Turning Off the Transistor

Chapter Turning Off the Transistor

Complete Electronics Self Teaching Guide with Projects
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Complete Electronics Self Teaching Guide with Projects

  • CHAPTER 4 THE TRANSISTOR SWITCH142ANSWERRB5V31 1kIn this calculation, VBE is included. 10  In practice, if the supply voltage is much larger than the 0.7-volt drop across the base-emitter junction, you can simplify your calculations by ignoring the 0.7-volt drop, and assume that all the supply voltage appears across the base resistor RB. (Most resistors are only accurate to within +/- 5 percent of their stated value anyway.) If the supply voltage is less than 10 volts, however, you shouldn’t ignore the 0.7-volt drop across the base-emitter junction.QUESTIONSCalculate RB for the following problems, ignoring the voltage drop across the base-emitter junction, if appropriate.A. A 10-volt lamp that draws 10 mA. β = 100. B. A 5-volt lamp that draws 100 mA. β = 50. ANSWERSA. ImAmAR voltsmABB5555V10100011001100kB. ImAmAR volts voltsmA voltsmABB55525510050250 72432215()kVVTURNING OFF THE TRANSISTOR 11  Up to now, you have concentrated on turning the transistor ON, thus making it act like a closed mechanical switch. Now you focus on turning it OFF, thus making it act like Book Author c04 V1 07/04/2012 2:59 PM c04.indd 1427/4/2012 3:00:35 PM