Author Topic: Variable input using the LM317 regulator question... (Read 7711 times)

windstuffnow · « **on:** June 05, 2006, 09:40:16 PM »

I'm curious if a LM317 regulator would be bothered by constant variable input while regulating the output at a voltage slightly lower than the input. I need it to be able to handle a 3-11 volt input while holding a 3.4volt maximum output.

Also, is there a way to use the same regulator to shut down the circuit when a voltage of 3.6 is reached and come back on when its dropped back to 3.4?

I'm looking to keep the circuit as simple as I can possibly get away with ( as usual ). Remember talk to me like an intrigued learning child as my knowledge of electronics ( although growing slowly ) is still limited...

Thanks in advance to all you "guru's" that can help once again!

.

willib · « **Reply #1 on:** June 05, 2006, 04:06:52 PM »

http://www.national.com/pf/LM/LM317.html

http://cache.national.com/ds/LM/LM117.pdf

yes it should work for your purpose,there are many examples in the pdf of the possible uses of the LM317.

the varible input would be the output from a alt/gen?

"Also, is there a way to use the same regulator to shut down the circuit when a voltage of 3.6 is reached and come back on when its dropped back to 3.4? "

that may need something else, but doable nonetheless..

asheets · « **Reply #2 on:** June 05, 2006, 04:06:55 PM »

I think you'll find the relevent circuit diagram and specs here: http://www.fairchildsemi.com/ds/LM/LM317.pdf

willib · « **Reply #3 on:** June 05, 2006, 04:31:01 PM »

http://www.otherpower.com/images/scimages/2965/eds_circuit.JPG

this one might be just what you need , but you just have to recalculate the resistors needed to get your desired output voltage .

in there somewhere is a set of equations to calculate the desired output voltage..

the circuit i've chosen will shut that baby down with a logic signal.

Bruce S · « **Reply #4 on:** June 05, 2006, 04:32:18 PM »

Ed;

The answer is Kinda sorta.

Using this little workhorse is a great idea.

Here's a few things: The input needs to stay about 2 1/2 volts above the output, so your varying in/out is okay the LM will take it no problem, however in order to have the desired output it'll need to stay up there in the 5 & higher volts input.

The cut in/out voltages can also be done just a little more complex than a standard straight output.

What's the current range? these have a 5A max and will need a heatsink to absorb all the extra heat.

Bruce S

Of course you can use two and build a comparator type circuit for these close tolerences.

commanda · « **Reply #5 on:** June 05, 2006, 04:39:25 PM »

In order to regulate, the input voltage needs to be higher than the output voltage by a certain minimum amount. Without looking up the datasheet, I think it's about 1.2 volts. Below this, it won't actually regulate, but the output voltage will be below your set regulation voltage. There are probably low-dropout versions available.

Not sure what you mean by "shutdown the circuit". Describe better what you mean, and I'll help.

Amanda

windstuffnow · « **Reply #6 on:** June 05, 2006, 05:33:50 PM »

What is the end labeled "TTL" not sure what that is.... is this the Logic circuit your describing? What would the logic circuit consist of?

The shut down may not be necessary as long as the voltage remained the same.

I'll put together a basic regulator circuit and see if I can make some smoke. My main concern was the continuously varying input.

Thanks all !!! That should get me on my way to experimenting....

.

ghurd · « **Reply #7 on:** June 05, 2006, 05:34:20 PM »

Hi Ed,

For 3 ni-cds or ni-mh, 4.5V is good.

There are 3.3V TO-220(-ish) 3 pin regulators for a buck or 2. The output voltage will not go past 3.3V. Simple.

Watch out for lower Vin max, like 10Vmax.

LD1117AV33 ("3.3V regulator rated at 1A. TO-220, low drop out positive regulator. Current limiting and thermal protection. DC input voltage 10 volts. Maximum drop out of 1.3V at 1A. $0.89)

and

LM1085IT-3.3 ("3.3V regulator rated at 3A. TO-220, low drop out positive regulator. current limiting and thermal protection" $1.49)

come to mind on the surplus market in the US. (at BGMicro)

I have replaced transformers with both.

A larger capacitor at the input may help. Rarely, but sometimes, a cap on the output is needed.

G-

willib · « **Reply #8 on:** June 05, 2006, 08:14:22 PM »

" What is the end labeled "TTL" not sure what that is.... is this the Logic circuit your describing? What would the logic circuit consist of? "

most likely it would consist of a circuit that has an analog input and a digital output.

the analog part would monitor the LM317 circuit output and make a decision as to when to turn the LM317 on or off.

commanda · « **Reply #9 on:** June 06, 2006, 04:12:48 AM »

If you are, in fact, trying to charge Ni-Cd batteries, you should be using a constant current charger (which can be done with the LM317), and negative slope detection (voltage) to detect end of charge.

