Post by thread:Polarity inversion protection

How about putting a diode (or more) reversed bias parallel to the power source. If the polarity IS reversed, you will only get a negative voltage equal to the forward voltage drop of the diode. This will work as long at the current doesn't kill the diode, so don't try using with a lead-acid battery application! If you know your supply current , you can use a current limit resistor. Use R=(Vsource-Vdiode)/Imax diode. You can then double check to ensure the supply voltage will not drop too much. Good luck Current Limiting (Vs)---------/\/\/\/---------------------> To device | _ Diode ^ 1N4005 | ----------------------------------> Gnd TAS ----------------------------------------------------------------- Sent from the desk of: Terry Allen Steen, EE spam_OUTengineeringTakeThisOuTmarinapower.com 332 McLaws Circle, Ste 111 757-258-8800 (Voice) Williamsburg, Va 23185 757-258-8805 (FAX) ----------------------------------------------------------------- !I AM A WHALE MAIL USER! If you have a large file to send, goto http://www.whalemail.com send them to: mplengineer Give me your account and I will use it also ----------------------------------------------------------------- Visit our web-site: http://www.marinapower.com -----------------------------------------------------------------

On Mon, 08 Nov 1999, you wrote: > Hello List, > > I have realized an alarm for my bycicle using a 12C508. It is powered by two A A > size alkaline battery. > > I would like to know if there is a simple (and economic!!) solution which > I can use to protect my circuit against polarity inversion during battery chan ge. > (I know it's a remote possibility, but it exists) > > I thought to use a serie diode, but the voltage drop bring the PIC power volta ge > near the power supply limit of the MCU. > I can't think of it right now, but there is an arrangement using a single MOSFET which will provide this. Possibly the gate is connected to the drain, possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz and Hill. It's a very simple circuit, but as I said, I can't think of it now (such is the effect of a few beers..). Play around with this, and see what you can come up with. I'll try again in the morning. Jason Langenauer Mechanical and Space Enginnering, The University of Queensland -- Lady Astor: If you were my husband, I'd poison you drink. Winston Churchill : If I was your husband, I'd drink it.

Yes, it is a diode connected mosfet. TAS At 10:03 AM 11/9/99 +1000, you wrote: >On Mon, 08 Nov 1999, you wrote: >> Hello List, >> >> I have realized an alarm for my bycicle using a 12C508. It is powered by two AA >> size alkaline battery. >> >> I would like to know if there is a simple (and economic!!) solution which >> I can use to protect my circuit against polarity inversion during battery change. >> (I know it's a remote possibility, but it exists) >> >> I thought to use a serie diode, but the voltage drop bring the PIC power voltage >> near the power supply limit of the MCU. >> >I can't think of it right now, but there is an arrangement using a single >MOSFET which will provide this. Possibly the gate is connected to the drain, >possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz and >Hill. It's a very simple circuit, but as I said, I can't think of it now (such >is the effect of a few beers..). Play around with this, and see what you can >come up with. I'll try again in the morning. > >Jason Langenauer >Mechanical and Space Enginnering, The University of Queensland >-- >Lady Astor: If you were my husband, I'd poison you drink. >Winston Churchill : If I was your husband, I'd drink it. > > ----------------------------------------------------------------- Sent from the desk of: Terry Allen Steen, EE .....engineeringKILLspam@spam@marinapower.com 332 McLaws Circle, Ste 111 757-258-8800 (Voice) Williamsburg, Va 23185 757-258-8805 (FAX) ----------------------------------------------------------------- !I AM A WHALE MAIL USER! If you have a large file to send, goto http://www.whalemail.com send them to: mplengineer Give me your account and I will use it also ----------------------------------------------------------------- Visit our web-site: http://www.marinapower.com -----------------------------------------------------------------

