| 摘要 |
1,257,531. Control of A.C. motors; control systems for consumption apparatus. GENERAL ELECTRIC CO. 13 March, 1969 [15 March, 1968], No. 13405/69. Headings H2H and H2J. [Also in Division G3] A triac 48, which is connected in series with load 42, is fired by the discharge of capacitor C1, a bridge rectifier D1-D4 having its fullwave voltage clamped by Zener diode D9 and transistor Q13 to supply a ramp-and-pedestal voltage generator and a reference voltage generator from terminals 1, 10. Adjustment of a voltage divider RA, RB, controls the firing angle of the triac in each half-cycle of the A.C. supply. The ramp-and-pedestal generator comprises a timing capacitor C2 which is charged rapidly to a pedestal voltage level from the voltage divider RA, RB. Thereafter, in the same half-cycle, the capacitor C2 is further charged by half sine-wave current through transistor Q10 and resistor Ra. The ramp-and-pedestal voltage at terminal 13 is compared with a reference voltage at terminal 2. Transistors Q3, Q4, function as a differential amplifier, whilst transistors Q4, Q5, present a high impedance to the timing capacitor and compensate for the base-emitter drop of the transistor Q12. When load current flows through the triac 48, transistors Q7, Q8, Q9, are non-conductive to prevent the comparator from delivering a triggering signal, the value of resistor R1 determining the voltage across the triac required to enable the comparator. During operation of the comparator, the transistor Q3 conducts when the ramp voltage becomes equal to the reference potential, thereby keying the switches Ql, Q2 and causing the triac 48 to conduct. The capacitor C2 is reset to a fixed level at the end of each half-cycle by means of transistor Q6. The circuit elements within the line 51 may be embodied in a monolithic integrated semiconductor body including a substrate which is separated from the remaining portions of the integrated circuit by PN junction diodes which are prevented from becoming forward biased; Figs. 5, 6 (not shown). For this purpose, diodes D3, D4, are replaced by an isolation circuit comprising two pairs of transistors, whilst the switches Q1, Q2, are replaced by a bilateral switch. An additional transistor compensates for the low gain of transistor Q12, and diodes D1, D2, are replaced by four base-emitter diodes. The load 42 may be resistive, or consist of a single-phase induction motor with a phase-splitting capacitor. A tachometer generator may be coupled to the motor to provide a control signal across terminals 10, 12, the output of the generator being filtered and applied to a speed-setting potentiometer, Fig. 7 (not shown). The triac 48 may be replaced by a pair of inverse thyristors, each having a pulse transformer, Fig. 8 (not shown). |
