Linear Power Supplies

Unregulated Linear Power Supplies

When building unregulated linear power supplies, different rectifier circuits can be used. The most common circuits are the following:

Dual Complementary Rectifier

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

Full-Wave Bridge

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

Full-Wave, Center-Tapped Circuits

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

Full-Wave Center-Tap with Choke Input

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

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

The formula to determine the transformer’s AC voltage and current (simplified version):

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

Calculations for the transformer’s AC voltage and current, when used in the various rectifier circuits:

Rectifier circuitsRMS voltages (V)RMS current (A)
Dual complementaryVAC = 1.03VDC + 3.47IAC = 1.8 X IDC
Full-wave bridgeVAC = 1.03VDC + 4.13IAC = 1.8 X IDC
Full-wave center-tappedVAC = 1.03VDC + 3.47IAC = 1.3 X IDC