S Keith used his keyboard to write :> On Wednesday, February 25, 2015 at 9:39:54 AM UTC-7, John Fields wrote: >> On Wed, 25 Feb 2015 19:10:27 +1100, John G <john.g@green.com> wrote: >> >>> jurb6006@gmail.com pretended : >>>>> "Connect 300ohms to +12V and 100 ohms to 0v and the mid point is 3V." >>>> You are wasting 40 mA ! You Austrtalians think the world is made out of >>>> resources don't you ? >>> >>>> You're almost as bad as us. >>> >>> It will work though and is at level the OP can understand >>> Unlike JFs answer which ofers a data sheet to an IC that is most likely >>> way out of the OPS realm to understand much less build. >>> JF too often does this just to show off that he knows more than the >>> resrt of us. :-? >> >> --- >> Perhaps you give the OP too little credit. >> >> In any case, it's only a baby step from the data sheet to Digi-key's >> part selector where there's a part number for the fixed 3-volt >> regulator in most any package you'd like. >> >> Sorry if the leap was too much for you. >> >> John Fields> All, thank you for your respective inputs.> John,> Thank you for going one step further and giving me some credit. I > successfully simulated the voltage divider circuit in Qucs and modeled the > fan with a resistor. The resulting change in the voltage and current at the > divider was concerning.> My lack of experience is painfully evident; however, when I'm pointed down a > path and there are resources available, I can usually work through it.> The linked component looks like it's exactly what I need, and the price is > right. The TO-92 package seems most practical. Please confirm my > interpretation:> PS 12V+ to IN > PS - to GND > LP2950 out + and GND provides 3V, 100ma provided input is > 600mV and < 30V. > I assume the wattages much match, i.e., 0.3W minimum.> This would allow me to use the same 12V PS to drive the fan provided it can > supply the minimum watts and voltage to the VR.> How could I pull the current down to 2mA? A resistor would drop the voltage, > right?> Thanks,> SteveJF, I rest my case. We don't know what the application is but the above question reveals a basic ignorance of OHMS Law so :-? -- John G Sydney.
Using a 12V 2A power supply direct and with 3V voltage divider?
Started by ●February 24, 2015
Reply by ●February 25, 20152015-02-25
Reply by ●February 25, 20152015-02-25
On Wed, 25 Feb 2015 13:19:33 -0800, S Keith wrote:> On Wednesday, February 25, 2015 at 9:39:54 AM UTC-7, John Fields wrote: >> On Wed, 25 Feb 2015 19:10:27 +1100, John G <john.g@green.com> wrote: >> >> >jurb6006@gmail.com pretended : >> >>> "Connect 300ohms to +12V and 100 ohms to 0v and the mid point is >> >>> 3V." >> > >> >> You are wasting 40 mA ! You Austrtalians think the world is made out >> >> of resources don't you ? >> > >> >> You're almost as bad as us. >> > >> >It will work though and is at level the OP can understand Unlike JFs >> >answer which ofers a data sheet to an IC that is most likely way out >> >of the OPS realm to understand much less build. >> >JF too often does this just to show off that he knows more than the >> >resrt of us. :-? >> >> --- >> Perhaps you give the OP too little credit. >> >> In any case, it's only a baby step from the data sheet to Digi-key's >> part selector where there's a part number for the fixed 3-volt >> regulator in most any package you'd like. >> >> Sorry if the leap was too much for you. >> >> John Fields > > All, thank you for your respective inputs. > > John, > > Thank you for going one step further and giving me some credit. I > successfully simulated the voltage divider circuit in Qucs and modeled > the fan with a resistor. The resulting change in the voltage and > current at the divider was concerning. > > My lack of experience is painfully evident; however, when I'm pointed > down a path and there are resources available, I can usually work > through it. > > The linked component looks like it's exactly what I need, and the price > is right. The TO-92 package seems most practical. Please confirm my > interpretation: > > PS 12V+ to IN PS - to GND LP2950 out + and GND provides 3V, 100ma > provided input is > 600mV and < 30V. I assume the wattages much match, > i.e., 0.3W minimum.The input voltage has to be equal or greater to the output voltage plus the dropout. So, over the full temperature range, 3.6V or more. You've got 12V, so that's not an issue. I don't know what you mean by "wattages must match". The regulator will burn up some insignificant amount that it needs for its internal circuitry, plus (output current) * (input voltage - output voltage). In your case that's about 18mW. Looking at the numbers for the TO-92 package, you'll see an (insignificant) 3 degree rise from case to junction.