# Electronic Principles Questions

1)

Figure 1 represents the equivalent circuit of a voltage regulator where an unregulated 12V source is used to provide a stabilised voltage Vout using an 8V zener diode.

Using Kirchhoff's voltage law and by writing the appropriate equations find:

i. The currents i2 & i3.

ii. The output voltage Vout.

iii. The power dissipated by the zener diode (resistor RZ).

2)

a p.d. of V is connected between terminals A and B of the network below-

For a frequency of 32.274861 kHz calculate :

a. The j notation impedance of the network.

b. The polar representation of the impedance in the form giving the answer as a positive angle.

c. The magnitude of the voltage across C2 and its phase relative to the supply voltage.

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#### Solution Preview

1) Figure 1 represents the equivalent circuit of a voltage regulator where an unregulated 12V source is used to provide a stabilised voltage Vout using an 8V zener diode.

Using Kirchhoff's voltage law and by writing the appropriate equations find:

i. The currents i2 & i3.

ii. The output voltage Vout.

iii. The power dissipated by the zener diode (resistor RZ).

Solution: Kirchhoff's voltage law (or loop law) states: Algebraic sum of the potentials across various circuit elements in a loop is zero.

Kirchhoff's current law (or junction law) states: Algebraic sum of all the currents meeting at a junction is zero.

Various steps to be followed for writing the loop equation are as follows:

1. Designate currents in various branches of the given circuit as i1, i2, etc, assuming any suitable direction (strictly any arbitrary direction can be assumed; but most of the times the likely direction of current in a branch is apparent from the circuit configuration).

2. Mark the polarities across resistors (+, -) remembering that the current through a resistor flows from the higher polarity (+) towards the lower polarity (-). However, polarities of the two terminals of the battery remain as specified irrespective of the direction of current flow.

3. Write Kirchhoff's current equation for each junction in terms of i1, i2 etc. assuming a current flowing into the junction as +ve and a current flowing out of the junction as -ve and equate to zero (the choice of convention for +ve and -ve current is purely arbitrary).

4. Write Kirchhoff's voltage equation for each loop starting ...

#### Solution Summary

Electronic principles are examined. Equivalent circuits of a voltage regulator are determined.