Post by thread:[EE]: Regulator shorting?

I am working on a circuit that uses an Atmel AVR in a speed controller for an R/C airplane. The AVR and R/C receiver are powered by an LP2986IM 5 volt linear low dropout regulator. Once the battery gets down to 6 volts it's supposed to cut off the motor. When I tried it the motor stopped, the red light went on, and the regulator started smoking! It draws about 400 mA which is the short-circuit limit for the regulator. It gets very hot and I can't leave it on more than 1 or 2 seconds. Also the output voltage rises to 5.7 volts, which is (or close to) the input voltage (and enough to possibly wreck the AVR). The strange part is it's fine until the voltage drops under 6 V or so. (I raised the cutoff setting and it was fine). Does anyone have any idea what's wrong with this thing? Right now I'm afraid to test it too much; everything is SMT and I don't really want to build another one. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Is it possible the circuit is turning the motor on and off repeatedly? That could generate all sorts of mayhem, especially if you have no provision made for catching released energy from the motor. At the very least you should probably have a catch diode across the motor. Also you may need some bulk capacitance across the battery voltage. More description of the circuit or a snip of the schematic would help further diagnosis. Cheerful regards, Bob -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

I don't think that's the problem since it works fine as long as the battery stays above ~ 6 V. I can speed up and slow down the motor and turn it on and off and everything works fine. There is a diode going backwards across the motor and 3 capacitors, plus a 10 uF cap right next to the regulator. I also tried unplugging the motor as soon as it shut off but the regulator still started getting hot. There is another regulator on the board, an LM2940, which interestingly seems to be OK. I don't think anything hooked up to the 2986 is causing trouble - the AVR stays cool and the R/C receiver isn't bothering it. I will draw a schematic as soon as I finish downloading Eagle. Bob Blick wrote: {Quote hidden}> > Is it possible the circuit is turning the motor on and off repeatedly? > That could generate all sorts of mayhem, especially if you have no > provision made for catching released energy from the motor. At the very > least you should probably have a catch diode across the motor. Also you > may need some bulk capacitance across the battery voltage. > > More description of the circuit or a snip of the schematic would help > further diagnosis. > > Cheerful regards, > > Bob > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

part 0 44 bytes his is a multi-part message in MIME format. part 1 648 bytes content-type:text/plain; charset=us-ascii (decoded 7bit) Not the tidiest schematic I'm afraid... Eagle and I don't get along very well. The AVR (not shown) is connected to the 5 volt supply and has a couple of 0.1 uF capacitors. One ADC goes to the battery through a voltage divider (5.6K and 3.3K resistors plus a capacitor). It also has 2 LEDs, the PWM output to the MOSFET, and an interrupt input from the R/C receiver. There is also another regulator (an LM2940) but it's not connected to anything right now except a capacitor. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body part 2 18964 bytes content-type:image/gif; name="esc.gif" (decode) part 3 2 bytes -

On Friday 25 April 2003 03:13 pm, stanton54 wrote: > Not the tidiest schematic I'm afraid... Eagle and I don't get along > very well. > > The AVR (not shown) is connected to the 5 volt supply and has a > couple of 0.1 uF capacitors. One ADC goes to the battery through a > voltage divider (5.6K and 3.3K resistors plus a capacitor). It also > has 2 LEDs, the PWM output to the MOSFET, and an interrupt input > from the R/C receiver. > There is also another regulator (an LM2940) but it's not connected > to anything right now except a capacitor. Do you have a diode or snubber across the motor? -- Ned Konz http://bike-nomad.com GPG key ID: BEEA7EFE -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Check your circuit for the condition noted on the data sheet regarding the output voltage EVER getting higher than the input voltage. If this happens, a parasitic SCR gets turned on in the LP2986 and it will then get very hot. The data sheet tells how to avoid this. So even if you don't think that is the problem, try the schottky from Vin to Vout (cathode to Vin) as the datasheet suggests. Make sure to put it RIGHT on the regulator with shortest leads possible. Good luck! Tom M. At 06:13 PM 4/25/03 -0400, you wrote: {Quote hidden}>Not the tidiest schematic I'm afraid... Eagle and I don't get along >very well. > >The AVR (not shown) is connected to the 5 volt supply and has a couple >of 0.1 uF capacitors. One ADC goes to the battery through a voltage >divider (5.6K and 3.3K resistors plus a capacitor). It also has 2 LEDs, >the PWM output to the MOSFET, and an interrupt input from the R/C >receiver. >There is also another regulator (an LM2940) but it's not connected to >anything right now except a capacitor. > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

There is a 1N4004 and 3 capacitors, one between the terminals, and one from each terminal to the case. I checked and the diode is still OK (I did blow one up once; I tried to get away with using one that was too small). Ned Konz wrote: {Quote hidden}> > Do you have a diode or snubber across the motor? > > -- > Ned Konz > http://bike-nomad.com > GPG key ID: BEEA7EFE > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

