Triac based Lamp Dimmer power control
This is a phase angle control of a Triac which is
a evolution from an SCR. The 50 Hz or 60 Hz
Sine wave of mains can be turned on at any point
after the Zero Crossing.
Edison
Bulb Life Extender
The Voltage ramps up in the sine wave which gives
a near "Linear" slope which can be used to
trigger the ON at a time delay after zero crossing
when the voltage is zero. This is like a PWM but
works on low frequency only. Some of the early
SMPS(HV for TV and Mains Inverter) by Siemens were
built around SCRs. Turning off a SCR is a
difficult job for a designer, MOSFETS and IGBT are
now used for PWM drive stages.
You can use it with a bulb to vary brightness of
bulb, this is a live circuit it can give a shock,
enclose in plastic box, the pot should have a
plastic knob, use a fuse, you can also use it for
temperature control of soldering irons.

The Source file is here del00004.zip
2N2646 based Voltage controlled SCR Pulser
A Center tap 50Hz Step Down Transformer with two
diodes is used to get a train of Positive Sine
Pulses at 100Hz which is applied to Q6 base via
R51. 2N2646
is a unijunction transistor(UJT) in a TO-18 metal
package. The control voltage or voltage proportional
to error is fed to R56-Q3,
Drive
or Fire Thyristors SCR with Pulses
The UJT drives a pulse transformer which provides
isolation from the Load which the SCR bridge is
controlling. This phase angle control gives a near
Linear closed loop control for a SCR bridge which
may be used in Electroplating or a Preregulator of a
big power supply.
Drive
SCR Thyristor with 555
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