| 摘要 |
A variator circuit comprises a triac (4) mounted in series with a load (1) to be controlled, and a CTR variable series phase-shifter circuit (8, 9, 10). The point (11) midway between the resistive element (8, 9) and the capacitive element (10) of said circuit (8, 9, 10) is connected to the gate (6) of the triac. Connected in series in the branch of the circuit comprising the resistive element and the connection of said midway point to the triac is a non-linear component (18) the resistance of which can change from a minimum value to a maximum value when the current flowing through it increases by a minimum value corresponding to the normal operating conditions of the phase-shifter circuit to a maximum value corresponding to a short-circuit condition of the triac between the gate and the power electrode, said minimum value of the resistance being a value which has no appreciable effect on the functioning of the phase-shifter circuit and said maximum value of the resistance being a value which limits the current in the resistive element to a value which prevents any destruction or deterioration of the latter. Said non-linear component may be a CTR resistor, a fast safety fuse or, very advantageously, the filament of an incandescent lamp, the characteristics of said filament, in particular its equivalent resistance under nominal operating conditions, being chosen so that it volatilizes in the event of a short-circuit condition of the triac between the gate and the power electrode.
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