Practical Electronics/Bipolar Transistors/NPN Transistor

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NPN Transistor

NPN Transistor is made by joining one Positive-Typed Semiconductor in between two Negative-Typed Semiconductor . A Semi Conductor device that has three legs Base , Colletor and Emitter forming a bi junction namely BE and BC junctions

NPN Transistor has the symbol with emitter leg has arrow points out

Transistor Biasing

4R Configuration

V_{B}=V_{i}{\frac {R_{2}}{R_{2}+R_{1}}}

V_{E}=V_{B}-0.7=V_{B}

I_{E}={\frac {V_{E}}{R_{4}}}={\frac {V_{B}}{R_{4}}}

I_{C}=I_{E}

V_{C}=I_{C}R_{4}

V_{C}=V_{i}(1-{\frac {R_{3}}{R_{4}}}{\frac {R_{2}}{R_{2}+R_{1}}})

When choosing the resistor's value R₂ >> R₁ or R₁ = 0, the formula above is reduce to

{\frac {V_{o}}{V_{i}}}=(1-{\frac {R_{3}}{R_{4}}})

Choosing resistor's value

R₃ = 0 . V_o = V_i . Transistor is a Non-Inverting Buffer or non Inverting Voltage Follower

R₃ = 2R₄ . V_o = -V_i . Transistor is an Inverting Buffer or Inverting Voltage Follower

R₃ = nR₄ . V_o = -(n-1)V_i . Transistor is an Inverting Amplifier

When choosing the resistor's value R₄ = R₃ the formula above is reduced to

{\frac {V_{o}}{V_{i}}}=1-{\frac {R_{2}}{R_{2}+R_{1}}}

Choosing resistor's value

R₂ = 0 or R₂ >> R₁. V_o = V_i . Transistor is saturated or fully on, correspond to state 1 logic

R₁ = 0 . V_o = 0 . Transistor is in cut off mode fully off, correspond to state 0 logic

2R Configuration

Without the biasing resistor network at the base

${\frac {V_{o}}{V_{i}}}=1-{\frac {R_{3}}{R_{4}}}$

Choosing resistor's value

R₃ = 0 . V_o = V_i . Transistor is a Non-Inverting Buffer or non Inverting Voltage Follower

R₃ = 2R₄ . V_o = -V_i . Transistor is an Inverting Buffer or Inverting Voltage Follower

R₃ = nR₄ . V_o = -(n-1)V_i . Transistor is an Inverting Amplifier

Transistor's Rectifier

With AC Signal or AC Voltage and transistor conducts current . The NPN transistor will pass positive half-cycle AC Voltage or Signal and ground the negative half-cycle

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