diode is much larger than the load current. This is to have good load regulation. Choose Zener current as five times the load current, i.e., I Z = mA. The total current through R S is, therefore, mA.
The voltage drop across R S is . – . = . V.
This gives R S = .0V/( × – ) A = < . The nearest value of carbon resistor is < . So, a series resistor of < is appropriate. Note that slight variation in the value of the resistor does not matter, what is important is that the current I Z should be sufficiently larger than I L .
. . Optoelectronic junction devices We have seen so far, how a semiconductor diode behaves under applied electrical inputs. In this section, we learn about semiconductor diodes in which carriers are generated by photons (photo-excitation).
All these devices are called optoelectronic devices . We shall study the functioning of the following optoelectronic devices: (i) Photodiodes used for detecting optical signal (photodetectors). (ii) Light emitting diodes (LED) which convert electrical energy into light. (iii) Photovoltaic devices which convert optical radiation into electricity ( solar cells ).