Transistor Worksheet

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					Transistor Worksheet




         C
 B

          E
                                    Dual Subscripts




                                            C

                                B                Q1
                                                NPN

                                            E


When using dual subscripts, the first subscript represents where the (+) lead (red) on a
VOM would go, the second subscript represents where the black (-) lead would go. For
example, VAB is read as “What is the voltage at point A with respect to Point B?”


VE     VB      VC             VBE VEB VBC VCB VCE VEC


2V     2.7V    3V


5V     5.6V    12V


6.3V   7.0V    10V


3.8V   4.5V    12V
Now, a PNP transistor….

                                 C
                           B

                                 E

VE    VB     VC           VBE VEB VBC VCB VCE VEC

-3.8V -4.5V -12V


-1.2V -1.8V -15V


0V    -0.6V -10V


-1V   -1.6V -5V
                                      The Load Line


                 VCE




                                                                            IC

The load line for a circuit is drawn as follows:

   1. Determine the MAXIMUM voltage VCE across the transistor. This occurs when
      the transistor is OFF, and is equal to the source voltage at the collector (Vcc). Plot
      this on the „Y‟ axis.
   2. Determine the MAXIMUM current IC through the transistor. This occurs when
      the transistor is all the way ON (Saturated). Plot this on the X axis.
   3. Draw a straight line between the points defined above. This is the load line for the
      circuit, and describes the transistor‟s range of operation.

The Operating Point is plotted on the load line as follows:
   1. Calculate VCE and IC as done on the previous page.
   2. Plot the VCE on the Y axis and IC on the horizontal axis.
Draw lines straight up and straight across to intersect the load line at a point somewhere
between maximum current and maximum voltage. This is the operating point.
                    VCC




                          RC




                           Q1
                          NPN
        RB




Solution Method:

   1.   Assume VE = 0V
   2.   VB = VE + 0.7V
   3.   VRB = VCC – VB
   4.   IB = VRB / RB
   5.   IC = Beta x IB = IE
   6.   VRC = IC x RB
   7.   VQ = VCC – VRC
   8.   PQ = VQ x IC
Problems – Basic Circuit

VCC    RC     RB      BETA           VB     VRB     IB     IC    VRC   VCE   PQ

10V    1K     33K     20

12V    1K     33K     20

10V    1.5K   28K     15

12V    1.5K   36K     25

10V    0.7K   30K     22

Plot the load line and operating point for each problem above:
                                     Voltage Divider Bias

                   Vcc




 RB1                     Rc

                                         V out

                         Q1




RB2                      Re




Solution Method

1. VB = ((RB2)/(RB1+RB2)) x Vcc                     Voltage Divider Formula

2. VE= VB – 0.7                                     Diode Theory

3. IE = VE/RE                                       Ohm‟s Law

4. Ic = IE                                          Transistor Approximation

5. VRC = Ic x Rc                                    Ohm‟s Law

6. VQ = Vcc – VRC – VRE                             KVL

7. PQ = VQ x IE                                     Watt‟s Law

Problems for the circuit above:

RB1     RB2     RC            RE      VCC           VCE            IC          PQ

52K     10K     6.8K          2K      10V

60K     8K      6.5K          2.2K    10V

47K     12K     7K            3K      10V

50K     18K     6.8K          2K      12V

50K     8K      7K            1.8K    10V
Plot load lines and operating points for the above problems…
Testing Transistors



In order to verify that a transistor is good, use the following procedure:



For NPN transistors:

   1.   Place the RED ohmmeter lead at the base.
   2.   Place the BLACK lead at the emitter
   3.   Measure a LOW resistance.
   4.   Reverse the leads. Measure a HIGH resistance.
   5.   Place the RED lead again at the base.
   6.   Place the BLACK lead at the collector.
   7.   Measure a LOW resistance.
   8.   Reverse the leads.
   9.   Measure a HIGH resistance.

These will be the measurement(s) if the transistor is GOOD. Note that the device cannot
be in a circuit when this test is performed – the base must be lifted from the circuit to
avoid a parallel path, and of course power to the circuit must be OFF.


For PNP transistors:

   1.   Place the BLACK ohmmeter lead at the base.
   2.   Place the RED lead at the emitter
   3.   Measure a LOW resistance.
   4.   Reverse the leads. Measure a HIGH resistance.
   5.   Place the BLACK lead again at the base.
   6.   Place the RED lead at the collector.
   7.   Measure a LOW resistance.
   8.   Reverse the leads.
   9.   Measure a HIGH resistance.

These will be the measurement(s) if the transistor is GOOD. Note that the device cannot
be in a circuit when this test is performed – the leads must be lifted from the circuit to
avoid a parallel path, and of course power to the circuit must be OFF.
Term 2 Electronics Test                     Name :_______________________


For the following circuit:

   1. Given the following parameters, solve for the unknowns.

VCC = 12 V    RC = 3.3 K ohms      RB = 560K ohms Beta = 120




                      VCC




                             RC




                              Q1
                             NPN
       RB




VE = __________        VB = __________      VRB = __________    IB = __________



IC = __________        IE = __________      VRC = __________VCE (VQ) = _______
   2. For the circuit above, draw the load line and indicate the operating point.


             VCE




                                                                         IC




2. For the transistor below, label the terminals (emitter, collector, base) and indicate
   the type of transistor (PNP, NPN).

				
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posted:11/26/2011
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