LM339 Voltage Comparitor Question

[JumperWire]

Greetings to all,

I am new to this forum and somewhat new to electronic circuits so please excuse my ignorance but I'm trying.

I am using an LM339 with a phototransistor to drive a PNP3906 tranistor that triggers a 12 volt relay. I am only using one set of inputs and one output so my question is; do I have to tie down the unused inputs and outputs of the LM339 or can they be left floating?

Would appreciate any help from those of you more knowledgable than me, which is probably every member of this fourm.

 

[crutschow]

It's always good form to tie down unused input (not necessarily unused outputs) but that shouldn't be critical for the LM339. It is a must for all MOS and CMOS circuits, however.

 

[audioguru]

An LM393 is a dual version of the ML339 quad comparitor IC that is in an 8-pins case.

 

[shortbus=]

You also need a pull-up resistor to V+ on the out put of the comparator. It sinks current only, does not out-put current. Check the data sheet for values.

 

[JumperWire]

I had a suspicion that might be the case although I couldn't confirm it but now you have. Thanks for the help!

Jack

 

[JumperWire]

Thanks for the info Uncle Scrooge. I knew of the LM393 but just happened to have an LM 339 laying around and wanted to breadboard the circuit and make sure it's going to work. I'll go with an LM 393 for the actual circuit to conserve board space.

 

[JumperWire]

Thanks for the tip shortbus. I will check the data sheet.

Everyone has been very helpful in this forum. I'm glad I joined...

 

[shortbus=]

Thanks for the tip shortbus. I will check the data sheet.

Everyone has been very helpful in this forum. I'm glad I joined...

Your welcome, Google and data sheets are your best fiends! Just Googleing a part number is usually a great place to start.

 

[audioguru]

I get datasheets from www.datasheetarchive.com where I can see many different manufacturers datasheets for the same part.
Sometimes a manufacturer copies somebody elses part and does not print all the details in their datasheet. So I usually pick the datasheet with the most number of pages.

 

[JumperWire]

I tried to find an anwser to my original question on Google with no luck. But then, Google brought me to this forum where I did get my anwser. So, you are right. Google is my best friend. Now, onto those data sheets...

 

[JumperWire]

Again, thanks for the tip and the link Uncle $crooge. I know it will be useful in the future and it makes sense that the datasheet that reads like a laundry list will have the most info in it.
By the way, how are your three nephews doing these days?

 

[audioguru]

By the way, how are your three nephews doing these days?

I actually have 3 nephews who are all over the world and are fine. 2 are engineers and the 3rd one might become an engineer.
The cartoon ones are getting old like me.

 

[Roff]

2 are engineers and the 3rd one might become an engineer.

I'm sorry to hear that.
There's still hope for the 3rd one.

 

[audioguru]

Haven't we all seen people who hated their jobs? I was happy in my job and had a great time. I hope my nephews also have a great time.

 

[Roff]

Haven't we all seen people who hated their jobs? I was happy in my job and had a great time. I hope my nephews also have a great time.

I didn't hate my job, either. Most of the time, I actually enjoyed it. But I've heard from a lot of engineers who were not as fortunate as you and I.
I also hope your nephews are fulfilled by their careers.

Especially Dewey.

 

[JumperWire]

Gentlemen, it doesn't matter if you are an engineer or if you shine shoes. What is important is that you are happy at what you do. I know people who have what I would consider a great job but hate it. A lot of this is atitude of course. So either enjoy what you do and make a difference or find something else to do that will make you happy. It beats being miserable for your entire career.

Dewey? I thought Louie was the hold out.

Jack

 

[JumperWire]

Hey, two out of three ain't bad Uncle $crooge. I'd be willing to bet the third nephew follow suit though. At the end of the day he won't want to be out done by the others.

Yes, Huey, Dewey and Louie must be getting close to Medicare by now I would have to assume...

 

[audioguru]

I am also enjoying retirement. I get a senior's discount almost everywhere I go. My government takes good care of me.

 

[Roff]

So either enjoy what you do and make a difference or find something else to do that will make you happy. It beats being miserable for your entire career.

I agree with the sentiment, but it is simplistic, unless you have no family obligations.

Anything else you want to know about comparators?

 

[JumperWire]

You are a lucky duck, Uncle $crooge...a lucky duck indeed.