5v stepped down to 200 millivolts / can it be done?

[customcounts]

Ok here's the deal, I have a 5 volt reference wire and I'm trying to achieve an adjustable voltage of 0 ~ 1500 millivolts. The biggest problem with this is that there is no measureable load, I have a pretty good meter and cannot get an amper reading on my signal feed. How would I go about stepping down this voltage? I've tried resistors from 1ohm at 1/4 amp to 60ohm at 60 amps, I've also stepped the voltage down using an adjustable voltage regulator and a pot but the lowest I could get the voltage was of course 1.25v exactly what the regulator limits. Any help would be much appreciated.

 

[mvs sarma]

Ok here's the deal, I have a 5 volt reference wire and I'm trying to achieve an adjustable voltage of 0 ~ 1500 millivolts. The biggest problem with this is that there is no measureable load, I have a pretty good meter and cannot get an amper reading on my signal feed. How would I go about stepping down this voltage? I've tried resistors from 1ohm at 1/4 amp to 60ohm at 60 amps, I've also stepped the voltage down using an adjustable voltage regulator and a pot but the lowest I could get the voltage was of course 1.25v exactly what the regulator limits. Any help would be much appreciated.

If you use N Channel J-FET like J310 or BF245 as a constant current source,with input at 5V, and with a resistance at the source to ground, you get the needed voltage across the said resistor. There on you can convert it as a pot and get any ratio you need. similarly, ICL8069 current source (if I remember) can also be used. you may recollect this device as used in DPMs as External reference voltage generation on ICL7106(7).

 

[Boncuk]

the lowest I could get the voltage was of course 1.25v exactly what the regulator limits. Any help would be much appreciated.

that applies if you use the voltage regulator as a voltage regulator. How about using it as a current regulator?

With an LM317L you might reduce current to 1mA resulting in a current of 1.25mA with a 1K reference resistor (feedback), hence resulting in a minimum voltage of 125mV across a burden resistor of 100Ω.

Generating a current of less than 1mA takes the device out of limits. The constant current is wideley independent of input voltage and ambient temperature. The formula to calculate for refererence current: Iref=Uref/Rf, for the previously described case this is 1.25/1000 equalling 1.25mA. For voltage calculation of the burden resistor apply Ohm's law.

Boncuk

 

[mvs sarma]

that applies if you use the voltage regulator as a voltage regulator. How about using it as a current regulator?

With an LM317L you might reduce current to 1mA resulting in a current of 1.25mA with a 1K reference resistor (feedback), hence resulting in a minimum voltage of 125mV across a burden resistor of 100Ω.

Generating a current of less than 1mA takes the device out of limits. The constant current is wideley independent of input voltage and ambient temperature. The formula to calculate for refererence current: Iref=Uref/Rf, for the previously described case this is 1.25/1000 equalling 1.25mA. For voltage calculation of the burden resistor apply Ohm's law.

Boncuk

the OP has indicated that he doesn't need much current. LM317 iss safely avoided as it needs a min current.
he/she can have a potentoimeter at the bottom line for getting 1.5V as he wants it. the wiper would deliver variable output with NO MUCH Load as the Op indicated.to be accurate enough, perhaps the load should be less than 1% of the load on the current source.

 

[customcounts]

not a clue

ok advice much appreciated, but I am new to this electronics talk and i'm trying to reserch to figure out what all of this means, and I'm not doing a very good job at it. if you could please break this down into more simple terms or possibly a circuit diagram. Again thanks for the help. Matt

 

[philba]

what happens when you apply -1.05 V to the control input of the 317? I know it's out of spec but i've heard of people doing that to get really low voltages.

 

[Boncuk]

the OP has indicated that he doesn't need much current. LM317 iss safely avoided as it needs a min current.
he/she can have a potentoimeter at the bottom line for getting 1.5V as he wants it. the wiper would deliver variable output with NO MUCH Load as the Op indicated.to be accurate enough, perhaps the load should be less than 1% of the load on the current source.

Hi mvs sarma,

you will certainly admit that any voltage drop is the result of resistance and current flow. The minimum current for the LM317L is 1mA according to the data sheet. Simulations have proved that it works down to 500µA. The OP wants voltages down to 200mV. With the given example it is already far below his requirement and based on a maximum voltage of 10V across the burden resistor. Halfing the resistance of the burden will result in half of the voltage drop.

Boncuk

 

[Boncuk]

Hi customcounts,

here's the circuit as suggested.

