| 摘要 |
1397836 Transistor switching circuits PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 13 Oct 1972 [16 Oct 1971 12 April 1972] 47347/72 Heading H3T In a circuit arrangement including a transistor 6 having means 1 for applying a switching signal between the base and emitter and a load impedance 7 connected to the collector of the transistor, a diode 12 is provided between the base and emitter, the conductivity direction of the diode is opposite to that of the baseemitter junction of the transistor and at least one impedance 13 is arranged in series with the diode 12 and by which impedance the diode is brought to the conducting state after a minimum delay time of 1 ÁS. As shown the output transistor 6 is part of a sawtooth generator such as a horizontal deflection generator in a T.V. A squarewave signal from an oscillator feeds the transformer 1 and the negative voltage part of this signal brings the transistor 6 to the non- conducting state when the flyback period is initiated. A half oscillation follows during the flyback period in the deflection circuit 7 and the collector-base diode of the transistor 6 conducts so that the transistor operates in the inverse anode during the first half of the scan period. After a delay of at least 1 ÁS provided by inductors 13 such as ferrite beads the diode 12 conducts to limit the voltage at the base of the transistor 6 during inverse operation to obviate high dissipation produced in the base-emitter diode of the transistor 6. The delay may alternatively be provided by a saturable inductor (14, Fig. 2, not shown). In a further modification an additional transistor (17, Fig. 3, not shown) is connected in series with the diode 12 and is controlled by a suitable switching voltage from an additional winding on the output transformer so as to be non-conducting during the switching off of the transistor 6 and conductive during the inverse operation of the transistor 6. In this arrangement the diode 12 may be omitted and the base-emitter junction of the additional transistor 17 then provides the diode action and the collector-base diode forms the impedance. |
