1. BJT, Bipolar Junction Transisor
Base Current
Controls
Output current
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2. AGENDA BJT transistorman Transistor types Bipolar Junction Transistor
BJT models
parameters
water model
NPN and PNP
operation modes
switch open
switch closed
BJT
linear, controlled current source
active operation
characteristics
DC input characteristics
ac input characteristics
BJT DC biasing circuits
base bias
base bias + collector feedback
base bias + emitter feedback
voltage divider
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3. BJT, transistor man
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4. Transistor Types Output current controlled by input current BJT =
Bipolar Junction Transistor
FET =
Field Effect Transistor
Output current controlled
by input voltage
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5. BJT, Bipolar Junction Transisor
Transistor = Transfer Resistor
BE Forward bias, BC Reverse bias
So low ohmic high ohmic
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6. BJT, Bipolar Junction Transisor
Emitter = Sent electrons
Base = Base
Collector = Get electrons
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7. BJT, Models
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8. BJT, parameters
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9. BJT, Water model
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10. BJT, Water model
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11. BJT, NPN and PNP
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12. BJT, Operation modes Cut-off and saturation; BJT is used as a switch
Active operation
Quiecent Point;
BJT is used as a
controlled
current source,
or analog amplifier
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13. BJT, Switch open
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14. BJT, Switch closed
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15. BJT, Lineair, controlled current source
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16. BJT, active operation
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17. BJT, characteristics DC model ac model
DC model; Vbe = 0V Ube, Uce, Ic, Ib, Ie Capitals
ac model; re = 26mV/Ie ube, uce, ic, ib, ie Low cases
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18. BJT, DC input characteristics
Vbe = 0V7
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19. BJT, AC input characteristics
re = 26mV/Ic
The dynamic resistor can be
calculated by the DC current Ic
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20. BJT, characteristics
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21. BJT, DC biasing circuits
A base bias
B base bias + emitter feedback
C base bias + collector feedback
D voltage divider
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22. BJT, base bias, introduction
Base current determined by Vcc, Rb and Vbe
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23. BJT, base bias Calculate Ib and then Ic
Ic directly dependent on ß variation
So, for stability a “bad” circuit
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24. BJT, base bias load line Q-point = Quiecient point = Working point
Load line is the loading of the transistor seen from Uce (>0V7)
Vcc and Rc determines the;
“open voltage” and the “short circuit current”
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25. BJT, base bias load line Reliable circuit = Q-point stability
Load line is the loading of the transistor seen from Uce (>0V7)
Vcc and Rc determines the;
“open voltage” and the “short circuit current”
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26. BJT, base bias load line Vce always > 0V7 BC junction REVERSE
If Rc too big, transistor in saturation;
then;
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27. BJT, base bias load line Vce always > 0V7 BC junction REVERSE
If Vcc too small, transistor in saturation;
then;
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28. BJT, base bias example Calculate; Ib, Ic URc, Uc, Uce
Draw output caracteristic
Calculate now;
Uce if ß = 40
How many % did Uce Change
Ib = 47 uA, Ic = 2,35 mA,
URc = 5,17 V, Uc = 6,83 V, Uce = 6,83 V
Uce (for ß = 40) = 7,86 Ξ 15 %
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29. BJT, base bias example Ib = 33 uA, Ic = 2,9 mA URc = 7,9 V, Uc = 8,1 V
Rb = 282,5 kΩ, Ic = 3,2 mA,
Rc = 1,855 kΩ
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30. BJT, base bias example ß = 200, VRc = 8,8 V Vcc = 16 VRb = 765 kΩ
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31. BJT, base bias + emitter feedback
Base current determined by Vcc, Rb, Vbe and Ve
More stable for ß variations, than base bias.
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32. BJT, base bias + emitter feedback
Always calculate in the smallest current Ib !!
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33. BJT, base bias + emitter feedback
Load line is the loading of the transistor seen from Uce (>0V7)
Vcc, Rc and Re determines the;
“open voltage” and the “short circuit current”
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34. BJT, base bias + emitter feedback example
Calculate;
Ib, Ic
URc, Uc, Ue, Uce
Draw output caracteristic
Ib = 6,2 uA, Ic = 0,74 mA,
URc = 8,9 V, Uc = 7,1 V, Ue =-0,9 V, Uce = 8,0 V
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35. BJT, base bias + emitter feedback example
Calculate;
Ib, Ie
URe, Ue, Uce
Draw output caracteristic
Ib = 24 uA, Ie = 2,9 mA,
URc = 3,5 V, Ue = -2,5 V, Uce = 2,5 V
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36. BJT, base bias + collector/emitter feedback
If Ic >
then Uc <
then Ib <
If Ic >
then Uc <
and Ue >
then Ib <
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37. BJT, base bias + collector feedback
Always calculate in the smallest current Ib !!
The current through Rc is not Ic but Ic + Ib,
so (β+1)Ib !!!
If Ic rises for any reason, then Uc falls and
also Ib decreases, so then Ic decreases
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38. BJT, base bias collector feedback example
Calculate;
Ib, ß, Ic
Draw output caracteristic
Ib = 13 uA, ß = 196, Ic = 2,5 mA
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39. BJT, base bias collector/emitter feedback
Always calculate in the smallest current Ib !!
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40. BJT, base bias collector/emitter feedback ex
Calculate;
Ib, Ie
URc, Uc, Ue, Uce
Draw output caracteristic
Ib = 11,8 uA, Ie = 1,1 mA
URc = 5,2 V, Uc = 4,8 V
Ue = 1,3 V, Uce = 3,5 V
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41. BJT, voltage divider Vb is a stable voltage - 0,7 V =
so Ve is a stable voltage
Ie is determined by Ve/ Re
Ic = Ie . ß/(ß+1)
Ic is very stable and nearly independent to ß variation, as long as ß is BIG in value
2 methods of calculating Ic
- neglegting Ib, use voltage divider
- not neglecting Ib and use thevenin
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42. BJT, voltage divider, neglect Ib
So neglegt Ib to R2,
or in general Ri >> R2
In practice 10 times bigger
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43. BJT, voltage divider, exact, thevenin
Thevenin resistance
R1 // R2
62k // 9k1= 7k9
Thevenin voltage
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44. BJT, voltage divider, exact, thevenin
7k9
2V0
Ib = 20 uA
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45. BJT, voltage divider, example
Thevenin resistance = 6k8
Thevenin voltage = 3V1
Ib = 18,8 uA
Ic = 2,25 mA
re = 11,5 Ω
URc = 7V4
Uc = 10V6
Ue = 2V3
Uce = 5V1
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46. BJT, voltage divider, example
Thevenin resistance = 255k
Thevenin voltage = 0V0
Ib = 14,3 uA
Ic = 1,9 mA
re = 14 Ω
URc = 17V3
Uc = 0V7
Ue = -3V7
Uce = 4V4
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47. BJT
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48. BJT
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