新型电子第3章资料.pptVIP

Words： 1. diac 双向触发二极管 2. bidirectional 双向的 3. phase shift 移相 4. triac 三端双向触发晶闸管 5. pronounced 显著的 6. silicon bilateral switch （SBS） 硅双向开关 7. Transistor Switch 晶体管开关 8. saturation 饱和 9. induction coil 感应线圈 10. ignition coil 点火线圈 11. optoisolator 光绝缘体 CHAPTER 3 THE DIAC AND SILICON BILATERAL SWITCH 3.1 the diac （双向触发二极管） The diac is a special-purpose bidirectional diode. Its primary fuction is to phase shift a triac. 1. schematic symbols of diac 2. characteristics (1) a bidirectional device (2) operating in an AC circuit comparing with UJT and PUT, the operation condition 3. working principles (negative resistance) characteristic voltage curve of diac a. when the voltage applied to the Diac is below the predetermined voltage (15V), it remains in turned-off state b. when the voltage applied to the Diac is beyond the predetermined voltage (15V), it turns on c. When the diac fires, it displays a negative resistance. Meaning that it conducts at a lower voltage than that which was applied to it (assume voltage 5V) d. The diac remains turned on until the applied voltage drops below its conduction level, or 5 volts. 4. Analysis of the diac (1) the circuit since the diac is a bidirectional device, it conducts on either half cycle of the AC voltage applied to it. The simplest way to sum up the operation of the diac is to say it is a voltage-sensitive AC switch. (2) working process Ⅰ. During the positive half cycle of US a. when US is below 15volts 1) the Diac is in off state 2) I=0, UR=0, UD= US b. when US is above 15volts (a) the Diac turns on