Assignment 7
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The document describes several circuit analysis problems involving bistable and astable multivibrators. It asks the reader to: 1) Derive expressions for threshold voltages in bistable circuits and calculate component values to achieve given thresholds. 2) Sketch transfer characteristics for different bistable and astable circuits. 3) Calculate oscillation frequency for an astable multivibrator circuit. 4) Design circuits to produce square waves of given amplitude and frequency.
Assignment 7
- 1. Assignment-7 Bistable and Astable Multivibrators IEC103 Date: 20/03/13 1. Consider a usual inverting bistable multivibrator circuit with the op-amp’s non-inverting input terminal connected to a positive voltage source V through a resistor R3. a.Derive expressions for the threshold voltages VTL and VTH in terms of op-amp’s saturation levels and , R1, R2, R3 and V. b.Let = =13 V, V= 15V and R1 = 10kΩ. Find the values of R2 and R3 that result in VTL = +4.9V and VTH = +5.1V. 2. Consider a non-inverting comparator circuit with op-amp’s negative input terminal disconnected from the ground and connected to a reference voltage VR. a.Derive expressions for the threshold voltages VTL and VTH in terms of the op-amp’s saturation levels and , R1, R2 and VR. b.Let = = V and R1 = 10kΩ. Find R2 and VR that result in threshold voltages of 0 and V/10. 3. Consider the circuit in figure 1. Sketch and label the transfer characteristics VO – VI. The diodes are assumed to have a constant 0.7 V drop when conducting, and the op-amp saturates at ±12 V. What is the maximum diode current? Suppose that R1 is eliminated and R2 is short circuited. Sketch the transfer characteristics VO – VI. Figure 1
- 2. 4. Consider a bistable circuit having a non-inverting transfer characteristic with = = 12V. VTL = -1V and VTH = +1V. a.For a 0.5 V sine wave (0.5 V is its amplitude) having zero average, what is the output? b.Show the output if a sinusoid of frequency f and amplitude of 1.1 V is applied at the input. By how much can the average of this sinusoidal input shift before the output becomes a constant value. 5. Consider an astable multivibrator circuit shown in figure 2. Find the frequency of oscillation for R1 = 10kΩ, R2 = 16kΩ, R = 62kΩ and C = 10nF. Figure 2 6. Consider the circuit shown in figure 3. Design the circuit to have an output square wave with 5V amplitude and 1kHz frequency using a 10nF capacitor C. Use β = 0.462 and design for a current in the resistive divider approximately equal to the average current in the RC network over ½ cycle. Assuming ±13V op-amp saturation voltages, average that the zener operates at a current of 1mA. Figure 3
- 3. 7. Consider the circuit in figure 4. The circuit consists of an inverting bistable multivibrator, with an output limiter and a non-inverting integrator. Using equal values for all resistors except R7 and a 0.5nF capacitor, design the circuit to obtain a square wave at the output of the bistable multi- vibrator of 15V peak to peak amplitude and 10 kHz frequency. Sketch and label the waveform at the integrator output. Assuming ±13 V op-amp saturation levels, design for a maximum zener current of 1mA. Specify the zener voltage required and give the values of all resistors. Figure 4