Post by thread:[EE]: Suggestion for voltage regulator.

Hello All, I have a project that I'm working on that runs of two D cells in series. I'm using a 16C711 that works from 2.5-5.5V. On the ADC port I have a 3VDC pressure transducer with a output of 0-60mV. When a certian pressure is reached a solenoid valve opens. Here's my problem. I want this to be effecient on battery power so I'd like to run both sensor and pic at 2.5V trouble is even LDO's will dropout at about 2.7V. The solenoid works to about 2.4V. What I was thinking of doing is not using a regulator so the voltage would vary over battery life about 1.6-1.25. Vref (I have it set at about 70mV) should drop with respect to battery and so should the output of the sensor (it's a wheatstone bridge configuration). I also have the pic calibrate on boot. So these three attributes combined I would believe would be enough to not have to use a regulator. Any thoughts? Any ideas on a reg that would output 2.5V until the voltage dropped below 2.5V? Aaron -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

On 4 Jun 2002 at 11:41, A.J. Tufgar wrote: > Hello All, > I have a project that I'm working on that runs of two D cells > in series. I'm using a 16C711 that works from 2.5-5.5V. On the ADC > port I have a 3VDC pressure transducer with a output of 0-60mV. When a > certian pressure is reached a solenoid valve opens. > > Here's my problem. I want this to be effecient on battery power so I'd > like to run both sensor and pic at 2.5V trouble is even LDO's will > dropout at about 2.7V. The solenoid works to about 2.4V. > > What I was thinking of doing is not using a regulator so the voltage > would vary over battery life about 1.6-1.25. Vref (I have it set at > about 70mV) should drop with respect to battery and so should the output > of the sensor (it's a wheatstone bridge configuration). I also have the > pic calibrate on boot. So these three attributes combined I would > believe would be enough to not have to use a regulator. > > Any thoughts? Any ideas on a reg that would output 2.5V until the > voltage dropped below 2.5V? Shunt Regulator. (Zener). {Quote hidden}> > Aaron > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body > > * | __O Thomas C. Sefranek tcsKILLspamcmcorp.com |_-\<,_ Amateur Radio Operator: WA1RHP (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz ARRL Instructor, Technical Specialist, VE Contact. hamradio.cmcorp.com/inventory/Inventory.html http://www.harvardrepeater.org -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

A fresh set of alkalines will give you a pretty constant voltage that you should be able to calibrate to upon power up and provide useful accuracy. Once the batteries reach the end of their useful life, the voltage will take a steep plunge and there is no real advantage of tracking or calibrating your pic reference to it. Two aging cells in series providing 2.5 volts means it is already on a rapid avalanche to zero. A fresh set of cells is the only reliable fix. Rick "A.J. Tufgar" wrote: {Quote hidden}> Hello All, > I have a project that I'm working on that runs of two D cells > in series. I'm using a 16C711 that works from 2.5-5.5V. On the ADC > port I have a 3VDC pressure transducer with a output of 0-60mV. When a > certian pressure is reached a solenoid valve opens. > > Here's my problem. I want this to be effecient on battery power so I'd > like to run both sensor and pic at 2.5V trouble is even LDO's will > dropout at about 2.7V. The solenoid works to about 2.4V. > > What I was thinking of doing is not using a regulator so the voltage > would vary over battery life about 1.6-1.25. Vref (I have it set at > about 70mV) should drop with respect to battery and so should the output > of the sensor (it's a wheatstone bridge configuration). I also have the > pic calibrate on boot. So these three attributes combined I would > believe would be enough to not have to use a regulator. > > Any thoughts? Any ideas on a reg that would output 2.5V until the > voltage dropped below 2.5V? > > Aaron > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> On 4 Jun 2002 at 11:41, A.J. Tufgar wrote: > > > Hello All, > > I have a project that I'm working on that runs of two D cells > > in series. I'm using a 16C711 that works from 2.5-5.5V. On the ADC > > port I have a 3VDC pressure transducer with a output of 0-60mV. When a > > certian pressure is reached a solenoid valve opens. > > > > Here's my problem. I want this to be effecient on battery power so I'd > > like to run both sensor and pic at 2.5V trouble is even LDO's will > > dropout at about 2.7V. The solenoid works to about 2.4V. > > Any thoughts? Any ideas on a reg that would output 2.5V until the > > voltage dropped below 2.5V? It shouldn't be that hard to make a low-dropout regulator with three transistors. What sort of current does this circuit require? If it's only <100mA etc than this should do the trick: In 3.4v to 2.52v ------*---*-----------, | | | R | PNP R | E lo-sat | *--B | | C-----------|------*------ 2.5v out | | | | | | C | R B--------------*-, | E | | any | C | NPN | any B---* | NPN E | | | R | | | gnd -----*-----------------*----*------ gnd I've tested lo-sat transistors here that will do better than 20mV C-E at 50mA, the bad news is that they are TO-220 pack power trannys. I'm sure you can find a decent lo-sat tranny in a small pack like standard TO-92 etc. A fet will do the low drop but will be almost impossible to drive with only 2.5v as your input voltage. :o) -Roman -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