Ok, use a reversed diode to the PIC with a low value resistor in series to the cells. It means, that if reversing cells polarity it will be drained by the resistor+diode. In real you would be short circuiting the cells, but not in a dangerous current (limited by the resistor). Calculate the resistor to drop only 50mV on normal operation, but when cells are inverted it will dissipate heat, leaving only the diode voltage drop to the PIC. For example, if the normal operation current is around 10mA, the resistor should be 50mV/10mA = 5 Ohms. If cells are assembled reversed, the diode will conduct directly over the resistor, so it will be 3V-0.6V(diode) / 5 Ohms = 480mA, enough to keep the reversed voltage over the PIC at 0.6V without exploding the cells. For better protection, you could use a Schottky diode or even an "old germanium diode" that drops only 0.2Vdc. If your circuit drain pulses of high current, bigger than 10mA, you can add an electrolytic capacitor in parallel to the 5 Ohms diode, as a bypass to those high surge periods. For sure, if you can afford to reduce 0.2Vdc from the PIC, install only the germanium diode in series with the cells... :) Wagner. Jason Langenauer wrote: > > On Mon, 08 Nov 1999, you wrote: > > Hello List, > > > > I have realized an alarm for my bycicle using a 12C508. It is powered by two AA > > size alkaline battery. > > > > I would like to know if there is a simple (and economic!!) solution which > > I can use to protect my circuit against polarity inversion during battery ch ange. > > (I know it's a remote possibility, but it exists) > > > > I thought to use a serie diode, but the voltage drop bring the PIC power vol tage {Quote hidden}> > near the power supply limit of the MCU. > > > I can't think of it right now, but there is an arrangement using a single > MOSFET which will provide this. Possibly the gate is connected to the drain, > possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz an d > Hill. It's a very simple circuit, but as I said, I can't think of it now (such > is the effect of a few beers..). Play around with this, and see what you can > come up with. I'll try again in the morning. > > Jason Langenauer > Mechanical and Space Enginnering, The University of Queensland > -- > Lady Astor: If you were my husband, I'd poison you drink. > Winston Churchill : If I was your husband, I'd drink it.

Terry, You can take an enhancement power MOSFET and put in the negative return line from your circuit. The gate is driven through a 1 Meg resistor from the positive battery terminal. A correct power connection drives the MOSFET fully ON, and everything works. Reversing the supply connections turns the MOSFET OFF, and no current flows and you're protected. Correct the power connections, and you're back to normal. There is very little voltage drop across the MOSFET. Select a MOSFET with a low "R(on)" resistance, and there will be very little voltage drop. You may also require a 5 volt logic mosfet, which will turn on around 2 volts. The diode approach is probably the best rather than the above if it is for an inexpensive project. David <Hello List, < <I have realized an alarm for my bycicle using a 12C508. It is powered by two AA <size alkaline battery. < <I would like to know if there is a simple (and economic!!) solution which <I can use to protect my circuit against polarity inversion during battery change. <(I know it's a remote possibility, but it exists) < <I thought to use a serie diode, but the voltage drop bring the PIC power voltage <near the power supply limit of the MCU. < Thanks. < < <Best regards, <Michele

How about a series PTC then a shunt diode. The diode will conduct if the batteries are put in backwards, opening the PTC. Harold On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele <mazzoniKILLspamTECHEMAIL.COM> writes: {Quote hidden}>Hello List, > >I have realized an alarm for my bycicle using a 12C508. It is powered >by two AA >size alkaline battery. > >I would like to know if there is a simple (and economic!!) solution >which >I can use to protect my circuit against polarity inversion during >battery change. >(I know it's a remote possibility, but it exists) > >I thought to use a serie diode, but the voltage drop bring the PIC >power voltage >near the power supply limit of the MCU. > >Thanks. > > >Best regards, >Michele > >_______________________________________________________ >Are you a Techie? Get Your Free Tech Email Address Now! >Many to choose from! Visit http://www.TechEmail.com ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: dl.http://www.juno.com/dynoget/tagj.

