Which components have polarity? Can you answer this question correctly? Please see the standard answer...

Q: How do I determine if a component has polarity?

We are often asked whether certain components have polarity, and this is not always obvious. This article will share some practical experience with you around some common components that are often asked whether they have polarity.

In an electrical context, polarity is defined as the direction in which current flows in a circuit. In a DC system, there is likely to be a positive terminal and an electrically neutral point called ground, which is the 0V point. There is a bipolar DC system that has both positive and negative voltage sides. By convention, DC current flows from the positive terminal to the negative terminal (or ground). Electrons move in the opposite direction. The polarity of AC is not always consistent, as the polarity often fluctuates between positive and negative at a frequency of 50 or 60 Hz.

However, for some reason, things can be a little less clear when it comes to the components of electrical systems. Let's start with the passive components we often ask about, such as resistors.

In electrical analysis, people often assume resistors have polarity to make it easier to intuitively understand the flow of current when designing. I think this practice often leads people to believe that resistors must have polarity. In reality, a resistor can be thought of as a very powerful wire with a specific power rating and resistance. The physical properties of a resistor are entirely determined by the materials used inside it, and its function is to hinder or reduce the flow of current in both directions. Therefore, basic resistors of any type are non-polarized in terms of design, construction, and physical properties.

The second most frequently asked component is the inductor. Inductors are somewhat similar to resistors, except they are specialized for storing electrical energy in the form of magnetic energy. An inductor can be simplified to a fancy coil of wire wrapped around a ferromagnetic material (or other magnetic material). For reasons of physics, design, and construction, an inductor, like a resistor, does not care how it is placed. So I think the confusion comes from analytical practice and certain applications where polarity must be considered when it comes to the direction of current flow. Even though an inductor has no polarity, the specific direction of current flow will change the magnetic polarity in and around the inductor. For example, the coil on a relay has specific polarity markings on the circuit diagram, but this is only to indicate the direction of current flow to properly trigger the relay, and does not mean that the coil itself is polarized. Magnetic polarity can be affected by electrodes, but it is a completely different concept.

Capacitors are a little more complicated when it comes to polarity. The dielectric material in the capacitor and the overall design of the capacitor determine whether it has polarity. For example:

• Aluminum electrolytic capacitors : These capacitors are almost always polarized unless the datasheet or parameters specifically say if they are bipolar. The same is true for aluminum polymer capacitors .

• Ceramic capacitors : non-polar; I have never seen a case of polarity .

• Film capacitors : They appear to be non-polarized, but if you are unsure, check the datasheet. The manufacturer will usually indicate if a component has polarity, as this is critical for applications that require polarity. If the datasheet does not explicitly state this (based on the datasheets I have seen), then it is likely non-polarized .

• Tantalum capacitors : They are inherently polarized parts and will be damaged by reverse voltage .

• Mica capacitor : generally non-polar .

• PTFE Capacitors : These capacitors technically have a thin film design and therefore also tend to be non-polarized .

For any other type of passive component, if the polarity is not explicitly stated, then there is most likely no polarity. Switches and metal contacts are not polarity related at all, as everything is mechanical and metal conducts electricity regardless. Polarity is the type of property that can make or break a component and/or design, and therefore must be included in the datasheet. An example of such a component is a reed switch, which is basically just a simple electromechanical switch with a simple metal contact moved by a magnetic field, and therefore has no polarity

Active components almost always have polarity because they require power to operate.

However, depending on the type of active device, the direction of the current may not be of concern in some aspects (such as input and output). Active devices are much more complex than passive components, so if you have questions about such components, it is recommended to read the data sheet of the corresponding product.

Here are some examples of active devices:

• Diodes : Typically polar components, depending on the type (Zener diodes are a special case, they can be bipolar, depending on the voltage).

• Transistor : For power supply, it has polarity because a specific positive or negative source is required; for conducting current, it depends on the type and mode of transistor used.

• AD-DC converter : Input is bipolar; output can be unipolar (all positive or all negative voltages and ground reference, or bipolar, i.e., bidirectional positive and negative voltage outputs with ground reference). Power supplies are inherently polar.

• Crystal Oscillators/Resonators : If the crystal/resonator is a two pin version, they are usually non-polarity sensitive and can be powered either way. For multi-pin versions, always check the datasheet.