Condition responsive motor control having unijunction firing circuit for a triggeredswitch

摘要

1,169,015. Control of A.C. motors. A. O. SMITH CORP. 21 Oct., 1966 [22 Oct., 1965], No. 47345/66. Heading H2J. [Also in Division G3] An A.C. motor is energized via a triggered switch (semi-conductor device 8) which conducts in either direction when triggered at 11, the triggering circuit comprising a unijunction transistor 14 in series with a pulse transformer 13 across a rectifying bridge 26-29, the phase angle of the triggering pulse being dependent on the time constant of a capacitor 36 circuit which includes a condition responsive device, e.g. a thermistor 18. The thermistor detects the temperature of a refrigerator condenser 2 and the system controls the speed of a split phase induction motor 7 driving a cooling fan 6. The unijunction transistor is made insensitive to ambient temperature by a potential divider 32, 33. Resistor 24 and capacitor 25 absorb the back e.m.f. The circuit elements may be mounted as integral with the end frame of the motor.