Passive electronic components are components that do not generate energy but can store or dissipate it and require no electric power to operate.
Passive electronic components fall into two categories – dissipative and lossless. Dissipative components cannot absorb power from an external circuit, and lossless components do not have an input or output power flow.
There are many different types of passive electronic components, including diodes and inductors, but resistors, capacitors and transformers are required to build any circuit.
Resistors are passive two-terminal electrical components that reduce current flow in a circuit by implementing electrical resistance. They do this by converting electrical energy into heat, which then dissipates into the air. Through this process, resistors can reduce the voltage levels in a circuit and control the flow of a current to other components; certain components can be damaged or destroyed by too much current.
High-power resistors are capable of generating a lot of heat as the current has to work hard to make it through the resistor. This heat can be utilised in motor controls and generators. Resistors are also key in producing the heat in heating elements that you find in electric kettles, showers, toasters and other appliances.
Variable resistors can be used to adjust settings, such as volume controls on audio devices and televisions or the brightness on dimming lamps. Turning down the volume on one of these devices actually increases the resistance in a variable resistor in a circuit that takes the current to the speaker system.
Like resistors, capacitors are also passive two-terminal electrical components. However, the purpose of a capacitor is to store energy electrostatically between two plates separated by an insulator. When a capacitor is connected to a circuit, it begins to gain an electric charge; one plate gains a positive charge and the other gains an equal negative charge.
Capacitors can be discharged to release energy and power certain devices, like an electric motor or a flashbulb, by connecting them to a second circuit. They can also be used as timing devices, filters, for tuning and for smoothing the voltage in a circuit. Capacitors are widely used in many common electrical devices such as audio systems and televisions.
Transformers are lossless passive electrical components that transfer energy between two or more circuits and also change the voltage between those circuits. When a fluctuating current passes through a wire, a magnetic flux is created around it. This creates an electric current in the other wire coils within the magnetic field.
The overhead electricity lines that you see all over the country carry a huge voltage from electricity pylons. Therefore, to power the devices in our homes, they have to use transformers to drastically reduce that voltage so that the devices don’t short circuit and explode.
Transformers are used in many common electronic devices, such as chargers for phones and laptops and plugs for many household appliances. This is because they all require different voltages to work, and the voltage running through domestic power points is usually much higher than any of these devices need.
Hopefully this definitive guide to passive electronic components has been informative! If you’re currently looking for any of the above, you can browse our passive components.