Transistors

Discussion in 'Embedded Systems and Microcontrollers' started by iPromise, Aug 11, 2013.

1. iPromise Thread Starter New Member

Aug 11, 2013
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I read that Transistors amplify the voltage from input.

But how does amplifying voltage help create logic gates preforming operations (AND gate, OR gate, XOR gate, NAND, etc.)?

2. tracecom AAC Fanatic!

Apr 16, 2010
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Transistors also function as switches, and it is in that mode that they may be arranged as logic gates. See two examples attached.

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3. iPromise Thread Starter New Member

Aug 11, 2013
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Thanks for the quick and clear answer!

I'm beginning to love this forum.

Jul 18, 2013
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A bi-polar transistor is considered a current amplifier, a FET could be considered a voltage amplifier.
Max.

5. onlyvinod56 Senior Member

Oct 14, 2008
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1
consider an npn CE mode. if a relay coil is connected between collector and Vcc.

the collector current Ic = (Vcc - Vce)/R.relay.
How can the BJT amplifies the current as already the current is decided by the relay coil resistance??

6. ScottWang Moderator

Aug 23, 2012
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The normally BJT amplifies the current is working in the linear area, the Ic is depends on the Ib and count on hfe=Ic/Ib, and as you said to used the relay that is working in the logical area, hfe=Ic/Ib=10 for Vce saturation.

7. jegues Well-Known Member

Sep 13, 2010
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BJTs are often described as both a current controlled and voltage controlled current sources, but under varying circumstances.

The current control model, $I_{C} = h_{FE}I_{B}$ is often used when we are in the linear region of operation, as this is "good enough."

However, other models like the Eber-Molls model, $I_{C} = I_{S} \left(e^{\frac{V_{BE}}{V_{T}}}-1 \right)$ are used to address the fact that transistors are indeed transconductance devices, meaning that the collector current is determined by its base-to-emitter voltage.

Last edited: Nov 14, 2013