tanx friend another one
how zener diodes work and i so some regulated circuit use these diodes what are the use of it
U can see the Reverse Bias (RB) i-v curve of zener diode:
The (reverse) voltage across the zener diode remains approximately constant over a wide current range (i.e. voltage constant for changing current). Keep in mind the voltage referred is usually the voltage across the device(here zener diode); it may be different than applied voltage & the current referred is the current through the device.
Regulation implies controlling certain parameter(s). There are 2 types of voltage regulation:
1)Line regulation: line means input voltage(Ein). Even if there is change in input voltage, say some fluctuation, o/p voltage (Vo=Vz) should remain constant.
2)Load regulation: load means the device to which o/p is delivered. Even if load, say a resistor(RL, shown in fig as a box), changes, the o/p should remain constant.
Now zener works as follows:
1)If Ei increases, since Vz is constant voltage across R(say Vr) increases & so, Vo=Vz=remains constant. Similarly for decrease in Ei, Vr decreases, Vo=Vz=constant.
2)If RL changes, say increases, since Vo=Vz=constant, less current flows through load as compared to previously. Assuming the current given by Ein source is constant, Iz changes & as previously stated, Vz remains constant for changes in Iz. Similar expln. for decrease in RL.
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why capacitors use in voltage regulator circuit what is the use of it
Cap Cin is necessary when regulator is not close to power supply filter circuit; the inductance of connecting wire (wire b/w filter & regulator) may produce oscillations. Bypass cap Cout used to improve the transient response of regulator and it ensures ac stability.
...IMHO you should refer to the capacitor suggestions in the datasheet...
Typical values for either bypass capacitor are from 0.1 to 1uF. the data sheet of 78xx series suggests 0.22uF for Cin and 0.1uF for Cout