What is the difference between fltering and regulating diode application?

Answer 1

Filtering: When you see the output of a bridge rectifier fed with ac, you will find that the output is actually a dc + ac. The ac can be filtered out reasonably using a filter. The filters used often are capacitive input filters, and in its simplest form has just one capacitor. the capacitor charges to the peak value of the ac, and discharges when the diodes do not conduct, due to a fixed load. The capacitor is usually selected as 1000uF per ampere of load if a ripple of about 6V pp can be tolerated. For a low voltage supply (such as 9V), this is far too high, and one may use 3000uF/ amp of load current and get 2Vpp ripple, at mains of 60 Hz. the ripple frequency is twice, at 120 Hz.

There is no regulating diode. One can have a regulator, and if it has large ripple rejection, one can use a lower value capacitor such as 1000uF for a 9V supply, and regulate the output to get a dc of 5V with low ripple of the order of 100mVpp or even lesser.