Electronic components can be classified as passive or active, depending on their function. Electronic components that inject power into circuits, controlling and amplifying the electrical current as it flows through them, are considered active, while those that do not are passive. Further, passive electronic components neither store nor consume energy, while active components do. One simple test determining whether a component is active or passive involves measuring the difference between the input and output signals. If power declines, it indicates a passive component, whereas if the test amplifies the signal, it denotes an active component. All electronic circuits include at least one active component, while most electrical devices have both passive and active electronic components.
What Are Passive Electronic Components?
Those electronic parts that do not control the electrical current from an external source are considered passive and feature two port terminals. Passive components neither amplify nor augment the power signals to the component and are generally categorized as resistors, capacitors, or inductors.
Resistors
These passive electronic components resist electrical signals, featuring two interchangeable leads with material placed between them that restricts current flow. An ohm measures this resistance, with resistors used to control precisely how much current flows through the circuit while also managing voltage levels.
As resistance to electricity flow increases, the current going through the element decreases. Resistors essentially “waste” electricity by making it more difficult for current to flow. This generates heat, as with incandescent light bulbs or filaments in water heaters. Electronic components called variable resistors also use this concept to control the volume on radios, televisions, and many other devices that adjust the sound volume. Instead, they increase resistance to turn down the sound and decrease resistance to turn it up.
Capacitors
Capacitors store and release an electrical charge. Their ability to store a charge is called capacitance, measured in farads. Typically, capacitors come in the form of two conductive plates separated by a dielectric or insulating material. However, it will not work on direct current (DC), as the dielectric blocks it.
Capacitors pass along alternating current (AC), causing the voltage to repeatedly charge and discharge as it alternatively stores and then releases energy. One of their key functions is their ability to pass along AC while blocking DC, also called “AC coupling.” As DC goes into the capacitor, a positive and negative charge builds up on their corresponding plates until the capacitor can hold no more electricity, which stops the current from flowing.
Since AC constantly changes, it keeps the capacitator charging and discharging. While the capacitor’s dielectric does not allow electrons to pass directly through the capacitator, it does allow a displacement current to pass around it. This opposition to the alternating current is known as “capacitive reactance,” which is also measured in ohms.
Inductors
Also called coils, inductors typically use at least one loop of conductive wiring that forms around an iron and steel core, though sometimes these are made from another magnetic material. The current passing through the inductor produces a magnetic field that stores the electricity in an inductance process, measured in henries (H). The electrical current flows through a wire to generate this magnetic field, with the direction determined by the current’s flow. Electronic circuits use inductors to restrict the flow of AC as the direct current passes through them.
Filter Circuits
Filter circuits eliminate unwanted electrical signals while letting signals with specific frequencies pass through. Made from an inductor – which blocks AC and allows DC – and a capacitor – which blocks DC and allows AC, filter circuits also serve an electrical function. They essentially remove AC component in the output to allow the DC component to reach the part of the component using the electrical energy.
What Are Active Electronic Components?
Active electronic components extract power from the outside and deliver it to other components or devices. They can supply energy almost indefinitely until it connects to an external source and controls the electricity as it passes through the circuit. While there are numerous types of active electronic components, they fall into two basic categories: transistors and diodes. Another active electronic component called the thyristor also exists, which is used mainly for high-power applications, including utility substations.
Diodes
Diodes are active electronic components that conduct current in only one direction through an electrical field and keep that current from reversing. Two types of commonly used diodes include:
- Rectifier diodes convert to DC voltage from line voltage, operating at line frequency or limited multiples. In rectification, these diodes make up a rectifier circuit that can convert AC power to DC.
- High-frequency diodes behave like capacitors with reverse bias or variable resistors with forwarding bias. Their high-frequency characteristics mean they can serve various applications, including mobile phones.
Transistors
Transistors feature a control terminal that switches the device from conducting to blocking current and vice versa. While diodes will always conduct when their anode is positive, these active electronic components only conduct electricity when the control terminal is set for conduction.
Transistors have a few basic characteristics:
- Blocking: The only real similarity transistors have to diodes is their polarity. Unlike diodes, they can conduct or block current, depending on the type of control terminal, though can do so only in one direction. Transistors tend to be used primarily in networks that support direct current, while diodes operate mainly with AC circuitry.
- Switching: This transitioning from blocking to conducting state does not occur instantly. When turned on, the transistor’s voltage switches while the current goes from nothing to whatever the load requires. When turned off, the voltage returns to the supply as the current returns to zero.
- Switch mode: Most power circuits operate in switch mode, acting as a switch by turning fully on or off. In limited cases, depending on the application, transistors may operate in linear mode, where the control terminal instead modulates voltage. The voltage across the transistor’s terminals produces the power dissipating as current moves through it. Significant electricity dissipation inside the transistor will occur if the voltage across its terminals is modulated. This energy requires a suitable heatsink. Otherwise, the transistor will fail, so power circuits generally operate in switch mode.
Understanding Differences Between Passive & Active Electronic Components
Understanding the differences between how passive and active electronic components operate also involves comparing how each of these components behaves.
The main differences between passive and active electronic components are:
- Energy source: Active components require additional energy to operate, while passive components require no additional source. Resistors work on their own and require no specified voltage.
- Energy production or storage: While active electronic components produce energy by generating current or voltage, passive components store energy instead, though do so in different ways. For example, capacitors store energy using an electrical field, while inductors store energy using magnetic fields.
- Linearity: Passive electronic components are linear, while their active counterparts are non-linear. This essentially just means that with passive components like resistors the current flowing through the circuit will be directly proportional to the voltage, while with active components like transistors the ratio will vary in respect to voltage and current.
- Power: Active electronic components can produce a power gain while passive parts cannot amplify power.
- Current control: Passive parts cannot control current flow, whereas active electronic components can.
- External source: Active components require an additional energy source to control operations, though passive parts do not require this.
To learn more about passive vs active electronic components, please contact our expert team at Solid State Inc. today!