Thanks for the suggestion, I will try this. Maybe all the big capacitors are causing the problem - the input drops down but the 5V line stays high for a bit, a little noise from the motor gets in the wrong spot, and zzzt! Tom Messenger wrote: {Quote hidden}> > Check your circuit for the condition noted on the data sheet regarding the > output voltage EVER getting higher than the input voltage. If this > happens, a parasitic SCR gets turned on in the LP2986 and it will then get > very hot. The data sheet tells how to avoid this. So even if you don't > think that is the problem, try the schottky from Vin to Vout (cathode to > Vin) as the datasheet suggests. Make sure to put it RIGHT on the regulator > with shortest leads possible. > > Good luck! > Tom M. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Tom Messenger said: > Check your circuit for the condition noted on the data sheet regarding > the output voltage EVER getting higher than the input voltage. If this > happens, a parasitic SCR gets turned on in the LP2986 and it will then > get very hot. The data sheet tells how to avoid this. So even if you > don't think that is the problem, try the schottky from Vin to Vout > (cathode to Vin) as the datasheet suggests. Make sure to put it RIGHT on > the regulator with shortest leads possible. That gets my vote too! Also, the motor diode should be a fast diode if you are doing PWM... A schottky is a good choice there, based on the voltages you are using. -Bob -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> Not the tidiest schematic I'm afraid... Eagle and I don't get along > very well. By the way, in the schematic editor you can export the schematic to an image file. Unfortunately this only makes a BMP file, but you can use just about any image manipulation program to convert it to a GIF, which is a good choice for such line art. That way you can spare us the Eagle "+" signs and stuff that make the schematic hard to read, not to mention avoid wasting the bandwidth on the window borders. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseME.....mitvma.mit.edu>

Hi, I think that when you go below 6V something maybe starts to oscillate and thus causes all the problems. Make sure you have at least 2.2 uF cap on the regulator input, as stated in the data sheet otherwise the regulator may be unstable. *********** REPLY SEPARATOR *********** On 25/04/2003 at 17:11 stanton54 wrote: {Quote hidden}>I don't think that's the problem since it works fine as long as the >battery stays above ~ 6 V. I can speed up and slow down the motor and >turn it on and off and everything works fine. There is a diode going >backwards across the motor and 3 capacitors, plus a 10 uF cap right >next to the regulator. I also tried unplugging the motor as soon as it >shut off but the regulator still started getting hot. > >There is another regulator on the board, an LM2940, which interestingly >seems to be OK. I don't think anything hooked up to the 2986 is causing >trouble - the AVR stays cool and the R/C receiver isn't bothering it. > >I will draw a schematic as soon as I finish downloading Eagle. > >Bob Blick wrote: >> >> Is it possible the circuit is turning the motor on and off repeatedly? >> That could generate all sorts of mayhem, especially if you have no >> provision made for catching released energy from the motor. At the very >> least you should probably have a catch diode across the motor. Also you >> may need some bulk capacitance across the battery voltage. >> >> More description of the circuit or a snip of the schematic would help >> further diagnosis. >> >> Cheerful regards, >> >> Bob >> >> -- >> http://www.piclist.com#nomail Going offline? Don't AutoReply us! >> email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body ~~~~~~~~~~~~~~oOo~~~~~~~~~~~~~~~ Ofer Saferman, M.Sc. Senior Design Engineer Paragon Communications 6 Pal-Yam Haifa, 33095 Israel Phone: +972-4-8642775 Fax.: +972-4-8642737 e-mail: RemoveMEoferspam_OUTKILLspamparagoncommtech.com -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTspammitvma.mit.edu>

On Saturday 26 April 2003 04:35 am, Olin Lathrop wrote: > > Not the tidiest schematic I'm afraid... Eagle and I don't get > > along very well. > > By the way, in the schematic editor you can export the schematic to > an image file. Unfortunately this only makes a BMP file, but you > can use just about any image manipulation program to convert it to > a GIF, which is a good choice for such line art. That way you can > spare us the Eagle "+" signs and stuff that make the schematic hard > to read, not to mention avoid wasting the bandwidth on the window > borders. Actually, at least in the version I have it makes PNG files, which are even better than GIFs. -- Ned Konz http://bike-nomad.com GPG key ID: BEEA7EFE -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu>

I tried adding an ordinary diode but as I expected it didn't work. The local RadioShack doesn't have any Schottky diodes (since that isn't a brand of cellphone ;) ) so I won't be able to get any for a while. For now I've 'solved' the problem by adding a separate 9V battery to run the electronic bits. Hopefully the diode will fix things and I'll be able to ditch the extra weight. Olin - thanks for the Eagle tip, I will try that next time. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>By the way, in the schematic editor you can export the schematic to an >image file. Unfortunately this only makes a BMP file, but you can use I was under the impression that you can run the cam processor on the schematic and export as whatever you like. But I have not used Eagle enough yet. It is worth a try. I have chosen the eagle->cam[Post Script]->ghostview->pdf way and I keep to it. Digital print shops take pdf and once you make them understand that 'shrink to fit' and 'expand to fit' must be ticked OFF int eh print options, and that pdf files do not damage Macs, they will do the necessary. Registration is very good on film at A4 size. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I was under the impression that you can run the cam processor on the schematic and export as whatever you like. The CAM processor is a sort of object-oriented output utility for getting data to board houses, automated CNC equipment, and so on. It only works on the board, and it is not the same as the image export capability (for instance, it generally lacks color, as far as I know.) The image export feature does different and also useful things. It seems to default to BMP files at several points, but apparently you can override it to make a .PNG instead... BillW -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads