What is polarity
If you know one thing about batteries, it’s that they have one positive and one negative terminal (or pole). When connecting the battery, the positive side goes to the positive side of a device. Likewise, the negative goes to the negative. The energy won’t flow through the circuit if it’s connected the opposite way. Some components work similarly. But why is that? Because of something called polarity.
Before talking about polarity in more detail, we have to first go over the current direction. The conventional current flows from the positive pole to the negative. Electrons flow in the opposite direction, from the negative pole to the positive.
When working with electronic circuits, only the conventional current is shown. All descriptions use it. If you see an arrow depicting current flow, you know for a fact it’s the conventional current flow.
In a direct current (DC) circuit, the current flows in one direction only. One pole is always negative while the other is always positive. In an alternating current (AC) circuit, these poles change from negative to positive and vice versa routinely.
What is polarity?
In the simplest terms, polarity indicates the symmetry of a component. It is a directional flow of electrons from one pole to the other. Hence, the name. The components are either polarized (with polarity) or non-polarized (without polarity).
Non-polarized components are as simple as they get. They can be connected either way and will work correctly. It is uncommon for them to have more than two terminals. Every terminal on a non-polarized component is equal.
Polarized components can be connected only one way in a circuit for them to work. The current must go from anode to cathode (from the positive pole to the negative). If the current goes the other way, at best it will just stop the circuit. At worst, it could result in sparks and burned components. Polarized components can have a minimum of two pins and over one thousand. Every pin is unique. They each have a designated position where they go. If they aren’t connected correctly, some of the mentioned issues might happen.
But how would someone identify which pole is positive or negative? If there is a constant voltage between two points, one of them will have more electrons than the other. The pole with more electrons has negative polarity. The other one, then, has positive polarity. If those two points are connected with a conductive path, the electrons flow from one pole to the other. This is what we call an electric current.
When polarity needs to be identified on a schematic or a diagram, the polarity symbols are used. The positive pole is usually marked with the color red or a plus symbol. The negative pole is most commonly marked with the colors black or blue and a minus symbol. Other color schemes are sometimes used in different industries, like automotive and telecommunications.
The term polarity is used in electronic signaling, electricity, and magnetism. It is a crucial concept to understand before seriously working with electronics. You won’t be able to solder components to a PCB or plug them into a breadboard if you don’t understand it. Knowing how to identify polarized components is essential before any of that.
Let’s go over the most common components to learn how and recognize polarized components and connect them properly.
A resistor is a component you’ll be using the most. It doesn’t have polarity so you don’t have to worry about how you connect it. This is true for both THT and SMD resistors. Imagine it like a bumpy road. No matter the side you come from, it will be bumpy. No matter which side the current comes from, the resistance will be the same.
You’ll want to use an appropriate resistor for the circuit, though. Too strong of the resistor will block current from reaching all components. If it’s too weak, there is a chance of components frying due to excessive current.
Depending on the material, capacitors can be polarized or non-polarized. Non-polarized THT capacitors commonly have blue or yellow ceramic bodies.
Non-polarized SMD capacitors look like tiny, two-colored metal bricks. They don’t have any markings on them to indicate terminals.
Diode & LED
A diode is a two-terminal component that allows current flow in only one direction. It is always polarized. The positive pole is called the anode, and the negative cathode. Current flows through the anode to the cathode. The diode’s sibling, the LED (light-emitting diode) , is not too different. The main difference is that LED emits light, as the name suggests.
Since both diode and LED are polarized, there is a need for differentiating the anode and cathode. On a regular THT diode, the cathode is marked with a colored band at the end. The 1N4007 diode is pictured below. As you can see, the cathode is on the left, indicated by the silver band.
SMD diodes similarly indicate cathode. The line indicating cathode can be of various thicknesses, but it is always on the cathode side.
The LED indicates the cathode a little differently. Instead of a colored band, the cathode pin will be shorter on the LED. Since you can’t see this when the LED is soldered or on a breadboard, the case will be slightly cut off on the cathode side. This might be a bit hard to notice at first, but once you see it, you’ll have no trouble finding it in the future.
SMD LEDs similarly indicate the cathode – one corner will be slightly cut off.
If you don’t connect the battery correctly, it won’t matter if you connect polarized components properly. Batteries are polarized, so regardless of which one you use, you need to connect it correctly.
If you replaced batteries, you know how to find their polarity. Most of them will indicate the positive terminal with a plus symbol, and the negative with a minus symbol. Some batteries might have wires. The red wire will indicate the positive terminal, and the black or blue wire will indicate the negative terminal.
As mentioned, capacitors can be either polarized or non-polarized. THT electrolytic capacitors (those that look like little tin cans) are polarized. The negative terminal is usually marked with a minus symbol on the side. The cathode pin is also usually shorter than the anode.
Be very careful when connecting the electrolytic capacitor. If it’s not connected correctly, it will end up in smoke, becoming useless. It might even explode ! Before plugging your circuit with capacitors into a power source, make sure everything is connected correctly.
Similar to SMD diodes, SMD capacitors have a line on the side indicating a terminal. Unlike diodes that have a line indicating cathode, the capacitor’s line indicates anode.
Integrated circuit (IC)
A single integrated circuit can contain hundreds of pins, each with its function. Just like electrolytic capacitors, it is important to pay attention to an integrated circuit’s polarity. Otherwise, it will most likely burn, melt, and become completely unusable.
An integrated circuit will usually have a notch or an etched dot to indicate the first pin.
Check the datasheets
Among the many components available, these are just a few examples. Knowing the polarity of the components allows you to prevent damage.
Some non-polarized components can be packaged in polarized packages. Most components will indicate whether they are polarized or not. You should always check the datasheets if you’re unsure of the component’s polarity.
When working with components, it is also important to know whether they are active or passive. If you’re interested in building some projects, check our tutorials page . We regularly update it with new tutorials and projects.
Products used in this tutorial
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