A.c. control devices

Claim 1

An alternating-current control device including a semiconductor switch element (Tr) having a plurality of terminals including a pair of load terminals connected in series relationship with a load across a pair of A.C. power supply terminals and a gate control terminal connected to one terminal of a bilateral switching diode (D1) for receiving firing pulses issued therefrom, said diode (D1) having a second terminal connected to a firing circuit arrangement, more particularly to the junction between a resistor (R1) and a first capacitor (C1) connected in series therewith, which series-circuit Is parallelconnected to said semi-conductor switch element, said control device further including a compensation capacitor (C2) connected in series to a pair of parallel-connected circuits and included in a circuit connected in parallel to said first capacitor (C1), said last-mentioned circuit serving to affect the rate at which said first capacitor (C1) is charged, said parallel-connected circuits being of opposite polarity and each including a series circuit of a diode (D2) and (D3), respectively, and first transistors (T1) and (T2), respectively, characterized in that one of said transistors (T2) is included in a grounded emitter circuit configuration, the other of said first transistors (T1) being included in a grounded collector circuit configuration and being controlled by a third transistor (T3) included in a grounded base circuit configuration, the base of said one first transistor (T2) and the emitter of said third transistor (T3) being connected through a resistor to one of a pair of D.C. control voltage input terminals, and that both said first transistors (T2) and (T1) are respectively provided with base emitter resistors (R4), (R2), base collector resistors (R5), (R3), and base collector capacitors (C4), (C3), the arrangement being so dimensioned that the voltage developed across said first capacitor (C1) increases gradually over a range corresponding with a virtually complete half-excursion of the A.C. power voltage applied to said pair of A.C. power supply terminals, the amplitude of said voltage being determined by the magnitude of D.C. control voltage applied across said D.C. control voltage input terminals.