Power Supply Filter Capacitor Design

The bigger the capacitor the lower the resulting ripple voltage.

Power supply filter capacitor design. Correct design of the decoupling filter ensures that it won t cause more problems than it solves. The lc filter shown in fig. Because these capacitors have a dc value they are actually storing a lot of energy that never gets used. This is the most basic form of power supply design which uses a single diode and a capacitor.

In addition to the natural output capacitance of the power supply you might add a series inductor and another filter capacitor to further reduce output noise fig. Either lc or rc low pass filters can be used to remove the ripple remaining after the reservoir capacitor. L c filters power supply filters. The inductor passes dc.

1 2 4 but for basic power supplies lc designs are less popular than rc as the inductors needed for the filter to work efficiently at 50 to 120hz need to be large and expensive. The filter capacitor must usually be large to provide an acceptable level of filtering. Since a single diode will rectify only one half cycle of the ac signal this type of configuration requires a large output filter capacitor for compensating the above limitation. Putting it to work a practical example.

This large current may damage the diode and at the same time it causes greater heating of the power transformer resulting in decreased efficiency. Assume that we want to make a 9v 500ma power supply using the lm7809 voltage regulator device 12v transformer bridge rectifier and filter capacitor. Depending on the power supply the smoothing capacitor is combined with other circuits. For example a 10 ripple in a 5 v power supply means that the actual output voltage varies by 0 5 v.

Regardless of the frequency with which the input voltage is applied a capacitor is used in order to reduce the remaining resistance after rectification. A simple power supply decoupling filter made from an inductor and capacitor covers the gap between about 10khz and 1mhz. The chart above shows typical power supply filtering frequency ranges. For a typical 5 v power supply a 2 200 μf electrolytic capacitor will do the job.

Simple shunt capacitor filter reduces the ripple voltage but increases the current through the diode. 1 2 3 is more efficient and gives better results than the rc filter shown in fig.