> This would allow me to use the same 12V PS to drive the fan provided it > can supply the minimum watts and voltage to the VR. > > How could I pull the current down to 2mA? A resistor would drop the > voltage, right?The current drawn by the 3V rail that you make will be determined by whatever you hang off of it. If you've got something that consumes 2mA at 3V, that's what will get consumed. For any two-terminal network, the current draw is a function of voltage -- you cannot set both current and voltage externally. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●February 25, 20152015-02-25
On Wednesday, February 25, 2015 at 4:31:09 PM UTC-7, John G wrote:> S Keith used his keyboard to write : > > On Wednesday, February 25, 2015 at 9:39:54 AM UTC-7, John Fields wrote: > >> On Wed, 25 Feb 2015 19:10:27 +1100, John G <john.g@green.com> wrote: > >> > >>> jurb6006@gmail.com pretended : > >>>>> "Connect 300ohms to +12V and 100 ohms to 0v and the mid point is 3V." > >>>> You are wasting 40 mA ! You Austrtalians think the world is made out of > >>>> resources don't you ? > >>> > >>>> You're almost as bad as us. > >>> > >>> It will work though and is at level the OP can understand > >>> Unlike JFs answer which ofers a data sheet to an IC that is most likely > >>> way out of the OPS realm to understand much less build. > >>> JF too often does this just to show off that he knows more than the > >>> resrt of us. :-? > >> > >> --- > >> Perhaps you give the OP too little credit. > >> > >> In any case, it's only a baby step from the data sheet to Digi-key's > >> part selector where there's a part number for the fixed 3-volt > >> regulator in most any package you'd like. > >> > >> Sorry if the leap was too much for you. > >> > >> John Fields > > > All, thank you for your respective inputs. > > > John, > > > Thank you for going one step further and giving me some credit. I > > successfully simulated the voltage divider circuit in Qucs and modeled the > > fan with a resistor. The resulting change in the voltage and current at the > > divider was concerning. > > > My lack of experience is painfully evident; however, when I'm pointed down a > > path and there are resources available, I can usually work through it. > > > The linked component looks like it's exactly what I need, and the price is > > right. The TO-92 package seems most practical. Please confirm my > > interpretation: > > > PS 12V+ to IN > > PS - to GND > > LP2950 out + and GND provides 3V, 100ma provided input is > 600mV and < 30V. > > I assume the wattages much match, i.e., 0.3W minimum. > > > This would allow me to use the same 12V PS to drive the fan provided it can > > supply the minimum watts and voltage to the VR. > > > How could I pull the current down to 2mA? A resistor would drop the voltage, > > right? > > > Thanks, > > > Steve > > JF, I rest my case. We don't know what the application is but the above > question reveals a basic ignorance of OHMS Law so :-? > > -- > John G Sydney.Thanks John G. While my ignorance is vast, I know V=IR. I need to supply 3V, 2mA - not meet the requirement of a 3V, 2mA load. I have a 12V PWM controlled fan. I don't know anything other than it takes 12V ~1.6A to run it and a 3V, 2mA signal to activate it. I'm trying to accomplish this. If I supply a higher current, I am concerned I might damage something. Steve
Reply by ●February 26, 20152015-02-26
S Keith wrote:> Thanks John G. While my ignorance is vast, I know V=IR. I need to supply 3V, 2mA** You are being far to literal. 3V at 2mA MEANS with a voltage supply of 3V, the LOAD draws 2mA.> I have a 12V PWM controlled fan. > I don't know anything other than it takes 12V ~1.6A** That is a very big PWM fan. High time you supplied a link to the thing.> to run it and a 3V, 2mA signal to activate it.** PWM fans normally require a PWM signal to control them. You are contradicting yourself not making sense. ... Phil
Reply by ●February 26, 20152015-02-26