Roman, I saw the feedback but I don't see anywhere the reference, maybe you should explain a little. My impresion is that stabiliser is strongly dependent with the load parameters. Could you point also what transistors did you found with 20mV Vce at Ic = 50mA ? thanks, Vasile http://www.geocities.com/vsurducan On Thu, 6 Jun 2002, Roman Black wrote: {Quote hidden}> > On 4 Jun 2002 at 11:41, A.J. Tufgar wrote: > > > > > Hello All, > > > I have a project that I'm working on that runs of two D cells > > > in series. I'm using a 16C711 that works from 2.5-5.5V. On the ADC > > > port I have a 3VDC pressure transducer with a output of 0-60mV. When a > > > certian pressure is reached a solenoid valve opens. > > > > > > Here's my problem. I want this to be effecient on battery power so I'd > > > like to run both sensor and pic at 2.5V trouble is even LDO's will > > > dropout at about 2.7V. The solenoid works to about 2.4V. > > > > Any thoughts? Any ideas on a reg that would output 2.5V until the > > > voltage dropped below 2.5V? > > > It shouldn't be that hard to make a low-dropout > regulator with three transistors. What sort of > current does this circuit require? If it's only > <100mA etc than this should do the trick: > > In 3.4v to 2.52v > ------*---*-----------, > | | | > R | PNP R > | E lo-sat | > *--B | > | C-----------|------*------ 2.5v out > | | | > | | | > C | R > B--------------*-, | > E | | > any | C | > NPN | any B---* > | NPN E | > | | R > | | | > gnd -----*-----------------*----*------ gnd > > > I've tested lo-sat transistors here that will do > better than 20mV C-E at 50mA, the bad news is that > they are TO-220 pack power trannys. I'm sure you > can find a decent lo-sat tranny in a small pack > like standard TO-92 etc. A fet will do the low > drop but will be almost impossible to drive with > only 2.5v as your input voltage. :o) > -Roman > > -- > http://www.piclist.com hint: To leave the PICList > RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Vasile Surducan wrote: > > Roman, I saw the feedback but I don't see anywhere the reference, maybe > you should explain a little. My impresion is that stabiliser is strongly > dependent with the load parameters. Could you point also what transistors > did you found with 20mV Vce at Ic = 50mA ? Hi Vasile! :o) The transistors I have the most of are BD203 (NPN) and BD204 (PNP). I often use them as low-sat drivers, at 50mA Ic you get about 20mV C-E on the NPN but the PNP is a fraction worse. The BD203 is TO-220, 60v 8A 60w. Used in the TV trade for vertical power amp in ancient TVs. About $0.20 US. Absolutely brilliant for the $$, almost indestructable and about as good as trannys got before the fet fad. A similar "modern" transistor is the TIP41C, ok for low-sat use at 170mV C-E at 1A, 260mV C-E at 2A. Not quite as good as BD203 for very low currents though. Both these transistors will drive 1A loads and stay cool with no heatsink, and are more robust, easier to drive and cheaper than similar fets (but that's a whole new argument!) The circuit I proposed is a simple low-dropout regulator to give regulated 2.5vdc from 2x 1.5v cells. The regulation should be quite independent of load parameters, it's determined by the B-E junction of the last transistor and since that transistor passes very little current and won't get hot it should regulate quite well. There is plenty of gain and voltage headroom to drive the main tranny well into saturation even with 2.52v input and 2.50v output. :o) -Roman {Quote hidden}> > > > Any thoughts? Any ideas on a reg that would output 2.5V until the > > > > voltage dropped below 2.5V? > > > > > > It shouldn't be that hard to make a low-dropout > > regulator with three transistors. > > In 3.4v to 2.52v > > ------*---*-----------, > > | | | > > R | PNP R > > | E lo-sat | > > *--B | > > 1.92v | C-----------|------*------ 2.5v out > > | | | > > | | | > > C | R > > B--------------*-, | > > E 0.6v | | > > any | C | > > NPN | any B---* 0.6v > > | NPN E | > > | | R > > | | | > > gnd -----*-----------------*----*------ gnd -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads