Active components can control, switch, rectify, convert, or amplify a signal using an active device function. For power gain, they draw energy from a source other than the input signal. Passive components require no energy source beyond the input and cannot provide power gain. They dissipate, store, release, or transfer energy.
The test is not simply whether a part has voltage across it or whether current flows through it. Power gain and the source of energy are the useful dividing properties. Semiconductor diodes are the important convention-based exception, explained below.
Active vs Passive Components Comparison Table
| Criterion | Active component or element | Passive component or element |
|---|---|---|
| Distinguishing property | Can control, switch, rectify, convert, or amplify a signal using an active device function | Contributes resistance, capacitance, inductance, interconnection, or another passive function |
| Energy source | For gain or controlled output power, draws energy from a source other than the input signal | Requires no energy source other than the input |
| Power gain | An active stage can deliver more signal power at its output than it receives from the input signal | Cannot provide power gain |
| What happens to energy | Controls or converts supply energy | Dissipates, stores, releases, or transfers input energy |
| Typical examples | Transistors, operational amplifiers, ICs that provide gain or switching, semiconductor diodes, and independent sources | Resistors, capacitors, inductors, transformers, and integrated passive filters |
Classified List of Active and Passive Components
| Component | Classification | Reason |
|---|---|---|
| BJT or MOSFET | Active | Switching and gain are active functions. A control signal can govern energy drawn from a supply. |
| Operational amplifier | Active | It uses supply energy and can provide signal gain. |
| Semiconductor diode | Active in IEC semiconductor classification | IEC includes diodes because rectification is an active function. An ordinary diode does not provide power gain. |
| Independent voltage or current source | Active circuit element | It can supply energy to a circuit. |
| Resistor | Passive | Its circuit function is resistance, and it provides no power gain. |
| Capacitor | Passive | Its circuit function is capacitance. It can store and return energy but does not create net energy. |
| Inductor | Passive | Its circuit function is inductance. It can store and return energy but does not create net energy. |
| Transformer | Passive | It transfers electrical power and can change voltage or current, but it does not provide power gain. |
For semiconductor parts, this page follows IEC 60747-1:2006+A1:2010. For circuit passivity, it follows the energy-based definition in IEC 60050-131.
How to Classify Active and Passive Components
Use the component's circuit function, external energy source, and ability to provide power gain. Do not sort only by the number of terminals, semiconductor material, voltage change, or whether current happens to flow.
- Identify the function. Resistance, capacitance, and inductance are passive functions. Rectification, switching, and gain are active functions under IEC semiconductor terminology.
- Trace the energy. An amplifying active stage uses a separate supply. A passive network has no energy source beyond its input.
- Check power gain. Voltage gain alone is not enough. The question is whether output signal power can exceed input signal power by using supply energy.
- Name exceptions. State the chosen convention for diodes, sources, and mixed devices instead of forcing them into an unexplained list.
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Active Components and Active Elements
Transistors and operational amplifiers are clear active examples. Their input signal controls output energy drawn from power rails, which allows switching or power gain. The 2N2222 transistor guide shows a discrete NPN switching and amplifying device. The TL072 pinout guide covers a powered operational amplifier.
Most integrated circuits contain active devices and perform gain, switching, conversion, or control, so those ICs are active. An IC is not active merely because its elements share a package. An IC whose functions are limited to resistance, capacitance, inductance, or passive filtering, with no separate supply or power gain, is passive. The TI TPD6F002 combines passive C-R-C filtering with a TVS diode array. Under the IEC convention used here, those semiconductor protection diodes are active elements, so this part is a mixed device and a poor test case for calling an IC passive.
Light-emitting or light-sensing semiconductor devices perform active semiconductor functions under IEC 60747-1. Independent voltage and current sources are active circuit elements for a different reason: they supply energy to the circuit.
Passive Components and Passive Elements
Resistors, capacitors, and inductors contribute the passive functions named in IEC 60747-1. A resistor dissipates input energy. Capacitors and inductors can store energy and return it later, but that does not create net energy or power gain.
A transformer is also passive. It can step voltage up or down and change the available current, but it transfers electrical power rather than adding power from another source. The simple parallel circuit guide shows how passive branches share voltage and divide current.
Edge Cases That Break Shortcut Rules
Short definitions often fail on the same four cases. The correction column shows which property actually decides the classification.
| Case | Misleading shortcut | Correct classification |
|---|---|---|
| Diode | It has no power gain, so it must be passive. | IEC semiconductor terminology includes a diode as active because it performs rectification. State the convention instead of hiding the exception. |
| Transformer | A higher secondary voltage means amplification. | A transformer can have voltage gain without power gain. It transfers input power and remains passive. |
| Battery or ideal source | Only amplifying devices are active. | A source is an active circuit element because it supplies energy. It is not an amplifying semiconductor component. |
| Sensor | Every sensor belongs to one class. | Classify the actual implementation. A resistive sensing element contributes resistance, while a powered sensor IC performs active functions. |
Circuit Symbols of Active and Passive Electronic Components
Schematic symbols identify the component or circuit function. Classification still follows that function, its energy source, and whether it can provide power gain.
| Symbol name | Component represented | Classification criterion |
|---|---|---|
| Diode symbol | Diode | Active under the IEC semiconductor convention used here, although an ordinary diode provides no power gain. |
| Capacitor symbol | Capacitor | Passive because its circuit function is capacitance. |
| Inductor symbol | Inductor | Passive because its circuit function is inductance. |
| Resistor symbol | Resistor | Passive because its circuit function is resistance. |
| Voltage source symbol | Independent voltage source | Active as a circuit element because it can supply energy. |
| Logic gate symbol | Logic gate or gate circuit | Active when its powered devices switch or control a logic signal. |
| Coil symbol | Coil or winding | Passive when its circuit function is only inductance. |
| Regulator symbol | Voltage regulator | Active when it uses input or supply energy to control the output voltage. |
| Transformer symbol | Transformer | Passive because it transfers input power without providing power gain. |
How Active and Passive Components Work Together
Most useful circuits combine both classes. An amplifier may use an active transistor or operational amplifier with passive resistors and capacitors for bias, feedback, filtering, and stability. A power supply provides the energy that lets the active stage control a larger output signal.
A passive network can attenuate, filter, divide, store, or transfer a signal without power gain. Adding an active device and a supply can provide buffering, switching, oscillation, or amplification. Classify each component by what it contributes to that specific circuit.
Summary
Active components perform functions such as rectification, switching, conversion, and gain. An amplifying active stage uses supply energy so its output signal can have more power than its input signal. Passive components use only input energy and provide no power gain.
Resistors, capacitors, inductors, and transformers are passive. Transistors and operational amplifiers are active. Semiconductor diodes are usually classed active under IEC semiconductor terminology even though an ordinary diode provides no power gain. A transformer remains passive even when it raises voltage.
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