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12-6 Zener Diode Regulator:

The zener diode works on the principle of reverse current breakdown - and the breakdown voltage or zener voltage ranges between 2 to 200 volts in all its types - when the reverse voltage applied to it increases to the value specified for each zener, the diode collapses, and at this point the reverse current increases rapidly and then the characteristic appears Useful for the Zener diode - in the region of operation of the diode, its voltage is almost constant within a wide range of the Zener current, and this is the special voltage of the diode. And thus maintains the stability of the feeding voltage with a value equal to the Zener voltage.

Zener current:

The maximum zener current is determined by the power allowed to dissipate in it, and the maximum zener current ranges between several milliamps and tens of amperes.

The zener diode whose breakdown voltage is less than (1 volt) has a negative thermal factor. That is, the breakdown voltage decreases with increasing temperature - as for Zener diodes that have a breakdown voltage higher than

(6 volts), so the thermal factor is positive. That is, the breakdown voltage increases with increasing temperature.

Zener diode regulation circuit:

Diagram 10-12 shows the voltage regulation circuit using a Zener diode (CR) - the input voltage (11) volts DC is irregular - while the output voltage is regulated DC (which is a Zener voltage. That is, the voltage is constant even if the input voltage changes between (9) 5.5 - 14 volts) - with a current for the load less than (4.5 milliamps), and if the input voltage is greater than 9.5 volts, as shown in the figure, the zener will break down, and only (75) volts will appear on both ends, and the difference between the two voltages is 3.57-11. .5 volts will appear through the series resistance: its current is 305 milliamps = 7 milliamperes, and this current is divided between the load (22 k ohm), and the zener diode - the load current is equal to 2005 i.e. (3.41 milliamps), and the zener current is (-7 3.41 - 3.59 mA). Input voltage changes: When the input voltage increases, more current will pass through the diode and more voltage will be lost in R and the voltage will remain constant. If the input voltage decreases, the current passing through the diode will decrease, and the lost voltage will decrease at R and the output voltage remains 7.5 volts.

Load current changes:

When the load current increases while the input voltage remains constant, the voltage increases - and this leads to a decrease in the zener current, and its voltage remains constant. When the load current decreases, the opposite happens - that is, the lost voltage across the resistance R decreases, and thus the zener current increases, and the voltage at the output remains constant at 7.5 volts. In conclusion, if the input voltage changes or the load changes, it will be compensated by a change in the diode current - or a change in the voltage at both ends of the series resistance. with the circuit. Thus, the zener voltage remains constant