tailieunhanh - (McGraw-Hill) (Instructors Manual) Electric Machinery Fundamentals 4th Edition Episode 1 Part 5

Tham khảo tài liệu '(mcgraw-hill) (instructors manual) electric machinery fundamentals 4th edition episode 1 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3-8. Note The above discussion assumes that transformer T3 is never in either state long enough for it to saturate. Figure P3-3 shows a relaxation oscillator with the following parameters R1 variable R2 1500 Q C ụF Vdc 100 V VBO 30 V IH mA a Sketch the voltages vC t vD t and vo t for this circuit. b If R1 is currently set to 500 kQ calculate the period of this relaxation oscillator. Solution a The voltages vC t vD t and vo t are shown below. Note that vC t and vD t look the same during the rising portion of the cycle. After the PNPN Diode triggers the voltage across the capacitor decays with RR time constant T2 0 0 C 2 R1 R2 while the voltage across the diode drops immediately. 75 b When voltage is first applied to the circuit the capacitor C charges with a time constant T1 R1 C 500 kQ pF s. The equation for the voltage on the capacitor as a function of time during the charging portion of the cycle is vC t A B e Rc where A and B are constants depending upon the initial conditions in the circuit. Since vC 0 0 V and vC - 100 V it is possible to solve for A and B. A vC - 100 V A B vC 0 0 V B -100 V Therefore vC t 100 -100 e V The time at which the capacitor will reach breakover voltage is found by setting vC t VBO and solving for time t1 76 n _100 V - 30 V t In- 7--- 178 ms 1 100 V Once the PNPN Diode fires the capacitor discharges through the parallel combination of R1 and R2 so the time constant for the discharge is T 500ff AF s The equation for the voltage on the capacitor during the discharge portion of the cycle is VC t A B e T VC t Vbo e T The current through the PNPN diode is given by Id t Vr e R2 If we ignore the continuing trickle of current from R1 the time at which iD t reaches IH is t -R C ln hb - ln A 1500 a ms 22 VBO 30 V Therefore the period of the relaxation oscillator is T 178 ms ms ms and the frequency of the relaxation oscillator is f 1 T Hz. 3-9. In the circuit in Figure