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TOPIC: Who right

Re: Who right 7 years 7 months ago #10056

  • be80be
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Well for starters I did post my first circuit with any relay...

And what I did post used a buzzer to sound when dark and I just added a Led and resistor to the Thing to show how it works. Where and how the OP placed his relay is up to them.

The LM339 Is not able to source Power so the circuit is not easy to make work as is any way.

And I would of remove the part about a dang relay if I could but you post you can't change it after a minute or so now.

The reason being you have to set the resistor right to turn on and off the transistor.

Re: Who right 7 years 7 months ago #10057

  • Jon G
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Personally, I didn't see anyone say anything to the contrary in regard to suggestions, with the exception of using an NPN to source current... Which is why we are "here" by the way.

Are you saying that your drawing of the proves it works? I hope not.

What it looked like Jon was trying to discuss was the legitimacy of using an NPN to source current the way you suggested. At which point you became upset.

I personally would like some further explanation on the subject. If I can use an NPN to simply source current, that might cut my future transistor usage in half. Thanks.

Re: Who right 7 years 7 months ago #10058

  • jmessina
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You don't normally use an NPN switch to source current into an emitter load because in order to turn on the transistor you have to forward bias the base-emitter junction, so the voltage on the base has to be ~0.7V higher than what's on the emitter, otherwise the B-E junction isn't on.

In that thread, the little picture posted with 0.6V B-E shows that. It's just not showing you what the base voltage actually has to be to do that (+V + 0.6V).

Re: Who right 7 years 7 months ago #10059

  • Jon G
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So is the result this? http://en.wikipedia.org/wiki/Common_collector

Seems in line with what was described.

Re: Who right 7 years 7 months ago #10060

  • Jon Chandler
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Thank you Mike for providing the terminology - this circuit is called an emitter-follower and appears to be most commonly used as an amplifier for AC signals.

An in-depth explanation may be found in Introduction to Transistors, a presentation for Physics 275 at Ohio Wesleyan University. This presentation is pretty technical with all the nitty-gritty details.

This circuit may work well for some applications - just understand the details before soldering it together for maximum happiness.

Re: Who right 7 years 7 months ago #10061

  • Jon G
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Alright, since the topic is "Who right" Lets figure this out, because I'm still confused.

The circuit in question, posted by Burt:
http://digital-diy.com/forum/download/file.php?id=1928
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