PCB Transformer: What Is It And Where to Use

This article provides an in-depth exploration of PCB-mounted transformers, which are integral to the design and functionality of printed circuit boards. At OurPCB, we sell PCB transformers and, with our expertise in PCB manufacturing, are well-placed to support the integration of these transformers into your electronic projects, ensuring not only the assembly but also the reliability and performance of the final product. Understanding the specifics of PCB transformers can significantly influence the success of your electronic designs.

What are PCB transformers?

Transformers are electrical equipment that transforms electrical energy from one circuit to another. Using an electrical transformer has several benefits and applications:

• Circuit isolation: a transformer can isolate a device from the power grid and disconnect it from the earth. Therefore, it protects anyone who might touch loose wires or electrified surfaces. 
• Converting voltage and current without affecting overall power: you can use them in the power grid to reduce power loss. 
• Amplification of wave inputs 
• Converting the distribution wiring electricity to a suitable voltage and current for a particular device

What does an electrical transformer look like? 

An electrical transformer usually looks like a large metal box or cylinder. Pole-mounted transformers are cylindrical and often gray or green, while ground-mounted ones are rectangular and enclosed. They feature cables, bushings, cooling fins, and are marked with warning labels. Inside, they have a core and windings that transfer electrical energy.

Magnetic ferrite core transformer detail on beige printed circuit board

PCB transformers can mount on printed circuit boards as electrical components, also known as PCB-mounted transformers. Since most PCBs work below the power electronics range, most PCB transformers amplify a signal or convert electricity. 

How Do Transformers Work?

As mentioned earlier, transformers transfer electricity from one circuit to another. Now, let's see how transformers work.

A transformer has three main parts, including electronic components and magnetic components:

• The primary coil
• The core
• The secondary coil

A simple transformer model

The steps below briefly explain how a transformer alters the output voltage.

• First, when electricity passes the primary coil, it induces a magnetic flow within the metalcore. 
• Next, the magnetic flow reaches the secondary coil.
• Finally, the magnetic flow induces an electric current in the secondary coil.

In an ideal transformer, you can calculate the voltage and current of the second circuit using the following equation:

In the equation above, NP and NS represent how many rounds the coil wraps around the core. Those Numbers indicate how much you are amplifying the voltage. 

The principles stated above apply to PCB transformers, just like any other. 

PCB Transformer Composition

Inside any PCB-mounted transformer, two coils are the primary coil and the secondary coil. These coils are just coated copper wires tightly wrapped around the magnetic core. Moreover, steel or another magnetic alloy serves as the magnetic core material.

Transformer copper coil

Transformers also have terminals and an outer casing. Since you use PCB transformers on circuit boards, there are two methods to mount the transformer onto the PCB:

• Surface Mounted Transformers:
  Manufacturers design SMT/SMD transformers so you can solder them to the PCB directly. The soldering paste might loosen up if exposed to extreme heat.
• Through-hole transformers:
  As the name implies, you need to pass the leads through the PCB holes and solder the tips to the other side of the PCB. 

PCB Transformer: Main PCB-Mount Transformer Specifications

The following types of electrical equipment are the most common circuit board transformer types:

• Primary and secondary ratings:
  The rating indicates how much the primary and secondary voltage and current are. First, you have to check the output voltage. Then, check if the design current is below the transformer limits. Also, note that the more the power density, the more heat will discharge from the circuit.
• • Power rating and efficiency:
    Power rating determines the current type, AC or DC, and indicates how much power the transformer can handle. The voltage frequency is another important factor that you have to consider.
    Power efficiency tells you the direct current efficiency under a nominal load.
  • Form factor:
    A transformer can lay flat or stand vertical on the board. Vertical transformers save space, but they are prone to vibration. 
  • Mounting style:
    Some transformers are SMT type; you have to solder these transformers to the PCB surface; hence we call them surface mount technology. On the other hand, through-hole transformers require passing the leads through PCB holes and soldering them on the opposite side of the board. The latter offers better resistance to extreme heat.
  • Cooling mechanism:
    Unlike power electronic transformers, PCB-mounted transformers use much less power. Therefore, they generate less heat and don't need a particular cooling system. However, planar PCB-mounted transformers can hold a heat sink on top of the piece. 
  • Inductance:
    Simply put, inductance determines how well the transformer couples the two circuits. Inductance is also a part of DC-DC converter circuits; in other cases, power efficiency indicates the coupling performance of the transformer implicitly. 

Transformer on a PCB detail 

PCB Transformer: Types of PCB Mount Transformers

The electrical apparatus comes with different sizes of power converters and various applications.

• Audio transformers:
  You can use these tools to convert sounds and signals from about 300Hz to 20kHz.
• Autotransformers:
  This electrical equipment has only one winding which acts as both primary and secondary coils. Therefore, these efficient power convertors have different secondary voltage settings. You can connect other taps on the transformer for different conversion ratios. However, these transformers don't provide isolation since there are no separate coils.
• Balun transformers:
  This device allows balanced and unbalanced lines to be interfaced without disturbing the impedance arrangement of either stripe.
• Current sense transformers:
  These electric transformers detect and measure current in the primary winding and produce a proportional secondary current in the secondary winding. 
• Flyback transformers:
  FBT or line output transformers (LOPT) is a special transformer that creates high voltage saw-toothed signals at relatively high voltages. 

• Interface transformers: We use these electric transformers in telecoms and communication circuits with an isolated signal.
• Lighting transformers: These can generate suitable power for lightning and lumination systems. 
• Medical transformers: Medical equipment has strict regulations and tight safety guidelines. Therefore, medical transformers are safe-to-use in operating rooms for medical and surgical applications.
• Power transformers: These transformers power up the power supply of an electric device. Manufacturers, for example, utilize power transformers to power audio systems such as speakers and amplifiers.

Power supply PCB printed circuit board. 

• RF transformers: Radio frequency transformers can match impedances, isolate DC currents between circuits, and perform current or voltage step-ups or step-downs. 
• Resonant transformers: We use resonant transformers in radio circuits as bandpass filters and switching power supplies.
• Switch mode transformers or switching transformers operate under low voltage supplies. We use them in industrial and domestic applications. 

Electrical transformer

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