PerfectDiodeForChargerIsolation.pdf >>> >>> Do you have enough voltage to turn on MOSFET's? >>> >>> Probably could do it with bipolar's... I'll ponder :-) >>> >> Which HV CMOS process did that get rolled onto, if I may ask? > > California Micro Devices (do they still exist?) for a LiIon > charge/discharge controller. > Swallowed by ON, just like AMI was :-( -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 16 Mar 2010 15:42 Hammy wrote: > On Tue, 16 Mar 2010 11:18:10 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Hammy wrote: >>> On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmondson(a)ieee.org> >>> wrote: >>> >>>> Hi All, >>>> Still working on my color reader, and getting close. Biggest problem >>>> is that now I have almost TOO much drive on my LEDs, but that I can >>>> deal with! >>>> >>>> Now, to the latest problem. My system is for the visually impaired. I >>>> just put the batteries in one of my prototypes backwards, and it >>>> didn't last very long. While I expect this device to have very long >>>> battery life, since it normally doesn't operate but for a second or >>>> two, it looks like the MC1253's don't like getting reversed biased >>>> very long. So, for my design question of the day - What is your >>>> favorite circuit for preventing reverse bias from the batteries? The >>>> old diode trick drops too much voltage, so wondered if there are any >>>> clever FET tricks to block backwards voltages. >>>> >>>> Thanks! >>>> >>>> Charlie >>> I usually use #2 on this page a shorting shottky. >>> >>> http://www.recom-international.com/press/Reverse%20Polarity%20Protection%20for%20DC/DC%20Converters.html >> >> That renders the unit dead and a blind or almost blind person will have >> a hard time finding or buying the proper fuse and installing it. > Thats what they have seeing eye dogs for:-) Jokeing. > Ok, I'll ask our new Labrador when she is back :-) She went through the first three phases of guide dog training and then had to be discharged for a medical condition (soft trachea, happens a lot with guide dog Labs). > Of course your right for a blind person either #3 or a keyed battery > connection. With a brail instruction manual > It's actually even better these days. A nearly blind relative has a Casio watch that talks. >> Charlie: Solution #3 is the ticket (look on Hammy's link). But make sure >> that the FET is guaranteed to be fully turned on at the lowest allowed >> battery voltage, IOW the point where an UVLO comes on. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Charlie E. on 16 Mar 2010 15:43 On Tue, 16 Mar 2010 12:15:25 -0700, D Yuniskis <not.going.to.be(a)seen.com> wrote: >Hi Charlie, > >Charlie E. wrote: >> Still working on my color reader, and getting close. Biggest problem >> is that now I have almost TOO much drive on my LEDs, but that I can >> deal with! >> >> Now, to the latest problem. My system is for the visually impaired. I >> just put the batteries in one of my prototypes backwards, and it >> didn't last very long. While I expect this device to have very long >> battery life, since it normally doesn't operate but for a second or >> two, it looks like the MC1253's don't like getting reversed biased >> very long. So, for my design question of the day - What is your >> favorite circuit for preventing reverse bias from the batteries? The >> old diode trick drops too much voltage, so wondered if there are any >> clever FET tricks to block backwards voltages. > >Solve this problem *mechanically*. You need to prevent the >batteries from being *installed* wrong, in the first place. >E.g., any sort of circuit that protects (the rest of) the >circuit from reversed battery won't do anything to tell the >VI user *why* your device isn't working. Are the batteries >*dead*? Installed wrong? Corroded terminals? Or is the >*device* broken?? > >"Key" the battery holder so the user can feel the correct >orientation for the batteries *and* so it prevents the >cells from making electrical contact if not oriented >properly. > >Think of how the *user* is going to interact with your device. >Close your eyes and "figure out" why it doesn't work :-/ Would be the best result, but these are standard AA cells, no way to key them without using expensive custom battery packs. Not the way to go for inexpensive... Will be looking for a good PMOS FET that will still conduct with two low AA batteries, probably around 1.8VDC, if they make one! ;-) Thanks All! Charlie
From: D Yuniskis on 16 Mar 2010 16:03
Hi Charlie, Charlie E. wrote: > On Tue, 16 Mar 2010 12:15:25 -0700, D Yuniskis > <not.going.to.be(a)seen.com> wrote: > >>> Now, to the latest problem. My system is for the visually impaired. I >>> just put the batteries in one of my prototypes backwards, and it >>> didn't last very long. While I expect this device to have very long >>> battery life, since it normally doesn't operate but for a second or >>> two, it looks like the MC1253's don't like getting reversed biased >>> very long. So, for my design question of the day - What is your >>> favorite circuit for preventing reverse bias from the batteries? The >>> old diode trick drops too much voltage, so wondered if there are any >>> clever FET tricks to block backwards voltages. >> Solve this problem *mechanically*. You need to prevent the >> batteries from being *installed* wrong, in the first place. >> E.g., any sort of circuit that protects (the rest of) the >> circuit from reversed battery won't do anything to tell the >> VI user *why* your device isn't working. Are the batteries >> *dead*? Installed wrong? Corroded terminals? Or is the >> *device* broken?? >> >> "Key" the battery holder so the user can feel the correct >> orientation for the batteries *and* so it prevents the >> cells from making electrical contact if not oriented >> properly. >> >> Think of how the *user* is going to interact with your device. >> Close your eyes and "figure out" why it doesn't work :-/ > > Would be the best result, but these are standard AA cells, no way to > key them without using expensive custom battery packs. Not the way to > go for inexpensive... I take it you aren't making a custom (molded) case? Why not purchase COTS battery holder that *is* "keyed"? > Will be looking for a good PMOS FET that will still conduct with two > low AA batteries, probably around 1.8VDC, if they make one! ;-) If you go that route, consider how your design can tell the user "yes, I am working" vs. absence of that indication so the user can deduce "something is wrong with the batteries or their installation" (or the device) |