Unregulated Linear Power Supplies

Different rectifier circuits can be used when building unregulated linear power supplies.
The most common circuits are shown below.

1. Dual Complementary Rectifier

A dual complementary rectifier is the best choice, when a positive and negative
DC output of the same voltage is required. The secondary windings are bifilar wound
for precisely matched resistance, coupling and capacitance.

2. Full Wave Bridge

The full wave bridge rectifier is the most cost effective, since the entire
transformer secondary is used on each half cycle and no center tap is required.

3. Full Wave Center Tapped Circuits

A full wave center tapped rectifier is commonly used in high current, low voltage applications, since there is only one voltage drop in the
 circuit. However, since only one secondary winding is used at a time, the power rating of the transformer has to be about 30% greater than
 for a full wave bridge transformer.

4. Full Wave Center Tap With Choke Input

Choke input filters are commonly used in high current applications, since they reduce
ripple and allow better utilization of the power  capacity of the transformer.

Regulated Linear Power Supplies

 Regulated linear power supplies are used to provide a constant output
voltage for different loads and varying input voltage.

HOW TO SPECIFY THE TRANSFORMER
 A simplified formula to determine the AC voltage and current of the transformer is as follows:

Vdc = Output DC voltage
Vreg = Voltage drop in the regulator = 3 Volt
Vrec = Voltage drop in the diodes = 0.7 Volt
Vrip = Ripple voltage = 10% of Vdc
Vnom = Nominal input voltage = 117 Volt
Vlow = Low line input voltage = 98 Volt
0.9 = Rectifier efficiency

The transformer AC voltage and current, when used in the various
rectifier circuits, is calculated as shown below:

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