The two basic types of electronic components are passive and active. Active components require extra power to function; passive do not. For example, a passive component is like a "keyed" ignition switch in a car; an active component is like a remote car starter that needs a second, smaller battery to work. Most electronic circuits contain both active and passive components and power supplies are designed accordingly.
Most active components are semiconductors that operate by "taking" a small amount of power from the circuit power source. Within a semiconductor, a barrier divides positively- and negatively-charged particles. That barrier has to be "broken" for charged particles, or electricity, to flow. A small amount of voltage, called a "bias" voltage, is needed to break the barrier and turn the semiconductor "on."
The diode acts like an electronic switch and is the simplest form of a semiconductor. When the diode turns "on," electricity flows; when it turns "off," electricity is blocked. For on/off operation, the diode requires a 0.7V bias to break the internal barrier. For instance, when a 5V level is provided to the diode, the diode uses 0.7V, and 4.3V is left for circuit consumption.
Typically, anything that doesn't require a bias voltage is a passive component. In other words, any component that isn't a semiconductor is passive. Passive components just have to be connected in the proper circuit pathway to function properly. Common examples of passive components are resistors, capacitors, inductors and transformers. Often, passive components are referred to as "analog" components.
Active and Passive Combined
In general, active components require a bias voltage to break the internal barrier and turn them "on." Common examples are diodes, LEDs, transistors and integrated circuits, or chips. These components are sometimes referred to as "digital" components. In most circuits, passive components are combined with active to provide efficient and safe circuit operation. For example, resistors are often connected to pins of an integrated circuit to limit incoming current.
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