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What is PCB relay – basics and analysis


What is PCB relay?

A print relay, also known as a “PCB relay,” is designed to be attached to a printed circuit board. The PCB relay connects various electronic components electrically by having conductive tracks, pads, and other features cut from at least one layer of copper laid on or between layers of a nonconductive substrate. PCB relay is smaller relays that can be mounted directly on PCBs. Due to their size and weight, these relays are suitable for through-hole component mounting on a circuit board. They typically have high voltage ratings.

A relay is used when it’s necessary to control a circuit with a high voltage and a low-power circuit after it. While relays do not provide galvanic isolation, semiconductor-based exchange does. PCB relay is functionally equivalent to other relays despite being physically smaller and occasionally having lower voltage ratings. PCB relay with a restricted number of connections is available in a variety of mounting levels and contact materials. PCB relay, which are also called module or print relays, are used to isolate circuits from each other, translate signals, and boost signals. 

The components of PCB relay

Relay types that may be utilized in PCB relay circuits include reed, electromagnetic, solid-state, and thermal relays. An electromagnet in a typical DC or AC electromagnetic PCB relay absorbs the electrical information and converts it into the precise action of shutting or opening the circuit.

○Armature, coil, and contacts are often seen in PCB relay.
○In reed PCB relay, A glass tube that is sealed and contains the reeds and contacts is the exterior of a reed relay, which is also surrounded by a coil.

The function of PCB relay

This microscopic PCB relay is equally as valuable as their bigger standard sized ones, despite the fact that they are smaller and can only tolerate lower voltages.
The following operations often rely on the type:

★HIGH VOLTAGE SWITCHING: these mechanical electro-instruments assist in converting high-frequency signals into signals with high voltage. High currents and voltages are no problem for them.

★PROTECTION OF OVER-CURRENT: PCB relay that prevent a circuit from overheating or flowing too much current in the incorrect direction.

★COVERAGE OF THERMAL: these relays activate when the temperature rises over a specified level.

★DIFFERENTIAL PROTECTION: when the currents or voltages of two distinct circuit components vary, these relays switch on.

★COVERAGE OF FREQUENCY: when the frequency of the alternating current is too high or too low, these relays shut off.

★TIME-LAG: these relays only function for a certain period of time.

★SEMI-CONDUCTOR: these PCB relays are controlled by electronics.

How a PCB relay works?

The magnetic circuit develops an air gap when the PCB relay is switched off. As a result, two sets of contacts are shut while the third set remains open. However, it is crucial to understand that a relay’s number determines how many contact sets are present. The PCB relay typically operates by running an electric current through the coil, creating a magnetic field. The relay’s armature makes, or breaks contact with a static contact when it is turned on. The connection will be severed if the relay’s power is switched off while the contacts are closed. 

The reverse is true when things are flipped around.The armature returns to its relaxed, initial state when the coil’s current is cut off. The spring provides the force that pulls the armature back when using industrial motor starters. Additionally, gravity has an impact. Almost all PCB relay is designed to operate rapidly. In low-voltage applications, it reduces noise, while in high-voltage PCB, it prevents arcing.

Steps for design a PCB relay

In order to make smaller devices possible, electromagnetic relays that may be attached directly to a printed circuit board have been created (PCB relay). Smaller relays do exist, but they still need to be prepped by being heated, soldered, and cleaned. The performance of an electromagnetic relay will suffer if the mechanism within is broken. PCBs may have relays installed if they are 1.6 mm thick and made of glass-epoxy or paper-epoxy.

All PCB relays need a conductor thickness of 35 mm to 70 mm. Electromagnetic and thermal relays have contrasting responses to magnetic fields and temperature, respectively. When designing a printed circuit board (PCB), be sure to provide enough space between relays and other devices, such as transformers and semiconductors, that might generate heat. Relays need to be protected against stress and vibration in the product’s construction. When the relay is put in place, vibrations and shocks should be kept away from the moving armature.

♥First, remove the relay’s PVC or plastic casing with a screwdriver.
♥It shows relay components (spring, armature, coil, contacts, and yoke).
♥PCB relay circuits require the proper relay and flawless installation.
♥A spring tightens the relay when it’s off, allowing air to flow through the magnetic circuit.
♥One or two relay sets are closed while the other is open.
♥Different relays have fewer or more contact sets depending on their use.
♥A wire connects the movable PCB contacts to the armature via the yoke.
♥Solder attaches relay to circuit board.
♥When the relay’s power is turned off, an air gap forms in the magnetic circuit, causing two sets of contacts to close while the other set remains open.
♥Relay value determines the number of contact sets.
♥A relay’s coil sends an electric current, creating a magnetic field.
♥When activated, the relay’s armature contacts a static contact.
♥If the relay’s power is cut while the contacts are closed, the connection is severed.
♥Flipping things is opposite.

How to mount electromagnetic relay on PCB?

Be sure of the electromagnetic relay’s type before trying to mount it on a printed circuit board. It may be sealed, unsealed, or a flux-protection relay. The only method to deal with unsealed relays is to prevent flux or cleaning solvents from getting into the internal workings since they must be hand-soldered and cannot be cleaned by immersion in liquid.

Lifting the terminals off the PCB and moving the contacts away from the base is a good idea before installing an unsealed relay. Flux and cleaning agents cannot enter the housing since the relay is shut. Flux-protection relays are designed to keep flux outside of the relay’s housing, similar to sealed relays. The connection of the flux protection relays to the PCB prevents them from being submerged in water for cleaning.

The coil in PCB relay

The element responsible for the device’s functioning on the main side of a PCB relay is the magnetic, coil, or motor unit. It has all the parts needed to change the electrical energy flowing from the primary side into the mechanical force needed to move the contacts and switch the secondary circuit.Anytime a current flow through the coil of a PCB relay, the coil is converted into an electromagnetic field, and an electromagnet is produced.

The force of the magnet causes a switch to be pushed to the left, and this movement brings together the spring contacts and completes the circuit to which they belong.Also, when a voltage is applied to the coil’s terminals, the magnetic field and magnetic flux are created by the current flowing through the coil. The amount of current flowing through the coil and the number of times it is coiled together are two of the main variables that affect the magnetic field or flux strength.


PCB relay for the circuit are crucial parts of the security system. They carry out the same tasks as the standard sized ones despite their smaller stature. However, you must proceed with great care while connecting them to a circuit board.

To make sure the PCB relay works, you must also keep in mind the above PCB design requirements. Every designer must be knowledgeable about all of the constituent parts that make up PCB relay since they are such a crucial component of printed circuit boards. Before building a PCB, you should think about the relays on the board (PCB Relay).



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