Questions

1. Determine the time \(T\) for the \(\text{ON}\) state of the monostable multivibrator using \(\text{IC } 555\) having \(\text{R} = 1.2 \,\text{k}\Omega\) and \(\text{C} = 0.1 \,\mu \text{F}\).
2. Determine the frequency of the astable multivibrator circuit using \(\text{IC } 555\) with \(\text{R}_{\text{A}} = 3 \,\text{k}\Omega\), \(\text{R}_{\text{B}} = 2.7 \,\text{k}\Omega\) and \(C = 0.033 \,\mu\text{F}\).
3. Design an astable multivibrator using \(\text{IC } 555\) to generate a square wave of frequency \(1 \,\text{kHz}\) with a duty cycle of \(60 \,\%\) by choosing suitable resistor and capacitor values.
4. Calculate the output pulse width of a monostable multivibrator using \(\text{IC } 555\) which is triggered by a negative pulse. If \(\text{R} = 100\,\text{k}\Omega\) and \(\text{C} = 10 \,\mu \text{F}\).
5. What is the final output frequency of An astable multivibrator using \(\text{IC } 555\) which generates a \(2 \,\text{kHz}\) square wave and this output is fed to a \(\text{T flip-flop}\) to divide the frequency.
6. Design a circuit to generate a \(50 \,\%\) duty cycle square wave at \(10 \,\text{kHz}\) using \(\text{IC } 555\).
7. Calculate the change in duty cycle for an astable multivibrator using \(\text{IC } 555\) operating at \(5 \,\text{V}\) supply when the control voltage varies from \(2 \,\text{V}\) to \(4 \,\text{V}\) to generate a PWM signal for a motor speed control.
8. A monostable multivibrator using \(\text{IC } 555\) is required to generate a precise \(10 \,\text{ms}\) pulse. Calculate the tolerance if \(\text{R} = 10 \, \text{k}\Omega\), \(\text{C} = 1 \, \mu F\), with \(\pm 5 \,\%\) tolerance each.

Answers

1. \(T = 1.1 \,\text{RC} = 132 \,\mu\text{s}\)
2. \(f = \frac{1.44}{(\text{R}_{\text{A}} + 2\text{R}_{\text{B}})\text{C}} = 5.19 \,\text{kHz}\)
3. \(\text{R}_{\text{A}} + 2\text{R}_{\text{B}} = \frac{1.44}{\text{fC}} = 144 \, \text{k}\Omega\); \(\quad\text{Assumed: } \text{C} = 0.01 \, \mu \text{F}\); \(\text{R}_{\text{A}} + R_{\text{B}} = 86.4 \,\text{k}\Omega\); \(R_{\text{A}} = 28.8\,\text{k}\Omega\), \(R_{\text{B}} = 57.6\,\text{k}\Omega\)
4. \(T = 1.1\,\text{RC} = 1.1 \, \text{s}\)
5. \(\text{IC } 555\) astable output \(= 2 \,\text{kHz}\), \(T\) flip-flop divides frequency by 2 each stage. So, \(f_{out} = 1\,\text{kHz}\).
6. \(\text{R}_{\text{A}} + \text{R}_{\text{B}} = \frac{1}{0.693 \cdot f \cdot \text{C}} \approx 144 \, \Omega\); \(\text{R}_{\text{A}} = 72 \,\Omega\), \(\text{R}_{\text{B}} = 72 \,\Omega\), \(\text{C} = 0.001 \,\mu \text{F}\), with a diode across \(\text{R}_{\text{B}}\).
7. For \(\text{V}_{CC} = 5\,\text{V}\): Threshold = \( \frac{2}{3} V_{CC} = 3.33 \,\text{V}\), Trigger = \( \frac{1}{3} V_{CC} = 1.67 \,\text{V}\). \(\text{Duty Cycle} \approx \frac{\text{V}_{\text{control}}}{\text{V}_{CC}}\) ; \(\text{Duty Cycle } (2\,\text{V} ) = 40 \,\% \); \(\text{Duty Cycle } (4 \,\text{V} ) = 80 \,\% \)
8. \(T = 1.1\,\text{RC} = 11 \,\text{ms}\); \(\text{Best-case } (T) = 9.9 \,\text{ms}\); \(\text{Worst-case } (T) = 12.1 \,\text{ms}\) ; \(\text{Variation} = 9.9-12.1 \,\text{ms} \,(\pm 10\,\% \,\text{ error})\).

Copyright © CC BY 4.0 • Contact: sarun@iitism.ac.in