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Unijunction Transistor Circuits

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.
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.
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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