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b.
(Block 6, continued from preced ing page)
IR will
as T A increases.
a. Decrease
GO TO BLOCK 12
b.
Increase
GO TO BLOCK 22
12
7
Refer to the text and return to BLOCK 22.
YOU ARE CORRECT!
A diode is rated at 500 mw at 25• C and
must be derated 3mw/" C. We wish to
operate the diode at 125• c . What is
Pd 1 max 1 at 125° C?
GO TO BLOCK 16
YOU ARE INCORRECT!
GO TO BL OCK 2
Refer to the text and return to BLOCK 6.
21
13
14
YOU ARE INCORREC T!
YOU ARE CORRECT!
VF will
as the ambient
temperature ( T A) increases .
a.
Decrease
GO TO BLOCK 6
b.
Increase
GO TO BLOCK 24
8
You have completed the test for the
second lesson. However, before going on
you should review any area in this lesson
you do not fully understand.
Bv
15
YOU ARE INCORREC T!
ARE CORRECT!
The current wh ich flows when a diode is
reverse biased is
a. IR
GO TO BL OCK 4
b.
IF
GO TO BLO CK 10
b
22
YOU ARE CORRECT!
As TA increases, Pd 1 max 1 - - - - -
Increases
GO TO BLOCK 13
b.
Decreases
GO TO BLOCK 7
a.
23
YOU ARE INCORRECT!
Refer to the text and return to BLOCK 1.
Refer to the text and return to BL OCK 4.
10
YOU ARE INCORRECT!
Refer to the text and return to block 21 .
11
YOU ARE CORREC T!
The forward
determ ined by
a.
voltage
drop ( VF)
is
RL
GO TO BLOCK 3
b.
IF
GO TO BLOCK 25
16 200 mw. If you do not have this result
your answer is incorrect. First check over
your arithmetic. Do not go on until you
obta in this correct answer.
GO TO BLOCK 8
20
24
YOU ARE INCORRECT!
Refer to the text and return to BLOCK 14.
25
YOU ARE CORRECT!
YOU ARE CORRECT!
The forward operating lim it of a diode is
a. Pd cmax 1
GO TO BLOCK 21
The reverse current ( IR) is determ in ed by
VR
GO TO BLOCK 14
a.
b.
RL
GO TO BL OCK 5
Colhtc rw
Lesson Three:
Collecror
Switching
This lesson is concerned with
switching , which is the basic
operation of digital circuits. A
transistor model is developed to
describe graphically the internal
operations of the transistor
switch.
Transistor model:
Rather than enter into a
lengthy discourse on semi-
conductor physics to describe
the operational characteristics of
transistors , we will in this lesson
develop a model from lessons one
and two. [Lesson one appeared in
the March 15, 1981 issue of PLAY
METER.] The model will behave
like a transistor but will be made
up of imaginary devices.
As shown in figure 3-1, there is a
diode between the emitter and the
base leads. This diode is referred
to as the base-emitter diode and
has the identical characteristics
of the diode in lesson two .
Between the emitter and collector
leads is a current generator which
produces a current [beta x Is].
where beta and Is hold the same
meaning as in lesson one .
10
Rc•
Referring back to lesson one ,
formula 4states :
Emiller
PNP Modt l
NPN Mode l
~
=
lc
Ia
F ig . 3· 1. Ope r1llone l mode/ a IOf both 1 NPN and 1 PNP ttM ·
ti iiOf. The C U H ~I gentriiOf ptociYCII I CUH.nt • • I . wMft
the dlodt I a fOfward bla t td .
solving for lc, we have :
lc
=
~ x
lc
Ia
ltc
flo
Therefore, the current produced
by the generator is the collector
current, lc. The dotted line
connecting the diode and gener-
ator indicates that the generator
is controlled by the diode . Since a
transistor is basically a resistive
device (the term transistor
derives from transfer resistor) , it
is represented as a resistor ,
collector to emitter AcE. The
value of resistance is determined
by the Ohm's Law value of the
voltage , collector to emitter and
I c.
[8)
RcE
VeE
lc
'"
F ig . 3-2 . An o peratl onl l model of • PNP trantlt tOf connec ted
Into • chc ull . Compare lh la circuli to the ont In Fi t . 1-5.
Tht model rtplacea tht PNP s ymbo l.
Operol •nlt
po1n1 of llt.
0
I
2
J
..
5
6
Vuho,lf!
Fi g. 3-3A. Tht opt re ti onal c hari Citrletlca of an open t witch.
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