Boncuk

 

[kchriste]

The biggest problem with this is that there is no measureable load.

That's not a problem, but an advantage. All you'll need is a POT and a resistor if the load is very small. How small is the load current? Is the 5V regulated? Where does the 5V come from? We really need to know this to give you a proper answer with a schematic.

 

[customcounts]

Not sure how

That's not a problem, but an advantage. All you'll need is a POT and a resistor if the load is very small. How small is the load current? Is the 5V regulated? Where does the 5V come from? We really need to know this to give you a proper answer with a schematic.

ok the supply voltage is regulated it carries .11 amps but the reference voltage of 200mV has no load its monitored somehow without a load. Correct me if I'm wrong and tell me what meter I need to measure it properly. Thanks again

 

[customcounts]

Ok, I've achieved the 200mV, adjustable at that!!! Thanks Again. Now the next step is to design a digital voltage display so that I can monitor the voltage and dial it in while driving. This will be a solid mounted fixture in a prototype vehicle I'm building. I've looked at different articles on 7 seg displays but quite honestly this is so far out of my league that I need some serious baby steps. I've realized that this is much needed with the endevor I've taken, so I'm reading until my eyes bleed and trying to learn all the talk (as well as complete the project at hand) I CAN NOT say thanks enough for the help you have provided thus far and I hope to soon be educated and a burden no more.

 

[kchriste]

I've looked at different articles on 7 seg displays but quite honestly this is so far out of my league that I need some serious baby steps.

The easiest thing to do would be to buy a cheap multimeter at a hardware store, etc and set it read the 200mV.
Something like this:
**broken link removed**
Or, to look more professional at a cheaper cost, buying a panel meter like this one:
**broken link removed**
would be the easiest solution for someone with limited building experience and cheaper than what an experienced hobbyist could build themselves.

 

[blueroomelectronics]

Yet another hydrogen generator for a car. PS they don't work.

 

[customcounts]

ooohhhh close but not quite

Yet another hydrogen generator for a car. PS they don't work.

oh yeah hydrogen is everything everybody blah blah blah blah. Old news, as a matter of fact I was attacked today by some bum who needed a shower telling me how hydrogen was all that. Unfortunately for him I did extensive research and development on my own generator just over 2 years ago. I've got the lawn mower running off a generator I designed. Simple 6" housing tube/rod & Plate combo with a measured output of 6 liters per minute at a magical amperage draw of only 2.6 amps. I had the answer to all his questions and finally ended the conversation with "so let's see the one on your car!" yep just as I guessed can't afford to shower or even try to build his own HHO gen.

No this is my personal attempt to modify an epromed p72 ECM to run my creations. The only set back is a simulated voltage to feed a custom mated trip-tronic transmission and allow the traction control to full pull both wheels without engine brake or selective dif throw.

and for the record hydrogen has been proven to improve efficiency on many different engines, (with proper fuel management) and as I stated before I've got a riding mower that runs on HHO with (as I boast) one of the highest output generators in the world per amp. If you ever feel like mowing a lawn on nothin but tap water just come on over cause it still sucks to mow even if the fuel is free.

 

[Nigel Goodwin]

If you ever feel like mowing a lawn on nothin but tap water just come on over cause it still sucks to mow even if the fuel is free.

How is it 'free', where do you get free hydrogen from?.

 

[Boncuk]

How is it 'free', where do you get free hydrogen from?.

He can get it almost free using a Hoffmann electrolytic splitter. Splits water into 1 part oxygen and 2 parts hydrogen.

A bit dangerous though.

 

[kchriste]

How is it 'free', where do you get free hydrogen from?.

I hear there's a lot just "lying around" in/on Jupiter.

Old news, as a matter of fact I was attacked today by some bum who needed a shower telling me how hydrogen was all that.

Sounds like he needed some O with his H.

 

[blueroomelectronics]

I've got a riding mower that runs on HHO with (as I boast) one of the highest output generators in the world per amp. If you ever feel like mowing a lawn on nothin but tap water just come on over cause it still sucks to mow even if the fuel is free.

So sell it, become a millionaire. What's stopping you?

 

[robb01]

**broken link removed**

 

[customcounts]

water.... It's not absolutely free but 22oz of water from my tap in the house is like .0026 cents and that can generate enough HHO to mow my lawn 4 times witch is about 8 hours of run time.

It's actually very interesting and possibly the most simple thing in the world to accomplish. Pass electric current through water H2O, blow the molecules apart and presto changeo Hydrogen and Oxygen.