why are Voltage Regulators in between load and filters? And what is the purpose of filters?

 

Because that is how they are used. It's like asking "Why does the sock go between the foot and shoe?"

You have to be more specific. Can you show a schematic?

 

why are Voltage Regulators in between load and filters? And what is the purpose of filters?

To regulate the DC. Filter smooths the pulsating DC so the regulator can work properly.

 

A linear voltage regulator is not supposed to pulsate. It is a linear feedback control system. The capacitor on the output pin is to slowdown the response time of the feedback circuit and prevent it from going into high frequency oscillation.

 

A linear voltage regulator is not supposed to pulsate. It is a linear feedback control system. The capacitor on the output pin is to slowdown the response time of the feedback circuit and prevent it from going into high frequency oscillation.

From what I read , the cap on the output is necessary if the output is more than 6 inches from the regulator and my guess is that the capacitance of the wires comes into play at that distance . Am I right?

 

No. On every 3-terminal voltage regulator you need about 1μF at the output pin to GND to prevent oscillation.

At your load you can add 10μF to 100μF to smooth out load fluctuations.

 

From what I read , the cap on the output is necessary if the output is more than 6 inches from the regulator and my guess is that the capacitance of the wires comes into play at that distance . Am I right?

Almost.. Its the input though not output. 6" or more away from the input filter an input bypass cap should be used.

 

You also need a minimum cap at the output to prevent oscillation as MrChips said. The minimum value is listed in the datasheet.

 

From what I read , the cap on the output is necessary if the output is more than 6 inches from the regulator and my guess is that the capacitance of the wires comes into play at that distance . Am I right?

It's actually the inductance of the wires decoupling the effect of the output cap, but you have the basic idea right. Most linear regs need at least about 1uF of cap within about one cm of the output terminal. Large caps out near the load are to provide peak currents to the loads.

 

The OP asked about the the regulator being between the load and filter so he was referring to the input capacitor not the output capacitor. The purpose of that capacitor is to smooth any pulsations from the raw DC source (as wmodavis in post #3 noted). From that point the thread got sidetracked into discussing the output capacitor.