Stupid Question reguarding Transistor

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Kagetsuki
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Posted by Kagetsuki: Sun. May 20, 2007 - 09:16 PM
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So I have these transistors labeled C1815, they are NPN and apparently audio transistors. I grabbed the data sheet on them here: http://www.datasheetcatalog.com/...

So, I've never used "audio" transistors that I knew of until now, so maybe I'm just not aware of how they function as opposed to normal transistors, but it doesn't seem to be functioning as any transistor I'm familiar with (not many). After having problems with it, I hooked it up to a simple LED/resistor circuit to test it out. I turned out the circuit without anything connected to the base of the transistor and the LED turned on. So with absolutely nothing on the base I have current flowing through the transistor. When I attach a line to the base I get no visible change. I'd love to read out voltage/amperage but I don't have a multimeter (I live in Japan, and am currently on a long vacation in America, and have no descent parts shop near me so I grabbed what I could and am waiting on a digikey order with amongst other things a multimeter).

So, what did I do wrong? Please tell me how inexperienced and foolish I am for not understanding this and show me how I can be less uninformed about transistors in the future.

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Learning and Information, General Electronics
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digitool
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Posted by digitool: Sun. May 20, 2007 - 10:27 PM
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Just a wild guess but i would look at the ordering of the pins.Most that I have seen have the base as the center but it looks like the base is the last pin.

Google "testing transistors" and some of the sites show how to test using a multimeter.I just did this myself for a simple RS232 to 3.3V circuit (I wasn't that up on them either and needed how to tell a PNP from a NPN).

Pete

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bobgardner
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Posted by bobgardner: Mon. May 21, 2007 - 04:01 AM
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The pins are 1-2-3 Emitter-Collector-Base. Put the red probe on the base.... on the rx1 scale read 'something' like 500 ohms to the other pins... with black on the base should read 'nothing' (infinity) to the other pins... B to E tests like a diode and B to C test like a diode.

Imagecraft compiler user

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leon_heller
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Posted by leon_heller: Mon. May 21, 2007 - 09:46 AM
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"Audio transistors" are typically low-noise devices. They work the same way as any other BJTs.

Leon

Leon Heller G1HSM

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Kagetsuki
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Posted by Kagetsuki: Mon. May 21, 2007 - 03:05 PM
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leon_heller wrote:
"Audio transistors" are typically low-noise devices. They work the same way as any other BJTs.

Leon

I had thought something like that but the apparently strange behavior made me think twice. Thanks!

Perhaps a stupid follow up question: Are there any down sides to using audio transistors vs. higher noise transistors?

Digitool and Bobgardner: Thanks! I used your suggestions to find the orientation of the transistor. I ignored the data sheet, and started testing the transistor in a variety of pin configurations. In the end I found the configuration of the pins (which was EBC), which definitely is not what was written on that data sheet and is simply the opposite of what I am used to.

Thinking now, the multimeter I have back in Japan has a transistor tester that I have never used. That would have come in handy.

So, thanks everybody!

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leon_heller
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Posted by leon_heller: Mon. May 21, 2007 - 05:41 PM
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Kagetsuki wrote:
leon_heller wrote:
"Audio transistors" are typically low-noise devices. They work the same way as any other BJTs.

Leon

I had thought something like that but the apparently strange behavior made me think twice. Thanks!

Perhaps a stupid follow up question: Are there any down sides to using audio transistors vs. higher noise transistors?

Not really, they tend to be more expensive than general-purpose devices like the 2N3904.

Leon

Leon Heller G1HSM

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wangdong8311
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Posted by wangdong8311: Thu. May 31, 2007 - 08:40 AM
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sososo

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