Linear supply uses switch-mode regulation


Posted on Feb 2, 2013

In Figure 1 , a basic and versatile 5V supply uses a zener diode and an emitter-follower transistor. You must calculate and design the transformer such that Q1 is close to saturation at low mains voltages and nominal output current. Additionally, you must choose R1 to ensure proper bias for the zener diode.



A TO-92 small-signal transistor, such as a BC337, is adequate for 300 mA, but a medium-power device, such as a BD135, is a better choice. To cut costs, this design uses no heat sink. Inasmuch as the circuitry is inside a nonventilated plug-in plastic case




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