Harold's suggestion is good, but it can be improved by using an appropriate valued zener for the diode ... also gives overvoltage protection. It's saved my breadboard circuits from frying more than once. - Nick - Harold Hallikainen wrote: {Quote hidden}> > How about a series PTC then a shunt diode. The diode will conduct if > the batteries are put in backwards, opening the PTC. > > Harold > > On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele <.....mazzoniKILLspam.....TECHEMAIL.COM> > writes: > >Hello List, > > > >I have realized an alarm for my bycicle using a 12C508. It is powered > >by two AA > >size alkaline battery. > > > >I would like to know if there is a simple (and economic!!) solution > >which > >I can use to protect my circuit against polarity inversion during > >battery change. > >(I know it's a remote possibility, but it exists) > > > >I thought to use a serie diode, but the voltage drop bring the PIC > >power voltage > >near the power supply limit of the MCU. > > > >Thanks. > > > > > >Best regards, > >Michele > > > >_______________________________________________________ > >Are you a Techie? Get Your Free Tech Email Address Now! > >Many to choose from! Visit http://www.TechEmail.com > > ___________________________________________________________________ > Get the Internet just the way you want it. > Free software, free e-mail, and free Internet access for a month! > Try Juno Web: dl.http://www.juno.com/dynoget/tagj.

> I thought to use a serie diode, but the voltage drop bring the PIC power volta ge > near the power supply limit of the MCU. I've just been through this exercise for a similar circuit to protect against the batteries being put in backwards. Initially I used a Zetex ZVP4424A low Vgs, P-channel, enhancement mode FET. Just tie the Gate to your negative terminal. When the circuit is connected backwards, the FET is biased off and the Drain/Source diode is reverse biased. When it is the right way around, the diode is forward biased and gets shunted by the FET turning on when the voltage starts to pass the Vgs threshold. Eventually I changed this to just a schottky diode because all of the loads could cope with reverse connection (eg. LEDs, dc motor switched by transistor, etc) and I could put those on the battery side of the diode. That just left the PIC drawing about 25uA which puts the voltage drop well down on the curve so the diode is only costing around < 0.15V. You have to look carefully at your circuit and calculate what will happen at power up (reset time vs. circuit capacitance). The diode is cheaper but it comes with trade-offs. The FET is simple and works well. It just costs a bit more (which wasn't acceptable for my case). One thing that caught me was that the 16C54 and 16C54A (LP) are spec'd down to 2.5V but the later revisions (B & C) are only spec'd (and operate) down to 3V.This is the opposite to what I thought was the effect of a die shrink (ie. specs stay the same or get better) but the Microchip man at ESC had a plausable explanation so I'm better educated now. Watch out for die shrunk parts. Steve. ====================================================== Steve Baldwin Electronic Product Design TLA Microsystems Ltd Microcontroller Specialists PO Box 15-680, New Lynn http://www.tla.co.nz Auckland, New Zealand ph +64 9 820-2221 email: EraseMEstevebspam_OUTTakeThisOuTtla.co.nz fax +64 9 820-1929 ======================================================

Yes, an even better idea! I had not thought of that for this application, but it sounds good. In the products I've done, I don't know how someone could stuff more AA cells in there than I had designed for, but SOMEONE could overvoltage it! Harold Harold Hallikainen haroldspam_OUThallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm On Mon, 8 Nov 1999 08:14:03 -0800 Nick Taylor <@spam@ntaylorKILLspamINAME.COM> writes: {Quote hidden}>Harold's suggestion is good, but it can be improved by using an >appropriate valued zener for the diode ... also gives overvoltage >protection. It's saved my breadboard circuits from frying more >than once. > - Nick - > >Harold Hallikainen wrote: >> >> How about a series PTC then a shunt diode. The diode will >conduct if >> the batteries are put in backwards, opening the PTC. >> >> Harold >> >> On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele ><KILLspammazzoniKILLspamTECHEMAIL.COM> >> writes: >> >Hello List, >> > >> >I have realized an alarm for my bycicle using a 12C508. It is >powered >> >by two AA >> >size alkaline battery. >> > >> >I would like to know if there is a simple (and economic!!) solution >> >which >> >I can use to protect my circuit against polarity inversion during >> >battery change. >> >(I know it's a remote possibility, but it exists) >> > >> >I thought to use a serie diode, but the voltage drop bring the PIC >> >power voltage >> >near the power supply limit of the MCU. >> > >> >Thanks. >> > >> > >> >Best regards, >> >Michele >> > >> >_______________________________________________________ >> >Are you a Techie? Get Your Free Tech Email Address Now! >> >Many to choose from! Visit http://www.TechEmail.com >> >> ___________________________________________________________________ >> Get the Internet just the way you want it. >> Free software, free e-mail, and free Internet access for a month! >> Try Juno Web: dl.http://www.juno.com/dynoget/tagj. ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: dl.http://www.juno.com/dynoget/tagj.

