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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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 28 Aug 2004 5:54 2N3904 Transistor |
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Hi guys,
can anyone tell me wats the I_BL(Base Cutoff Current) in the datasheet of 2N3904 for? I'm not really good at reading the datasheet so I hv no idea on how to use it. I try driving 10mA into the base of this transistor and it works but then I'm scared that I might ruin this transistor becoz I read that the I_BL can only be a maximum of 50nA only!!!???
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House_Cat
Joined: 21 Feb 2002
Posts: 1392
Helped: 292
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| 28 Aug 2004 6:50 Re: 2N3904 Transistor |
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When a junction transistor is cut off, the base emitter junction is reverse biased. Ibl is leakage current that is flowing in the reverse biased base emitter junction - you can't "drive it" with 10ma in the reverse direction unless you have high enough base-emitter voltage to permanently break down the junction.
The Ibl value is given so you can compute what value resistor to use to bleed the leakage current off, or what leakage current to plan on in direct coupled circuits.
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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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| 28 Aug 2004 10:19 2N3904 Transistor |
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| How can I use the 2N3904 transistor to amplify the current? Can anyone give me an example?
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echo47
Joined: 07 Apr 2002
Posts: 4205
Helped: 565
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| 28 Aug 2004 10:58 Re: 2N3904 Transistor |
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| ericmar wrote: |
| How can I use the 2N3904 transistor to amplify the current? Can anyone give me an example? |
Current Gain is the fundamental behavior of a transistor (assuming you have biased it into linear operation):
Collector current equals Base current times transistor's Beta.
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House_Cat
Joined: 21 Feb 2002
Posts: 1392
Helped: 292
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| 28 Aug 2004 22:49 Re: 2N3904 Transistor |
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| How can I use the 2N3904 transistor to amplify the current? Can anyone give me an example? |
You need to explain exactly what you are trying to do. Your question indicates that you don't have a clear understanding of the behavior of voltage and current (Ohm's law for starters).
Current is dependent on the load impedance. You don't just put some current into a device like a transistor, and then get some greater current out. The transistor must be driving some load - what is that load? What are you trying to do? Is the load purely resistive, or is it a relay coil, filter, resonant circuit, small motor, LED, speaker, etc.
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 29 Aug 2004 5:31 2N3904 Transistor |
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Someone above fundamental part of transistors in current amplification. BJT are great for current amplification but fundamental for all transistors (not only BJTs) are "switching properties".
2N3904 is NPN BJT.
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ericmar
Joined: 14 Apr 2004
Posts: 279
Location: Singapore
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| 29 Aug 2004 13:06 Re: 2N3904 Transistor |
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| House_Cat wrote: |
| Quote: |
| How can I use the 2N3904 transistor to amplify the current? Can anyone give me an example? |
You need to explain exactly what you are trying to do. Your question indicates that you don't have a clear understanding of the behavior of voltage and current (Ohm's law for starters).
Current is dependent on the load impedance. You don't just put some current into a device like a transistor, and then get some greater current out. The transistor must be driving some load - what is that load? What are you trying to do? Is the load purely resistive, or is it a relay coil, filter, resonant circuit, small motor, LED, speaker, etc. |
Let's say I want to amplify the output signal (a,b,...,g) of SN74LS48 as in this circuit. How should I use the transistor?
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House_Cat
Joined: 21 Feb 2002
Posts: 1392
Helped: 292
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| 29 Aug 2004 22:11 Re: 2N3904 Transistor |
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You could just use three more 74LS48's, since each is intended to drive one 7 segment display.
I haven't run any numbers to verify values; however, something like the illustration below should work too. I've only illustrated one segment, you would use the same circuit on each segment line.
The transistors have to either be used in emitter follower configuration, or you'll have to use two transistors to get a non-inverting stage to drive the LED segment.
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Kevin Weddle
Joined: 10 Jul 2004
Posts: 101
Location: San Antonio, TX
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| 30 Aug 2004 17:29 Re: 2N3904 Transistor |
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| If you are just learning, you will no doubt fry a couple of transistors. Here's a hint : Current times voltage of the transistor is equal to the power.
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