1 emitter collector base npn bipolar transistor The Transistor as a ...
The Transistor as a voltage-controlled resister control knob
npn bipolar transistor collector base
current out emitter
2N2222 ebc 6.071 Bipolar Transistors, Spring 2002
current in 1
1
The Diode
I(A)
0.6V
V (volts)
As described, but turns on at 0.6V (for a Si diode).
6.071 Bipolar Transistors, Spring 2002
2
2
collector
Transistor Properties
base
emitter
IC = bI B I E = IC + I B = (1 + b )I B VBE = VB - VE = +0.6V Normally off (base/emitter reverse biased), small input current and voltage relative to emitter turns it on, switching and amplifying 6.071 Bipolar Transistors, Spring 2002
b ~ 100, but changes with temperature and with VCE
3
3
VCC
Transistor Switch collector current depends on the voltage drop across the bulb.
R
IC @ bI B
on off 10 kW
IB =
6.071 Bipolar Transistors, Spring 2002
VCC - VBE R
since the transistor state depends on the base current, leaving the base open circuited would eventually shut down the transistor, but this is sloppy. 4
4
Transistor Switch
IB
VCC
VCC = IR + VBE
R
VCC - VBE R V -V IC = b Ê CC BE ˆ Ë ¯ R
IB = VBE
†
6.071 Bipolar Transistors, Spring 2002
VBE = 0.6V
5
†
5
Emitter Follows as a Current Source #1 +10V +10V
Vin Vin
load
1kW -10V
1kW
-10V What is Vout?
Vout = Vin - 0.6V If the base/emitter is forward biased
6.071 Bipolar Transistors, Spring 2002
6
6
Emitter Follows as a Current Source #2 What is Vout when the transistor is off?
+10V
+10V
high impedance
fi
Vin 1kW
1kW 1kW
-10V
6.071 Bipolar Transistors, Spring 2002
-10V
-5V
fi 1kW 1kW
1kW
-10V
7
7
Emitter Follows as a Current Source #3 At what base voltage does it turn off? +10V
VBE = 0.6V \Vin = -4.4V
Vin 1kW 1kW -10V
6.071 Bipolar Transistors, Spring 2002
8
8
Emitter Follows as a Current Source #4 +10V +10V
Vin Vin
-10V
1kW 1kW -10V
Vout
Vin
Ï V - 0.6V; Vin ≥ -4.4V Vout = Ì in -5V; Vin < -4.4V Ó 6.071 Bipolar Transistors, Spring 2002
9
9
Biasing 1 Often signals are AC (or capacitively) coupled into amplifier stages. Note a single sided voltage supply can not amplify the negative inputs.
Vin
+VCC Vin R
Vout
VB 6.071 Bipolar Transistors, Spring 2002
Vout 10
10
Biasing 2 Solve this by adding a DC to the base to shift the signal so that there is no clipping and AC coupling the output.
VCC select VCC = 15V
R1
want R1 || R2
npn bipolar transistor collector base
current out emitter
2N2222 ebc 6.071 Bipolar Transistors, Spring 2002
current in 1
1
The Diode
I(A)
0.6V
V (volts)
As described, but turns on at 0.6V (for a Si diode).
6.071 Bipolar Transistors, Spring 2002
2
2
collector
Transistor Properties
base
emitter
IC = bI B I E = IC + I B = (1 + b )I B VBE = VB - VE = +0.6V Normally off (base/emitter reverse biased), small input current and voltage relative to emitter turns it on, switching and amplifying 6.071 Bipolar Transistors, Spring 2002
b ~ 100, but changes with temperature and with VCE
3
3
VCC
Transistor Switch collector current depends on the voltage drop across the bulb.
R
IC @ bI B
on off 10 kW
IB =
6.071 Bipolar Transistors, Spring 2002
VCC - VBE R
since the transistor state depends on the base current, leaving the base open circuited would eventually shut down the transistor, but this is sloppy. 4
4
Transistor Switch
IB
VCC
VCC = IR + VBE
R
VCC - VBE R V -V IC = b Ê CC BE ˆ Ë ¯ R
IB = VBE
†
6.071 Bipolar Transistors, Spring 2002
VBE = 0.6V
5
†
5
Emitter Follows as a Current Source #1 +10V +10V
Vin Vin
load
1kW -10V
1kW
-10V What is Vout?
Vout = Vin - 0.6V If the base/emitter is forward biased
6.071 Bipolar Transistors, Spring 2002
6
6
Emitter Follows as a Current Source #2 What is Vout when the transistor is off?
+10V
+10V
high impedance
fi
Vin 1kW
1kW 1kW
-10V
6.071 Bipolar Transistors, Spring 2002
-10V
-5V
fi 1kW 1kW
1kW
-10V
7
7
Emitter Follows as a Current Source #3 At what base voltage does it turn off? +10V
VBE = 0.6V \Vin = -4.4V
Vin 1kW 1kW -10V
6.071 Bipolar Transistors, Spring 2002
8
8
Emitter Follows as a Current Source #4 +10V +10V
Vin Vin
-10V
1kW 1kW -10V
Vout
Vin
Ï V - 0.6V; Vin ≥ -4.4V Vout = Ì in -5V; Vin < -4.4V Ó 6.071 Bipolar Transistors, Spring 2002
9
9
Biasing 1 Often signals are AC (or capacitively) coupled into amplifier stages. Note a single sided voltage supply can not amplify the negative inputs.
Vin
+VCC Vin R
Vout
VB 6.071 Bipolar Transistors, Spring 2002
Vout 10
10
Biasing 2 Solve this by adding a DC to the base to shift the signal so that there is no clipping and AC coupling the output.
VCC select VCC = 15V
R1
want R1 || R2
