178 TIME-DEPENDENT CIRCUIT ANALYSIS
- Expressing pulses in terms of step and impulse functions.
- Laplace transformation method of solving differential equations.
- Time-domain networks and transformed networks in frequency domain for network
analysis. - Network transfer functions.
- Frequency response of networks.
- Low-pass and high-pass filter circuits.
- Bode diagrams and asymptotic Bode plots.
- Two-port network parameters.
- Block diagram representation of simple systems.
- Transient analysis, ac analysis, and frequency response using PSpice and PROBE.
- Use of MATLAB in circuit simulation.
3.8 PRACTICAL APPLICATION: A CASE STUDY
Automotive Ignition System
Ignition systems in automobiles have been designed as a straightforward application of electrical
transients. Figure 3.8.1 shows a simplified ignition circuit for an internal-combustion engine.
The primary inductance, current-limiting resistance, and capacitance form an underdamped series
RLCcircuit. Thus, when the points open, an oscillatory current flows through the primary, thereby
inducing the required voltage in the secondary. The points form a switch, which opens and closes
as the engine rotates, exactly at the instant when an ignition spark is needed by one of the cylinders.
During the period when the points are closed, current builds up rather slowly in the primary
winding of the coil, which consists of a pair of mutually coupled inductors, as shown in Figure
3.8.1. The current is interrupted rapidly when the points open. The resulting large rate of change
of current induces a large voltage across the coil secondary, which is connected to the appropriate
spark plug by the distributor.
The resistance limits the current in case the engine stops with the points closed. Since the
voltage across a capacitance cannot change instantaneously, the capacitor prevents the voltageCondenser PointsPrimary SecondaryCoil
(Mutually coupled
inductors)DistributorSpark
plug12 V+−Figure 3.8.1Simplified ignition cir-
cuit for an internal-combustion en-
gine.