capacitor use problems

[Nipuna56]

this is the image

 

[jeffrey samuel]

in case parallel connections the effective capacitance gets added up and so there are about 101 ufarads connected to the ckt

but the purpose of the first is to feed the ip AC to the LM regulator and the second 101 uF is for filtering the op

 

[FvM]

the purpose of the first is to feed the ip AC to the LM regulator and the second 101 uF is for filtering the op

The values don't make much sense, however. If the input to the circuit is AC, then a reasonable filter capacitor value for 1 A output current would be several 1000 µF. Output filtering with 100 µF is very unusual, it may be possibly required for pulsating loads.

IMHO you should refer to the capacitor suggestions in the datasheet. If the input is AC with rectifier, the capacitor value has to be caculated according to input voltage and output current.

 

[jeffrey samuel]

So the design has some errors in it sir FvM

 

[FvM]

So the design has some errors in it sir FvM.

They look like been arbitrary choosen. They may be still reasonable under special conditions, but not as a general suggestion.

 

[jeffrey samuel]

There is a problem here which i never saw the first cap of 100 uF is a filter after rectification and the second is for increasing the time constant

about the other two cap they just lead the dc supply away from the load to the op but using them in parallel config really took me there

i suggest you to use a Zener diode instead of the second cap in front off the 7805 thing so that the op will have very few ripples in it

 

[Nipuna56]

what about 2 caps after 7805 what are their duties

 

[etmabreu]

Depending on the load, 100uF may be enough.

Usually one does not put large capacitors after a 78xx, since it will degrade the regulator's response (one is placing a large pole at the output of a feedback circuit).

 

[jeffrey samuel]

Better reduce it to 10 uF and that is enough here

 

[Marvel_tronix]

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