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What Is PCB Relay ?

Plenty of circuit processes happen in a specific printed circuit board. It can range from transmission and reception of data, electricity transmission, to communication, etc., based on the type of printed circuit board. Therefore, as a PCB designer or enthusiast, it helps to understand the different PCBs and the PCB relay activities in a circuit. You will not only develop an appropriate PCB for the intended device but ensure that circuit.

Printed Circuit Board Relays

What do you picture with athletics relay activity? Well, relays in circuit boards imply an electrically ran switch, which proves crucial in the proper functioning of PCBs and devices. PCB relay circuits can include a diverse range from reed and electromagnetic to hybrid, thermal, and solid-state relays. A typical DC or AC electromagnetic relay comprises an electromagnet, which receives and converts the electrical signal into the mechanically inclined action of closing and opening the circuit. Besides this, a relay circuit board will typically include an armature, coil, and contacts.

The electromagnetic PCB relay works by applying an electromagnetic field when power gets applied to the coil, subsequently causing the movement of the armature and making the contacts either close or open. PCB relays get classified by construction, mounting type, or function. Consequently, you will get examples of relays such as PCB mount relay, PCB relay 12v, etc.

If you want to buy printed circuit board relays or want to inquire about them, do not look beyond us at RayMing PCB and Assembly Company. You will get incredibly useful information on PCB relays and details on how to order them at a cost-effective price. Further, you can also get information on printed circuit boards.  

Crucial Details about PCB Relays

relay circuit board
  • Design and components of PCB relay. If you want to make a PCB relay, it becomes vital to remove the relay’s PVC or plastic case using your screwdriver. It will allow you to view the relay parts (spring, armature, coil and contacts, and yoke).  A PCB relay circuit requires the perfect relay and a seamless mounting process to ensure efficient functioning. Because of this, you have to hinge the armature on the yoke and link it mechanically to a single or more moving contact. The relay gets held snugly by a spring, creating an air gap within the magnetic circuit when the relay gets de-energized. Consequently, a set or two of contacts within the relay get closed while the other gets open. However, other relays might have fewer or more contact sets based on their utility.  It also possesses a wire connection between the yoke and the armature, ensuring circuit continuity between the PCB’s moving contacts of the circuit track and armature through the yoke. The relay gets soldered on the printed circuit board.
  • How a relay works
  • As earlier stipulated, the de-energizing of the relay, the magnetic circuit forms an air gap, forcing the two contact sets to close while the other remains open. However, it becomes crucial to note that other relays may have fewer or more contact sets based on their utility. The relay often works through the application of electric current that, when passed through the relay’s coil, generates a magnetic field. It activates the relay’s armature, which breaks or makes a connection with a static contact. Whenever the de-energization of the relay occurs when the contacts are closed, then this movement opens the contacts instead, and the connection breaks. The opposite happens when the situation gets reversed.    

The withdrawal of the current from the coil ensures the return of the armature to its original and relaxed position. While the force that returns the armature gets provided by the spring, gravity also gets applied in instances that involve motor starters of an industrial nature. Most relays by design get manufactured to function fast. In low-voltage applications, it reduces noise, while in high-voltage situations, it limits arcing.

Whenever the coil gets energized with current, it becomes crucial to diode diagonally on the coil. It will dissipate the energy emanating from the disintegrating magnetic field upon deactivation, which would generate a spike in voltage that can hamper the components in the semiconductor.

  • Relay’s pole and throw. Relays operate as switches, and therefore, a similar terminology applies in relays as it does in switches. A relay will switch at least a single-pole, with its contacts getting can getting be-thrown through the energization of the coil. Energization of the coils can happen in one of three ways, which entail the following.
  • NO or Normally-Open contacts complete the circuit whenever the relay gets activated and deactivates when the relay gets disconnected. No has diverse synonyms ranging from “Make” contact, “Early-Make,” or “NOEM.” It all implies the contacts closing before fully engaging the switch or button.  
  • NC or Normally-Closed contacts disengage the circuit upon activation of the relay. Please note that the circuit gets connected if the relay proves inactive. It also gets referred to as “Form B contact” or “Break contact.”
  • CO or Change-Over is also inferred as DT (double-throw). The contact controls the two circuits that feature one having open contact and the other with closed contact.

