Question 15.10: Objective: Design a 555 IC as a monostable multivibrator to ...
Objective: Design a 555 IC as a monostable multivibrator to produce a specified output pulse width.
Specifications: The circuit with the configuration shown in Figure 15.40 is to be designed to produce an output pulse width of 100 µs.
Choices: A 555 circuit is available. The final design is to use standard-valued elements.
Consider the circuit in Figure 15.40. Let C = 15 nF.
Using Equation (15.95), we find that
T = RC \ln(3) = 1.1 RC (15.95)
R = \frac{T}{1.1C} = \frac{100 × 10^{−6}}{(1.1)(15 × 10^{−9})} ⇒ 6.06 k\Omega
Trade-offs: Using standard-valued element values of C = 12 nF and R = 7.5 kΩ will produce an output pulse with a width of 99 µs. Element tolerances also need to be taken into account.
Comment: To a very good approximation, the pulse width is a function of only the external resistor and capacitance values. A wide range of pulse widths can be obtained by changing these component values.