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Introduction to DC Circuits

The field of electronics is very broad, and applies to many aspects of our everyday life. Every radio, television receiver, VCR, and DVD player is electronic in design and operation. So are modern microwave ovens and toaster ovens. Even conventional ovens now include electronic sensors and controls.
Beyond that, however, are even simpler devices that are still electronic in nature. For example, a recent development is the laser pointer, which is essentially a specialized flashlight — and both of these are rather basic electronic devices.
Nor are electronic devices all that new in most households. The telephone system, including standard telephones, is a widespread electronic network designed to be rugged and reliable, with only very simple electronic components. This has changed in more recent years, as more sophisticated electronic devices and methods have enabled improved performance, but the fundamental nature of the telephone system is still pretty much the same.

DC Circuits

Within electrical engineering, a DC circuit (Direct Current circuit) is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors. In this case, the circuit voltages and currents are constant, i.e., independent of time. More technically, a DC circuit has no memory. That is, a particular circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives.


If a capacitor and/or inductor is added to a DC circuit, the resulting circuit is not, strictly speaking, a DC circuit. However, most such circuits have a DC solution. This solution gives the circuit voltages and currents when the circuit is in DC steady state. More technically, such a circuit is represented by a system of differential equations. The solution to these equations usually contain a time varying or transient part as well as constant or steady state part. It is this steady state part that is the DC solution. There are some circuits that do not have a DC solution. Two simple examples are a constant current source connected to a capacitor and a constant voltage source connected to an inductor.


In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered.


Basic Electronic Components

All components used in electronic circuits have three basic properties, known as resistance, capacitance, and inductance. In most cases, however, one of these properties will be far more prevalent than the other two. Therefore we can treat components as having only one of these three properties and exhibiting the appropriate behavior according to the following definitions:

• ResistanceThe property of a component to oppose the flow of electrical current through itself.
  
  
  CapacitanceThe property of a component to oppose any change in voltage across its terminals, by storing and releasing energy in an internal electric field.
  
  
  InductanceThe property of a component to oppose any change in current through itself, by storing and releasing energy in a magnetic field surrounding itself.

As you might expect, components whose main property is resistance are called resistors; those that exhibit capacitance are called capacitors, and the ones that primarily have inductance are called inductors.

Attached Files

DC Circuits, Practical Problems (www.bzupages.com).ppt (411.5 KB, 409 views)

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