Below some of the crucial designations encountered.

  • SPST. It denotes a single pole single throw and contains two terminals that can get disconnected or connected. When you include two (accounting for the coil), then the relay possesses four terminals overall. In instances where you encounter an SPNC or an SPNO term, understand that this aims to resolve the ambiguity that arises with the pole’s stature (whether closed or open)
  • SPDT. It denotes the single pole double throw. It has one terminal that connects to two one of the other two. If you include the two that account for the coil, the relay has a total of five terminals.
  • DPST. It denotes a double pole single throw. It has two terminal pairs and equates two of the SPST relay or switches actuated through one coil. If you include the two, accounting for the coil, it possesses a total of six terminals.
  • DPDT. It denotes a double pole double throw and has two change-over terminal rows. It equates to two SPDT relays or switches; all actuated through one coil. It contains eight terminals that include the coil.
  • CO or Change-Over Relay (DT or Double-throw relay)
  • It has close similarities to the SPDT relay. Like SPDT, the configuration switches from a single common pole to the other two and flips between them. For instance, when you consider a relay (SPDT) with a single “C” pole, with the others coming as “B” and “A,” Whenever the coil proves inactive, the “C” gets connected to “A” and in a resting point. However, when the relay gets powered, the “C” gets connected to “B” in a resting point. Therefore, the position only proves one of either resting, with the other needing the coil to get powered.  
  • Relay’s current and voltage position. Plenty of relays get availed in diverse operating voltages such as 5, 6, 12, and 24V. Therefore, if the needed operating voltage gets supplied, the relay gets activated. A relay’s operating voltage typically comes in DC while contractors and main control relays operate with AC coils. A relay’s terminal residuals get used to connecting with DC or AC (50/60Hz) circuits. But take note of the fact that contact pins and switching have maximum current and voltage parameters/ ratings. It always gets in-scripted on the relay’s PVC or plastic case. It becomes essential to restrict yourself within these confines when using the relay. However, you can use a higher current whenever the voltage proves lower. But try and avoid overloading the relay to limit damage and burning out of the appliance or circuit connected. Always endeavor to pick a relay that will handle your current and voltage requirements to avoid incidences of burning out your relay coil.
  • Reuse and recycle old relays. It always proves possible to desolder old or existing circuits before resoldering new circuits as relays cannot get burned with excessive soldering. You can also recycle the coil’s windings, and this includes diverse circuits and jumper wires. In addition, you can reuse the screws and contacts, bolts, nuts, and relay washers.

Mounting Techniques and PCB Design Needs for Electromagnetic Relay

It has become apparent that PCB relays play a significant role in consumer electronics, control panels, scientific and medical equipment. Additionally, by now, you have learned about the different types of PCB relays. But how can you mount a PCB relay on a printed circuit board? A PCB relay only becomes crucial when mounted and functioning on the PCB. To understand this better, we detail the mounting techniques involved in relay circuit boards.

Classification of relays by the mounting technique entails surface mounting and discrete mounting techniques. However, this mounting technique often relies on the board type involved.  

When it comes to the printed circuit board design needs for relays, you need to consider a few fundamental aspects, especially on the mounting technique. For instance, when developing smaller electromagnetic relays that have to get soldered on the printed circuit board, you must consider the physical process needs that might affect the mounting process. Some of these requirements include becoming attentive to the heat application, soldering, and washing. It becomes a problem when the physical processes during the mounting process distort the relay’s internal electromagnetic mechanism. In such an incidence, the relay will underperform when measured against its expected standards.


PCB relays prove a crucial aspect of printed circuit boards, and thus every designer has to understand different aspects of these relays. You cannot design a PCB design without taking into account the PCB relay aspects.




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