| 摘要 |
<p>1,090,859. Transistor delayed switching circuit. PHILIPS' GLOEILAMPENFABRIEKEN N.V. Nov. 2, 1964 [Nov. 5, 1963], No. 44548/64. Heading H3T. [Also in Divisions G3 and G4] A cooking time alarm circuit for egg-boiling includes a temperature-sensitive resistor 5 for immersion in the water and an alarm buzzer 29 in circuit with a switch 20 controlled by a relay 17. When resistor 5 is cold, transistor 1 is conducting. A diode 20 and transistor 3 are also conducting and a Miller condenser 12 is charged. The current through transistor 2 is negligible. Transistor 4 is conducting so that the relay 17 holds switch 60 off. When the water has reached, say, 70‹ C., transistor 3 is cut off. Transistor 2 begins to conduct and condenser 12 is discharged at a very low rate. As boiling point approaches the voltage drop across resistor 10 decreases and condenser 12 discharges more rapidly. This time is adjustable by resistor 11. Eventually, transistor 4 is cut off, switch 60 returns to rest position and the alarm buzzer 29 is operated. In a modification, Fig. 2 (not shown), the circuit includes an emitter follower in the Miller feedback circuit and a voltage stabilizing network supplying D.C. from an A.C. mains.</p> |
