Q.  Ghania is attempting to design a shunt regulator, of approximately 20V, for her sister Azka's toy. Two types of zener diodes are there: 6.8V devices with r_z 10 W and 5.1V devices with r_z 30 Ω. For the two alternates possible, determine load regulation. In this calculation ignore the effect of regulator resistance R.

Solution:

Alternates

a). So as to make up 20V using 6.8V zener, three diodes will be required, thus 3x6.8=20.4V, so is the resistance, 3x10=30 Ω.

Thus load regulation, ignoring load resistance = -30 Ω.

b). 4 diodes of 5.1 will create 20.4 volts, thus 4x5.1=20.4V, so is the resistance of the zener i.e.

                                                                                4x30=120Ω.

Load regulation (ignoring R) = -120 Ω