TC 9-62
THE BASIC POWER SUPPLY
4-2.
Figure 4-1, view (A) shows the block diagram of a basic power supply. Most
power supplies are made up of the following four basic sections:
Transformer.
Rectifier.
Filter.
Regulator.
4-3.
Figure 4-1, view (B) shows the first section as the TRANSFORMER. The
transformer steps up or steps down the input line voltage and isolates the power supply
from the power line. The RECTIFIER section converts the AC input signal to a pulsating
DC voltage. However, you will see later on in this chapter that the pulsating DC is not
desirable. For this reason, a FILTER section is used to convert pulsating DC to a purer,
more desirable form of DC voltage. The REGULATOR section does just what the name
implies, it maintains the output of the power supply at a constant level in spite of large
changes in load current or input line voltages.
4-4.
Now that you know what each section does, let us trace an AC signal through the
power supply. At this point you need to see how this signal is altered within each section of
the power supply. You will see later how these changes take place. In Figure 4-1, view (B),
an input signal of 115 volts AC is applied to the primary of the transformer. The
transformer is a step-up transformer with a turns ratio of 1:3. You can calculate the output
for this transformer by multiplying the input voltage by the ratio of turns in the primary to
the ratio of turns in the secondary. Therefore, 115 volts AC x 3 = 345 volts AC (peak-to-
peak) at the output. Since each diode in the rectifier section conducts for 180 degrees of the
360-degree input, the output of the rectifier will be one-half, or approximately 173 volts of
pulsating DC. The filter section, a network of resistors, capacitors, or inductors; controls
the rise and fall time of the varying signal. Consequently, the signal remains at a more
constant DC level. You will see the filter process more clearly in the discussion of the
actual filter circuits. The output of the filter is a signal of 110 volts DC, with AC ripple
riding on the DC. The reason for the lower voltage (average voltage) will be explained
later in the chapter. The regulator maintains its output at a constant 110-volt DC level,
which is used by the electronic equipment (more commonly called the load).
Figure 4-1. Block Diagram of a Basic Power Supply
4-2
TC 9-62
23 June 2005
Previous Page
