This document discusses different types of filter circuits used to reduce ripple voltage and increase average DC voltage output. It describes L-section filters which use an inductor to provide constant current to the load and reduce ripple voltage which is then filtered by a capacitor. Pi filters are also described where the capacitors provide a short circuit for AC and an open circuit for DC, while the inductor blocks AC and provides a short circuit for DC. The document also mentions using a bleed resistor to safely discharge capacitor charge over time when the load is removed.

1. Filter Circuits
Reduce ripple voltage therefore increase
average DC Voltage

2. Filtering with a Capacitor

3. LC or L Section Filter
L section filter connected to a full wave bridge rectifier
The inductor will operate as an inductor filter, attempting to keep
the current flowing through the load at a constant rate. The
reduced ripple voltage from the inductor will then be
filtered by the action of the capacitor as illustrated

4. Pi Filter
AC sees the capacitors as a short circuit and the inductor as a block
DC sees the capacitors as an open circuit and the inductor as a short
circuit
The AC of the will flow through C1 and be blocked by the inductor the
DC will not pass through the capacitor but will pass through the
inductor. Any AC not passed through C1 will then be “cleaned up” by
C2

5. Bleed Resistor
For safety a bleed resistor can be utilised to remove capacitor
charge over a pre determined time period.
Because the resistance of the bleed resistor is high (over 10 times the
load resistance) it does not effect load.
When the load is removed and the unit isolated the bleed resistor will
discharge the capacitors removing the stored charge.