Easy; Someone writes up a "How to run this off an AC to DC adapter, by adding a power socket" web page, then someone who doesn't know what they're doing sticks a 48VDC 300 mA power lump into that socket, blowing things up if not protected. (I've seen this done, sadly; Also quite often just "any handy power lump that fits" is assumed to work just fine, a Zener is a GOOD idea, so's the FET.) An idea on this: How about a Unidirectional TVS (Transient Voltage Suppressor) instead of a Zener? They're fast, cheap, and have pretty high peak power ratings; I am not sure what their average power ratings are, which is why I'll ask if anyone knows what average power rating a 600W TVS will handle - anyone? I can just cook one to destruction, I suppose <G> (Also: I need the spice models for these, both uni- and bi-directionals; if anyone has those handy, it'd be nice! Off-list, of course <G>) Mark (about 1/2 here today.) Harold M Hallikainen wrote: {Quote hidden}> > Yes, an even better idea! I had not thought of that for this > application, but it sounds good. In the products I've done, I don't know > how someone could stuff more AA cells in there than I had designed for, > but SOMEONE could overvoltage it! > > Harold > > Harold Hallikainen > RemoveMEharoldTakeThisOuThallikainen.com > Hallikainen & Friends, Inc. > See the FCC Rules at http://hallikainen.com/FccRules and comments filed > in LPFM proceeding at http://hallikainen.com/lpfm > > On Mon, 8 Nov 1999 08:14:03 -0800 Nick Taylor <spamBeGonentaylorspamBeGoneINAME.COM> writes: > >Harold's suggestion is good, but it can be improved by using an > >appropriate valued zener for the diode ... also gives overvoltage > >protection. It's saved my breadboard circuits from frying more > >than once. > > - Nick - > > > >Harold Hallikainen wrote: > >> > >> How about a series PTC then a shunt diode. The diode will > >conduct if > >> the batteries are put in backwards, opening the PTC. > >> > >> Harold > >> > >> On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele > ><TakeThisOuTmazzoniEraseMEspam_OUTTECHEMAIL.COM> > >> writes: > >> >Hello List, > >> > > >> >I have realized an alarm for my bycicle using a 12C508. It is > >powered > >> >by two AA > >> >size alkaline battery. > >> > > >> >I would like to know if there is a simple (and economic!!) solution > >> >which > >> >I can use to protect my circuit against polarity inversion during > >> >battery change. > >> >(I know it's a remote possibility, but it exists) > >> > > >> >I thought to use a serie diode, but the voltage drop bring the PIC > >> >power voltage > >> >near the power supply limit of the MCU. > >> > > >> >Thanks. > >> > > >> > > >> >Best regards, > >> >Michele > >> > > >> >_______________________________________________________ > >> >Are you a Techie? Get Your Free Tech Email Address Now! > >> >Many to choose from! Visit http://www.TechEmail.com > >> > >> ___________________________________________________________________ > >> Get the Internet just the way you want it. > >> Free software, free e-mail, and free Internet access for a month! > >> Try Juno Web: dl.http://www.juno.com/dynoget/tagj. > > ___________________________________________________________________ > Get the Internet just the way you want it. > Free software, free e-mail, and free Internet access for a month! > Try Juno Web: dl.http://www.juno.com/dynoget/tagj. -- I do small package shipping for small businesses, world-wide.

