| 摘要 |
1,189,274. Transistor time delayed switches. ALLMANNA SVENSKA ELEKTRISKA A.B. 2 June, 1968 [27 June, 1967], No. 30257/68. Heading H3T. A time delay circuit comprisesabridge having timing arms C, R and potentiometer arms P, a transistor controlling a relay L and having its emitter base path connected across the diagonal 6, 3 and a resistor R1 chosen such that the voltage drop across R1 when the transistor starts to conduct is equal to the voltage drop across the diagonal containing the emitter-base path. The resistor R1 allows the minimum time delay to be reduced below a value corresponding to the time to charge the capacitor to a value equal to the emitter-base threshold. As shown, the current producing the voltage across R1 is the charging current and this is supplemented at switching by positive feedback current from T2. When the circuit is switched off, the relay coil L is discharged through R1 and D and this provides feedback to speed the switching off. In Fig. 2 a diode D3 protects T1 against excessive reverse voltage and the voltage drop across R1 also compensates for the diode voltage drop. The relay is controlled by a thyristor Ty which provides feedback through D1 and C to the base of T1 to speed switching. In addition, the thyristor, when conducting, reduces the voltage at the upper terminal of potentiometer P to a value equal to the voltage across D4 so that there is no voltage across P and resetting is independent of the position of the slider. Diodes D4 also provide temperature compensation. |
