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Line Power Supply
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This circuit provided a regulated output without a power transformer.  It is similar to common circuits, except that a zener diode is replaced with an SCR.  This is far more robust against line voltages surges than a zener diode version, plus there is no heat generation.  C1 sets the available current (20mA/uF @ 60Hz).  R2 sets the output voltage (-.55V/K).  The bipolar outputs are separately adjustable by R3 and R5.

In the bipolar version, you could replace SCR1 with a small TRIAC and delete SCR2.  L1 can be deleted, but it prevents possible interference with X-10 units.  R1 acts as a fuse and an inrush current limiter.  The high side of R3 can be moved to the other side of D2 for slightly better regulation, but slower transient protection and a little more energy loss.  This circuit is ideal for applications where a relay of heavy load is switched on and off, that would cause overheating of a zener diode regulator.

More:  Ac to DC Power SuppliesRegulated Power Supplies Voltage Regulator Circuits
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