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Unijunction Transistor Circuits
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Poor man's Frequency Convertor for a squirrel Motor: The
idea is opposite of typical motor frequency convertor where the
main voltage is first rectified and later chopped to a variable
frequency. Outputting voltage must be in proportion of
frequency. The lower the frequency the lower the voltage must
be. This simple circuit is operating as a cycloconverter. It
picks every 3th half wave of the inputting main voltage. The
result is 1/3th from the frequency and even from the voltage.
It is near ideal and comparable to the normal motor frequency
convertor. Only limitation is the speed control. This is not
stepless but usable speeds are 1/3th, 1/5th, 1/7th and so on
from the mains freq. This circuit is dimensioned to the 1/3
frequency division. Increasing time constant of R2C1 it can
operate in more lower speeds. |
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Relaxation Oscillators: A relaxation oscillator is a
circuit that repeatedly alternates between two states at with a
period that depends on the charging of a capacitor. The
capacitor voltage may change exponentially when charged or
discharged through a resistor from a constant voltage, or
linearly when charged or discharged through a constant current
source. With exponential charging, the timing is expressed in
terms of time constants RC. In a basic circuit |
Silicon Controlled Rectifier Model Railroad Throttles and London
Model Railroad Group SCR Throttle: The following is a
schematic drawing of a Silicon Controlled Rectifier type
throttle for use on larger scale model railroads. Three versions
of this throttle are shown on this page. They are not
sophisticated designs but work well and are tough and reliable.
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Unijunction Transistor: The unijunction transistor(UJT) is
a three terminal device with characteristics very different from
the conventional 2 junction, bipolar transistor. It is a pulse
generator with the trigger or control signal applied at the
emitter . This trigger voltage is a fraction (n) of interbase
voltage, Vbb.The UJT circuit symbol, junction schematic, and
characteristic curve are |
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