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.