Hi, I would use a serial connected Schottky. Regards, Imre On Mon, 8 Nov 1999, Wagner Lipnharski wrote: {Quote hidden}> Ok, use a reversed diode to the PIC with a low value resistor in series > to the cells. It means, that if reversing cells polarity it will be > drained by the resistor+diode. In real you would be short circuiting the > cells, but not in a dangerous current (limited by the resistor). > Calculate the resistor to drop only 50mV on normal operation, but when > cells are inverted it will dissipate heat, leaving only the diode > voltage drop to the PIC. > > For example, if the normal operation current is around 10mA, the > resistor should be 50mV/10mA = 5 Ohms. If cells are assembled reversed, > the diode will conduct directly over the resistor, so it will be > 3V-0.6V(diode) / 5 Ohms = 480mA, enough to keep the reversed voltage > over the PIC at 0.6V without exploding the cells. > > For better protection, you could use a Schottky diode or even an "old > germanium diode" that drops only 0.2Vdc. > If your circuit drain pulses of high current, bigger than 10mA, you can > add an electrolytic capacitor in parallel to the 5 Ohms diode, as a > bypass to those high surge periods. > > For sure, if you can afford to reduce 0.2Vdc from the PIC, install only > the germanium diode in series with the cells... :) > > Wagner. > > > > > Jason Langenauer wrote: > > > > On Mon, 08 Nov 1999, you wrote: > > > Hello List, > > > > > > I have realized an alarm for my bycicle using a 12C508. It is powered by t wo AA > > > size alkaline battery. > > > > > > I would like to know if there is a simple (and economic!!) solution which > > > I can use to protect my circuit against polarity inversion during battery change. > > > (I know it's a remote possibility, but it exists) > > > > > > I thought to use a serie diode, but the voltage drop bring the PIC power v oltage > > > near the power supply limit of the MCU. > > > > > I can't think of it right now, but there is an arrangement using a single > > MOSFET which will provide this. Possibly the gate is connected to the drain, > > possibly it is an N-channel MOSFET, and possibly the circuit is in Horowitz and > > Hill. It's a very simple circuit, but as I said, I can't think of it now (su ch {Quote hidden}> > is the effect of a few beers..). Play around with this, and see what you can > > come up with. I'll try again in the morning. > > > > Jason Langenauer > > Mechanical and Space Enginnering, The University of Queensland > > -- > > Lady Astor: If you were my husband, I'd poison you drink. > > Winston Churchill : If I was your husband, I'd drink it. > >

<x-flowed>If the battery holder is of the tube type with a spring in the bottom and a flat piece of metal on the top then you can cut a circle the size of the battery from a piece of tape. Make a hole so the + pole on the battery can make contact. Then stick it on the + connector of the battery holder. Best regards, Hekan {Quote hidden}>From: mazzoni michele <RemoveMEmazzoniTakeThisOuTTECHEMAIL.COM> >Reply-To: pic microcontroller discussion list <PICLISTEraseME.....MITVMA.MIT.EDU> >To: EraseMEPICLISTMITVMA.MIT.EDU >Subject: Polarity inversion protection >Date: Mon, 8 Nov 1999 05:26:07 -0800 > >Hello List, > >I have realized an alarm for my bycicle using a 12C508. It is powered by >two AA >size alkaline battery. > >I would like to know if there is a simple (and economic!!) solution which >I can use to protect my circuit against polarity inversion during battery >change. >(I know it's a remote possibility, but it exists) > >I thought to use a serie diode, but the voltage drop bring the PIC power >voltage >near the power supply limit of the MCU. > >Thanks. > > >Best regards, >Michele > >_______________________________________________________ >Are you a Techie? Get Your Free Tech Email Address Now! >Many to choose from! Visit http://www.TechEmail.com ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com </x-flowed>