On Wednesday, February 25, 2015 at 10:15:00 PM UTC-7, Phil Allison wrote:> S Keith wrote: >=20 > =20 > > Thanks John G. While my ignorance is vast, I know V=3DIR. I need to sup=ply 3V, 2mA>=20 > ** You are being far to literal.=20 >=20 > 3V at 2mA MEANS with a voltage supply of 3V, the LOAD draws 2mA.=20 >=20 >=20 > > I have a 12V PWM controlled fan. > > I don't know anything other than it takes 12V ~1.6A >=20 >=20 > ** That is a very big PWM fan.=20 >=20 > High time you supplied a link to the thing.=20 >=20 >=20 > > to run it and a 3V, 2mA signal to activate it. >=20 >=20 > ** PWM fans normally require a PWM signal to control them. >=20 > You are contradicting yourself not making sense. >=20 >=20 > ... PhilIf I could link it for you, I would know more about it. It's the cooling f= an for a Honda Civic Hybrid battery pack. It's a "squirrel cage" blower ty= pe fan. It blows air into the trunk thereby creating a vacuum in the seale= d case, which then draws cabin air in through the battery pack and the rela= ted electronics. I "discovered" that I can activate the fan with a multimeter that puts out = a 3V, 2mA current. I wish to duplicate this to drive the fan as I thought = it would be a simple solution compared to figuring out how to supply a PWM = signal. I do not know the components involved or their limitations. I only know th= e "experimental" input and outcome. Steve
Reply by ●February 26, 20152015-02-26
On Wed, 25 Feb 2015 13:19:33 -0800 (PST), S Keith <stkeith11@gmail.com> wrote:>On Wednesday, February 25, 2015 at 9:39:54 AM UTC-7, John Fields wrote: >> On Wed, 25 Feb 2015 19:10:27 +1100, John G <john.g@green.com> wrote: >> >> >jurb6006@gmail.com pretended : >> >>> "Connect 300ohms to +12V and 100 ohms to 0v and the mid point is 3V." >> > >> >> You are wasting 40 mA ! You Austrtalians think the world is made out of >> >> resources don't you ? >> > >> >> You're almost as bad as us. >> > >> >It will work though and is at level the OP can understand >> >Unlike JFs answer which ofers a data sheet to an IC that is most likely >> >way out of the OPS realm to understand much less build. >> >JF too often does this just to show off that he knows more than the >> >resrt of us. :-? >> >> --- >> Perhaps you give the OP too little credit. >> >> In any case, it's only a baby step from the data sheet to Digi-key's >> part selector where there's a part number for the fixed 3-volt >> regulator in most any package you'd like. >> >> Sorry if the leap was too much for you. >> >> John Fields > >All, thank you for your respective inputs. > >John, > >Thank you for going one step further and giving me some credit. I successfully simulated the voltage divider circuit in Qucs and modeled the fan with a resistor. The resulting change in the voltage and current at the divider was concerning. > >My lack of experience is painfully evident; however, when I'm pointed down a path and there are resources available, I can usually work through it. > >The linked component looks like it's exactly what I need, and the price is right. The TO-92 package seems most practical. Please confirm my interpretation: > >PS 12V+ to IN >PS - to GND >LP2950 out + and GND provides 3V, 100ma provided input is > 600mV and < 30V. I assume the wattages much match, i.e., 0.3W minimum. > >This would allow me to use the same 12V PS to drive the fan provided it can supply the minimum watts and voltage to the VR. > >How could I pull the current down to 2mA? A resistor would drop the voltage, right?--- I don't know what you mean by: "the wattages must match." You don't need to do anything but connect the regulator's input to +12V and its output to your 3V load, and whatever current your load wants - up to 100mA - the regulator will supply and keep the input to the load at 3V. John Fields
Reply by ●February 26, 20152015-02-26
On Thu, 26 Feb 2015 10:31:01 +1100, John G <john.g@green.com> wrote:>S Keith used his keyboard to write : >> On Wednesday, February 25, 2015 at 9:39:54 AM UTC-7, John Fields wrote: >>> On Wed, 25 Feb 2015 19:10:27 +1100, John G <john.g@green.com> wrote: >>> >>>> jurb6006@gmail.com pretended : >>>>>> "Connect 300ohms to +12V and 100 ohms to 0v and the mid point is 3V." >>>>> You are wasting 40 mA ! You Austrtalians think the world is made out of >>>>> resources don't you ? >>>> >>>>> You're almost as bad as us. >>>> >>>> It will work though and is at level the OP can understand >>>> Unlike JFs answer which ofers a data sheet to an IC that is most likely >>>> way out of the OPS realm to understand much less build. >>>> JF too often does this just to show off that he knows more than the >>>> resrt of us. :-? >>> >>> --- >>> Perhaps you give the OP too little credit. >>> >>> In any case, it's only a baby step from the data sheet to Digi-key's >>> part selector where there's a part number for the fixed 3-volt >>> regulator in most any package you'd like. >>> >>> Sorry if the leap was too much for you. >>> >>> John Fields > >> All, thank you for your respective inputs. > >> John, > >> Thank you for going one step further and giving me some credit. I >> successfully simulated the voltage divider circuit in Qucs and modeled the >> fan with a resistor. The resulting change in the voltage and current at the >> divider was concerning. > >> My lack of experience is painfully evident; however, when I'm pointed down a >> path and there are resources available, I can usually work through it. > >> The linked component looks like it's exactly what I need, and the price is >> right. The TO-92 package seems most practical. Please confirm my >> interpretation: > >> PS 12V+ to IN >> PS - to GND >> LP2950 out + and GND provides 3V, 100ma provided input is > 600mV and < 30V. >> I assume the wattages much match, i.e., 0.3W minimum. > >> This would allow me to use the same 12V PS to drive the fan provided it can >> supply the minimum watts and voltage to the VR. > >> How could I pull the current down to 2mA? A resistor would drop the voltage, >> right? > >> Thanks, > >> Steve > >JF, I rest my case. We don't know what the application is but the above >question reveals a basic ignorance of OHMS Law so :-?--- All it reveals is that he's confused and needs a little help, not insults, to get on track. In the same vein, it seems you're also confused about a series resistor "working" as a ballast, especially with your admission of being ignorant about the OP's application.
Reply by ●February 26, 20152015-02-26
On Thu, 26 Feb 2015 06:39:34 -0800 (PST), S Keith <stkeith11@gmail.com> wrote:>On Wednesday, February 25, 2015 at 10:15:00 PM UTC-7, Phil Allison wrote: >> S Keith wrote: >> >> >> > Thanks John G. While my ignorance is vast, I know V=IR. I need to supply 3V, 2mA >> >> ** You are being far to literal. >> >> 3V at 2mA MEANS with a voltage supply of 3V, the LOAD draws 2mA. >> >> >> > I have a 12V PWM controlled fan. >> > I don't know anything other than it takes 12V ~1.6A >> >> >> ** That is a very big PWM fan. >> >> High time you supplied a link to the thing. >> >> >> > to run it and a 3V, 2mA signal to activate it. >> >> >> ** PWM fans normally require a PWM signal to control them. >> >> You are contradicting yourself not making sense. >> >> >> ... Phil > >If I could link it for you, I would know more about it. It's the cooling fan for a Honda Civic Hybrid battery pack. It's a "squirrel cage" blower type fan. It blows air into the trunk thereby creating a vacuum in the sealed case, which then draws cabin air in through the battery pack and the related electronics. > >I "discovered" that I can activate the fan with a multimeter that puts out a 3V, 2mA current. I wish to duplicate this to drive the fan as I thought it would be a simple solution compared to figuring out how to supply a PWM signal. > >I do not know the components involved or their limitations. I only know the "experimental" input and outcome.--- Steve, forget the regulator for the time being. How did you use your multimeter to arrive at 3V 2mA?
Reply by ●February 26, 20152015-02-26
On Thursday, February 26, 2015 at 10:46:10 AM UTC-7, John Fields wrote:> > --- > I don't know what you mean by: "the wattages must match." > > You don't need to do anything but connect the regulator's input to > +12V and its output to your 3V load, and whatever current your load > wants - up to 100mA - the regulator will supply and keep the input > to the load at 3V. > > John FieldsI meant that since the VR puts out 0.3W, I must meet that input plus a little for inefficiencies. With 12V/2.1A PS, that shouldn't be an issue. It's probably been lost in the mess, but I'm trying to simulate what amounts to a PWM signal, so I need to cut the current. Reading up on computer fan PWM control suggests 3.3V/5-8mA max if this fan is analogous. Steve
Reply by ●February 26, 20152015-02-26
On Thursday, February 26, 2015 at 10:59:15 AM UTC-7, John Fields wrote:> Steve, forget the regulator for the time being. >=20 > How did you use your multimeter to arrive at 3V 2mA?I was probing the PWM/tach wires of the fan with my multimeter set to sense= 200 Ohms. 12V was supplied to power, but PWM/speed were disconnected. To = my shock, the fan spooled up. I checked the multimeter with another, and t= he output of the multimeter at that resistance setting was 3V/2mA.
