I've gone mad. npn question.

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KamPutty
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I've gone mad. npn question.

Post by KamPutty » Thu Mar 23, 2006 11:20 am

Hi all!

I've gone mad.

Said that...

I'm trying to send 350mA thru this npn

link to npn

I send 317mA into (C)
I get 60mA from (E)

From the specs, I thought it could handle that voltage...

Have I gone mad?!

~Kam (^8*

JPKNHTP
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Re: I've gone mad. npn question.

Post by JPKNHTP » Thu Mar 23, 2006 11:34 am

-JPKNHTP
-God Bless

KamPutty
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Re: I've gone mad. npn question.

Post by KamPutty » Thu Mar 23, 2006 11:58 am

JPKNHTP,

Thanks for the reply. To be totally honest, I'm not sure I understand...

why am I not getting the same voltage from whats being pushed into the Collector, and whats being sent from the Emittor?

~Kam (^8*

Ron H
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Re: I've gone mad. npn question.

Post by Ron H » Thu Mar 23, 2006 12:29 pm

JPKNHTP, that's nice way to let the magic smoke out of the PNP. You need some base current limiting.
Kam, the collector is not generally used as an input on a transistor. Can you post a schematic of what you are trying to do?

JPKNHTP
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Re: I've gone mad. npn question.

Post by JPKNHTP » Thu Mar 23, 2006 2:19 pm

-JPKNHTP
-God Bless

Robert Reed
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Re: I've gone mad. npn question.

Post by Robert Reed » Thu Mar 23, 2006 4:09 pm

Kam
Have no idea what your "pushing " and "sending" mean, but if you are trying to use this transistor as a swittch--and you are inquiring why the collector and emitter do not show the same voltage, this might help: first off they never will show the same voltage, but when driven heavily into saturation you can approach 0.1 volts differential. If this is what your post is about, then you need more base drive current to attain this. Of coarse this assumes the transistor can handle the load current

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Edd
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Re: I've gone mad. npn question.

Post by Edd » Thu Mar 23, 2006 4:26 pm

Also standing by … :D

KamPutty
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Re: I've gone mad. npn question.

Post by KamPutty » Thu Mar 23, 2006 6:39 pm

sorry for the delay!

I have a LED that I want to light.

Here is my setup (LED side)

+6v --> LED +
Gnd --> res 7.5 ohm --> npn Collector
npn Emittor --> LED -
npn Base --> res 10k --> pic pin

I can toggle the LED just fine.

If I put my meter on npn Collector and +6v, I get 317mA

If I put my meter on npn Emittor and +6v, I get 60mA.

the only part between the two is the npn. Said that, why 60mA's?

~Kam (^8*

KamPutty
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Re: I've gone mad. npn question.

Post by KamPutty » Thu Mar 23, 2006 6:49 pm

ooops, error


+6v --> LED +
Gnd --> res 7.5 ohm --> npn Emittor
npn Collector --> LED -
npn Base --> res 10k --> pic pin

If I put my meter on npn Emittor and +6v, I get 317mA

If I put my meter on npn Collector and +6v, I get 60mA.
~Kam (^8*

dyarker
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Re: I've gone mad. npn question.

Post by dyarker » Thu Mar 23, 2006 7:46 pm

In current measuring mode a meter has very low resistance. When you put the meter to emitter and +6V you are shorting around the LED and transistor, and measuring current resulting from 6V across 7.5 Ohm.

To measure emitter current, disconnect 7.5 Ohm resistor from emitter, put one meter lead on open resistor lead and other meter lead on emitter. Similar to measure collecter current.

Current is always measured with meter in series with the current path.

You didn't say what kind of LED, but 7.5 Ohms sounds too low, try around 220 Ohm. The 10K base resistor is too high to saturate the transistor.

Gota' get ready for work, maybe more later if someone else hasn't helped more by then.

Cheers,
Dale Y

positronicle
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Re: I've gone mad. npn question.

Post by positronicle » Thu Mar 23, 2006 7:46 pm

--Edited by Positronicle--

JPKNHTP
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Re: I've gone mad. npn question.

Post by JPKNHTP » Thu Mar 23, 2006 8:06 pm

-JPKNHTP
-God Bless

positronicle
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Re: I've gone mad. npn question.

Post by positronicle » Thu Mar 23, 2006 8:32 pm

--Edited by Positronicle--

JPKNHTP
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Re: I've gone mad. npn question.

Post by JPKNHTP » Thu Mar 23, 2006 8:41 pm

-JPKNHTP
-God Bless

KamPutty
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Re: I've gone mad. npn question.

Post by KamPutty » Thu Mar 23, 2006 8:58 pm

Hi all,

thanks for the replys....

LED specs:

3.99v/350mA max rating. (1 watt LED)

I am going to use [email protected]

This is how I derived the 7.5

res=(6v - 3.5) / .330 = 7.58 ohm, 0.825 watts

I am using a 1 watt resister.

About the Base, it seems to be working, I'm not sure I fully understand the issue about Saturating or lack off.

BTW, thanks for all the help! I've nearly blinded myself a few times with this LED! It's a bright guy! I mean <BRIGHT>, spotlight bright! WOW!

~Kam (^8*

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