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Electronics Schematics - U

Unijunction Transistor Circuits

Acceptable Voltage Indicator - I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is high, low or OK.  When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level.....(designed by David A. Johnson, P.E.)

Low Battery Voltage Flasher - This circuit is designed to monitor two alkaline cells (3v) that from the battery often used in portable electronic equipment. It use an inexpensive IC from Panasonic that is connected to an efficient LED flashing circuit. When the battery voltage drops below a certain point the circuit flashes the LED. In the off state the circuit draws only 1uA, while in the active flashing state it draws 20uA. Published in EDN, Jan 2, 1997...(designed by Dave Johnson)

Poor Man's Frequency Converter for a squirrel Motor - The idea is opposite of typical motor frequency converter 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

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.

UJT Test - This testing procedure is for use with a digital multimeter in the OHM's test-range.  The UJT is a solid-state 3-terminal (TO-18 case) semiconductor.  UJT's are used in pulse/timing, oscillator, sensing, and thyristor triggering circuits. The most common one being probably the 2N2646 from Motorola. Tony van Roon's design

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 ... (app note)


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