In this project a relatively efficient pre-regulator is added at  the input of a DC series-pass regulated power supply. This minimizes the power losses by reducing the dissipation especially at low output voltages and high currents. Instead of using Optically Isolated TRIAC drivers with pulse control  this design presents a novel analog optical-feedback loop to realize a pre-regulator using a combination of a Light-Emitting-Diode (LED) and Light-Dependent-Resistor (LDR). With this technique the 24V 1A variable DC power supply linear regulator dissipation is restricted to less than 7W.



The design data includes PCB's, circuit diagrams and Calculations.

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This 24V variable power supply project presents a novel application of an optical feedback loop using a LED and LDR to control a TRIAC within a standard Fan Regulator. This implements  a pre-regulator for the Linear Output Stage. The maximum linear regulator dissipation is less than 7W demonstrating effective operation of the pre-regulator. The SMPS and overall efficiencies are also plotted for completeness.