As a minimum, start with the constant current charger, rather than a constant voltage regulator.

Amanda

windstuffnow · « **Reply #10 on:** June 06, 2006, 08:50:37 AM »

Sooo... could that be as simple as adding a 3.3v Zener to tell it when the voltage is up enough to shut down the circuit?

The shut down was actually a secondary thought not sure its really needed as long as everything holds on the voltage end.

.

windstuffnow · « **Reply #11 on:** June 06, 2006, 08:54:59 AM »

I am charging Ni-cad / NiMH batteries from a very tiny wind turbine. It will do about 0-11 volts at a bit over an amp. Trying to keep it simple but safe...

I'll look at a current charger, I think I saw one in the pdf...

Thanks !

.

willib · « **Reply #12 on:** June 06, 2006, 11:24:54 AM »

Vref seems to be the voltage of the battery under charge

at least thats the way it worked out 1.2V / 24 = 50mA..

Hope that helps

commanda · « **Reply #13 on:** June 06, 2006, 11:41:20 AM »

Vref seems to be the voltage of the battery under charge

Vref is the voltage between Vout & Adj. It is a constant 1.2 volts.

Amanda

Bruce S · « **Reply #14 on:** June 06, 2006, 12:03:19 PM »

Ed;

This won't be one of those wonderful "kits" of yours would it?

I just received the one I ordered for our daughter. She's already got the turbine together and was working with the PDF on the wiring part.

I have a small schematic that I plan on using with this to recharge her AA 1500mA NiCd batts with, but I planned on using the LM as a constant voltage output set at 1.3Vdc rather than constant current. Due to having the box to hold 4 of these I felt keeping the output at a constant voltage would be the better way to go. I'm pretty sure tho that by tying a current limting resistor across the adj pin and Vout pin and a little math limiting the Max current is do-able too.

Will let you know the outcome.

FWIW: Your kit outshines the Pico by a 1000%.

I plan on mounting this just outside her window so we'll have not the greatest of wind but there we can take very good measurement of the wind and charging setup.

willib · « **Reply #15 on:** June 06, 2006, 12:05:10 PM »

you're right , i should have read it before posting. thanks

so Ed

Iout = 1.25 / R1

The circuit below is just a way to adjust the current

windstuffnow · « **Reply #16 on:** June 06, 2006, 02:26:57 PM »

Thanks for the kind words about my educational kit, I keep changing little things to make it easier and a little better each time.

This experiment is actually a brain storm of a good friend. I'm trying to figure out how to impliment it into a small turbine, a little larger than the kit.

Keep watching my site... We've been working on some other pretty exciting things, one of which will be posted in a week or so.

I'll throw out a teaser... a low rpm, high voltage minigen - be careful - it will bite you ! Lights an UB LED at an rpm slower than you thought possible... It's difficult to turn it slow enough not to light it ! Teaser ;o)

This project has noting to do with that one though... I'm just haveing one heck of a good time playing with this stuff.

.

ghurd · « **Reply #17 on:** June 06, 2006, 03:34:13 PM »

Hi Bruce,

Don't you feel 1.3V is kind of low? I usually see 1.4~1.45V.

G-

Bruce S · « **Reply #18 on:** June 06, 2006, 04:15:45 PM »

G-

Not really. A standing NiCd is 1.25 and since the first NiCd packs blew up on me using higher charging voltages, I've stayed at the 1.3V range and let the current do the rest.

I've had good luck with this so far( read no exploding batteries) and the packs have the same distance as far as the e-trike goes.

We constantly use about 75% of the rated/confirmed Ahs so this may also help with keeping the NiCds healthy

Our newly built packs are charged this way and they don't get hot at all.

Somewhere I'll find a better way as the packs increase storage.

I have been looking at the Homebrew pulser charger , just too busy (read work) to get into by bag of goodies and build one.

Thoughts?

Bruce S

ghurd · « **Reply #19 on:** June 06, 2006, 04:44:01 PM »

We have been using constant voltage of about 1.4, limiting the max amps to between C/10 and C/20. MAYBE C/6 for a cordless drill or something.

Some major retailer says boo-koo charges, if C/10 is not exceeded, and a float charge of C/20 does no harm.

No problems here. Except for 'AAAA' cells (7.2/9V), that seem to have a cell go reversed more than expected.

G-

willib · « **Reply #20 on:** June 07, 2006, 01:02:46 PM »

if you use thin enough wire , and use enough of it , i'm sure you could generate a kilovolt at very low current though

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Author Topic: Variable input using the LM317 regulator question... (Read 7711 times)