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968 ⏐⏐⏐ TRANSFORMERS
insertion in a plastic bag could be a very dangerous proposition. If you
happen to break a bulb and get cut in the process, be sure to go right to
a medical facility since you could sustain fluorine or mercury poisoning.
21.15 COMPUTER ANALYSIS
PSpice
Transformer (Controlled Sources) The simple transformer configuration
of Fig. 21.50 will now be investigated using controlled
sources to mimic the behavior of the transformer as defined by its basic
voltage and current relationships.
+
Vg = 20 V ∠ 0°
–
R 1
10 �
Z i
+
1 : 4
E p E s R L 100 �
–
FIG. 21.50
Applying PSpice to a step-up transformer.
For comparison purposes, a theoretical solution of the network
would yield the following:
Zi � a 2 ZL 2 1
� � �� 100 �
4
� 6.25 �
(6.25 �)(20 V)
and Ep ��� �7.692 V
6.25 ��10 �
1 1
with Es � �Ep � � � (7.692 V) � 4(7.692 V) � 30.77 V
a (1/4)
and VL � Es � 30.77 V
For the ideal transformer, the secondary voltage is defined by Es �
Ns/Np(Ep) which is Es � 4Ep for the network of Fig. 21.50. The fact that
the magnitude of one voltage is controlled by another requires that we
use the Voltage-Controlled Voltage Source(VCVS) source in the
ANALOG library. It appears as E in the Parts List and has the format
appearing in Fig. 21.51. The sensing voltage is E1, and the controlled
voltage appears across the two terminals of the circular symbol for a
voltage source. Double-clicking on the source symbol will permit setting
the GAIN to 4 for this example. Note in Fig. 21.51 that the sensing
voltage is the primary voltage of the circuit of Fig. 21.50, and the
output voltage is connected directly to the load resistor RL. There is no
real problem making the necessary connections because of the format
of the E source.
The next step is to set up the current relationship for the transformer.
Since the magnitude of one current will be controlled by the magnitude
of another current in the same configuration, a Current-Controlled
+
–