Problem-2 [150]

In the figure shown below, the transistor T, is used as a switch for the load resistance

R₁.

The circuit data are the following: the voltage of the main de source,Vcc= 200.006/V/;

the voltage of the base de source, V₁= 3.5 /V/; the load resistance, R₁= 1.98006 /2/; and

the resistance of the base circuit, RB = 0.0625 /22/.

V₂

RB is

BE

ic

(6)

ACE

Re

+

Vcc

1/nComments:

The values shown for the main de voltage source and the load resistance do not look

too realistic. The reason is to have the data of the shown circuit in agreement with

the waveforms that follow.

The switch is shown on the base circuit to model the control process that is present

on the base circuit.

For a cycle of the transistor operation, the waveforms for different quantities are

shown in the attached Figure 8-10. The length of different time intervals shown in

the figure is as follows:

ta = 0.5 /μs/;

t₁= 1 /µs/;

ts = 5 /µs/;

tf = 3 /us/.

It is also specified that the signal frequency is fs= 10 /kHz/ and that the duty cycle is

D = 50% (Here the duty cycle is defined as the ratio of the time length along which

the base signal is present to the total time length of a cycle. With the data shown in

Figure 8-10, the duty cycle is represented as: D /%/= ((ton+ tn)/T) x 100)./n200/vl

2/V] =VCE(sat)

1001A=Ics

3/MA/= ICEO

·0

8/A/= ¹8s

-3/V/ = V₁E(San

counted

as t=0

karte &

H.

ig

1

VBE

tn

1

+-+-+-

•T = 1/₂

to

Figure 8-10 Waveforms of transient switch./nFor the given circuit and its operation, calculate the value of:

a) The energy consumed (lost) within the transistor, due to the collector current

during the initial turn-on time-interval, that is, for 0 ≤t≤ta.

b) The same quantity as in a) during the final turn-on time-interval, that is,

for ta ≤ t ≤ton.

c) The same quantity as in a) during the full conduction time-interval, that is, for

ton ≤ t ≤ (ton + tn + ts).

d) The same quantity as in a) during the initial turn-off time-interval, that is, for

(ton + tn + ts) ≤t≤ (ton + tn + toff).

e) The same quantity as on a) during the full turn-off time interval, that is, for

(ton + tn + toff) ≤ t ≤ T.

f) The total energy and the corresponding average power consumed (lost) within

the transistor along an operation cycle, due to the collector current.

g) The energy and the corresponding average power supplied by the base voltage

source VB along an operating cycle. These correspond to the energy and the

average power consumed (lost) within the transistor and in the base circuit

resistance, R₁.

h) The total energy and the corresponding average power consumed (lost) per

transistor, that is, due by both the collector and the base current, including the

energy and the corresponding average power lost in the base circuit resistance

Rb./nj)

i) For one cycle, the total energy and the corresponding average power supplied

to the circuit by the main voltage source, Vcc and by the base voltage source VB.

For one cycle calculate the total energy and the corresponding average power

consumed by the load resistance R₁. For this purpose, you must use the load

resistance R₁'s value and the corresponding collector current.

k) Calculate the following difference: (total energy defined in (i)) minus (total

energy defined in (h)). The same difference can be defined by using the

corresponding average powers.

Compare the difference obtained here with the values obtained in (j).

1) The circuit efficiency in percent, counting the total energy or the corresponding

average power supplied by both, the main and the base de source, and the total

energy or the corresponding average power lost in the transistor and in the

base power resistance Rp.

For the same purpose, it can be counted the total energy or the corresponding

average power supplied by the main and base de sources and the total energy

or the corresponding average power absorbed by the load resistance R₁.

m) Along an operation cycle, plot the instantaneous power carried by the

transistor, counting only the collector current. On the graph clearly specify the

value for the maximum and minimum value of the instaneous power and the

corresponding moment in time when each of these is reached.