1. 1 13. Pulsed waveforms and Timing Circuit Design 13.1Op. Amp. Pulse GeneratorsOp. Amp. Pulse Generators 13.2555 timer IC Oscillator555 timer IC Oscillator 13.3555 Timer Variable Duty Cycle Circuits555 Timer Variable Duty Cycle Circuits 13.4555 Timer Monostable Circuits555 Timer Monostable Circuits

2. EE3601-13 Electronics Circuit Design 2 13.1Op. Amp. Pulse Generators Study example 14.7-page786 for this pulse generator with diode

3. EE3601-13 Electronics Circuit Design 3 Summary of Design Equations Op. Amp. Pulse Generators

4. EE3601-13 Electronics Circuit Design 4 Example: Given the Op. Amp. Pulse Generator circuit below, (a) calculate and sketch the output waveform (b) frequency output and (c) duty cycle of the output waveform if C = 0.1  F, R = 20k , R 1 = R 2 = R 3 = 1k  Example: Given the Op. Amp. Pulse Generator circuit below, (a) calculate and sketch the output waveform (b) frequency output and (c) duty cycle of the output waveform if C = 0.1  F, R = 20k , R 1 = R 2 = R 3 = 1k 

5. EE3601-13 Electronics Circuit Design 5 Example: Design the Op. Amp. Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of 20%. (a) Sketch the output waveform (b) Design all charging and discharging resistors if C = 0.1  F and voltage divider resistors R 1 = R 2 = 1k  to provide threshold voltage to the generator. Example: Design the Op. Amp. Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of 20%. (a) Sketch the output waveform (b) Design all charging and discharging resistors if C = 0.1  F and voltage divider resistors R 1 = R 2 = 1k  to provide threshold voltage to the generator.

6. EE3601-13 Electronics Circuit Design 6 13.2555 timer IC Oscillator RS-Flip-flop Reset(R) or Set(S) with logic high input Comparators More positive applied to the positive terminal (or more negative applied to the negative terminal will make output high If pin 4 (Reset pin) is less than V CC, PNP BJT conducts and (R) becomes high to reset the Flip-flop Output is zero if Reset and high (V CC ) if Set Discharge pin 7 is zero if Reset and floats if Set 555 Timer

7. EE3601-13 Electronics Circuit Design 7 1. If Threshold pin 6 is more than 2/3 of V CC, “ R ” will be high and output Q is Set to zero 2. If Threshold pin 6 is less than 2/3 of V CC, there is no change at output Q 3. If Trigger pin 2 is less than 1/3 of V CC, “ S ” will be high and output Q is Set to V CC 4. If Trigger pin 2 is more than 1/3 of V CC, there is no change at output Q 5. If Modulate pin 5 is connected to a dc source or to external resistor, pin 2 and pin 6 levels will be no longer 1/3 or 2/3 of V CC but will be changed to any other levels.

8. EE3601-13 Electronics Circuit Design 8 Astable Multivibrator (pulse generator) #2. But V C is never charged to V CC because when V C =just above (2/3)V CC pin 6 takes care and the output pin 3 will reset. #3. When pin 3 is reset(=low). Pin 7 will be zero. Then C is discharged to 0 through R 2 =R d #4. But V C is never discharged to 0 because when V C = just below (1/3)V CC pin 2 takes care and the output pin 3 will set. It repeats step #1 again. #1. Let pin 3 is set (=high). Pin 7 will float. Then C is charged to V CC through R 1 +R 2 =R C

9. EE3601-13 Electronics Circuit Design 9 Pulse frequency and duty cycle

10. EE3601-13 Electronics Circuit Design 10 Continuous and step Pulse frequency Discharge R 2 is varied to get continuous change of discharge time t d which will vary both frequency and duty cycle Decade step of capacitor C 1 =10C 2, C 2 =10C 3 is switched to get step change of “ T ” which will vary the frequency but duty cycle remains the same R 1 is varied to change charge R 1 + R 2 to get continuous change of charge time t c which will vary both frequency and duty cycle

11. EE3601-13 Electronics Circuit Design 11 13.3555 Timer IC Variable Duty Cycles Circuits By using a diode to bypass R 2 while charging the capacitor, the t c is found from R 1 alone and t d is found from R 2 alone. If R 2 = R 1 then duty cycle = 50% If R 2 > R 1 then duty cycle > 50% If R 2 < R 1 then duty cycle < 50% Now t c = CR 1 ln2 and t d = CR 2 ln2 Duty=(CR 1 ln2)/(CR 1 ln2 + CR 2 ln2 ) = R 1 /(R 1 +R 2 )

12. EE3601-13 Electronics Circuit Design 12 13.4555 timer IC Monostable Circuit Monostable Multivibrator (timer) #3. Now C is charged to V CC through R. Output pin 3 is then high #4. But V C is never charged to V CC because when V C = just above (2/3)V CC pin 6 takes care and the output pin 3 will reset. And it stays stable at reset all the time until another external trigger. #1. Let pin 2 is high and pin 3 is low. Pin 7 will zero. Output is also zero. Then C is also discharged to 0 through pin 7 #2. When pin 2 is triggered to zero for a short time, Pin 3 will be high. Then pin 7 is floating.

13. EE3601-13 Electronics Circuit Design 13 Summary of Design Equations 555 Oscillator and Timer Astable Multivibrator 1 Astable Multivibrator 2 Astable Multivibrator 3 Monostable Multivibrator

14. EE3601-13 Electronics Circuit Design 14 Example: Design the 555 Timer IC Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of 80%. (a) Sketch the output waveform (b) Design all charging and discharging resistors if C = 0.1  F (c) Sketch the circuit. Example: Design the 555 Timer IC Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of 80%. (a) Sketch the output waveform (b) Design all charging and discharging resistors if C = 0.1  F (c) Sketch the circuit.

15. EE3601-13 Electronics Circuit Design 15 Example: Design the 555 Timer IC Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of (a) 50%. (b) 20% (c) 80% Design all charging and discharging resistors if C = 0.1  F (c) Sketch the circuit. Example: Design the 555 Timer IC Pulse Generator circuit to generate a 500Hz waveform at a duty cycle of (a) 50%. (b) 20% (c) 80% Design all charging and discharging resistors if C = 0.1  F (c) Sketch the circuit.

16. EE3601-13 Electronics Circuit Design 16 Example: Design the 555 Timer IC Pulse Generator circuit to generate a 20Hz to 250Hz waveform by using a minimum discharge resistance of 1k . (a) Sketch the output waveform (b) Design all charging and discharging resistors if C 1 = 0.1  F (c) Sketch the circuit (d) what is the maximum frequency of this generator if a decade step uses 2 more capacitors C 2 =0.01  F, C 3 =0.001  F?

17. EE3601-13 Electronics Circuit Design 17 Example: Design the 555 Timer IC circuit to generate a 100ms pulse. (a) Design C if charging resistors is 1M  (b) Sketch the circuit. Example: Design the 555 Timer IC circuit to generate a 100ms pulse. (a) Design C if charging resistors is 1M  (b) Sketch the circuit.