Demystifying PCB Transformers – A Complete Guide

Demystifying PCB Transformers – A Complete Guide

Printed circuit board (PCB) transformers play a vital role in electrical systems, stepping voltages up or down as needed for power conversion.

This comprehensive guide provides an in-depth look at what PCB transformers are, how they work, their components, testing procedures, and factors guiding appropriate transformer selection for your application.

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    What is a PCB Transformer?

    A PCB transformer refers to a transformer constructed directly on a printed circuit board rather than as a separate standalone component. The transformer coils, core, and wiring are etched or mounted onto the board during PCB fabrication rather than manufactured separately.

    PCB Transformer
    PCB Transformer

    PCB transformers provide the same essential voltage conversion functionality stepping AC voltages up or down through electromagnetic induction. However, the integration directly onto a printed board allows for miniaturized power supplies, compact electronics, and efficient high density board production.

    PCB transformers can be found in consumer electronics, medical equipment, telecom devices, power converters, audio hardware, and industrial control systems. They range from small signal transformers to high power models up to 300W. Proper PCB transformers selection and integration is key to electrical system performance.

    Brief Introduction to PCB Transformers

    What Material is a PCB Transformer?

    The materials used to construct PCB transformers include:

    Copper coil windings – Formed from etched laminated copper traces on the PCB layers.

    Ferrite core – Made of ferromagnetic ceramic used to concentrate and channel magnetic flux.

    PCB substrate – Usually FR-4 glass epoxy. Electrical grade materials avoid interference.

    Solder – Used for coil terminations and mounting hardware. Lead or lead-free.

    Potting compound – Epoxy completely encased coils for protection and stability.

    Mounting hardware – Standoffs, screws and washers mount the core over the PCB coils.

    PCB transformers utilize the high trace density and reliability of printed boards to create precision coil windings not possible with hand wiring. The layered PCB fabrication process integrates all transformer elements in a compact durable package.

    How Does a Transformer Work on a Circuit Board?

    How Does a Transformer Work on a Circuit Board
    How Does a Transformer Work on a Circuit Board

    The operating principle of a transformer on a circuit board follows the same electromagnetic induction as a standalone transformer:

    ●An input AC voltage is applied to the transformer’s primary winding.

    ●This AC input current creates a fluctuating magnetic flux in the core.

    ●The changing core flux induces a varying voltage across the secondary winding.

    ●The ratio of turns between the windings steps the voltage up or down per the turns ratio.

    ●AC input is thereby converted to a different output AC voltage.

    On a PCB transformer, the copper coil traces replace wire windings to form the inductive primary and secondary circuits. The fluctuating magnetic field within the ferrite core transforms voltage just as with conventional transformers.

    Integration directly on the board allows adjusting trace widths and turns ratios to create extremely compact and customizable PCB transformers ranging from milliwatts to hundreds of watts.

    What are the Components of a PCB Transformer?

    PCB transformers contain the following key components and sub-assemblies:

    Printed Circuit Board (PCB)
    Forms the foundation on which all electrical elements and connections are mounted. Contains the precisely etched flat copper trace windings that replace standard wire coils. The PCB substrate electrically isolates and secures components.

    The ferrite core provides a controlled pathway for channeling the magnetic flux generated by the current passing through the copper trace windings. Typical core configurations are E-Cores, toroids, and E-I combinations. The core geometry and material properties heavily influence power transfer capabilities.

    Coil Windings
    The strategically shaped and routed copper traces on the PCB constitute the conductive windings of the transformer. There may be 2 to 4+ coil windings depending on the transformer topology. The trace width, length, and number of turns sets the inductance.

    Exposed solderable pads connected to each coil winding allow connections to be made between the transformer embedded on the PCB and external components or circuits. Terminations anchor the transformer electrically to the broader board.

    Mounting Hardware
    Standoffs, washers, screws, and sometimes spring clips mechanically affix the ferrite core firmly over the PCB windings beneath. This creates the closed core geometry critical for concentrating magnetic flux fields for induction.

    Potting Compound
    In high vibration environments or high voltage applications, transformers are completely encapsulated in an epoxy potting compound. This electrically insulates windings and protects against environmental contaminants. Potting increases reliability.

    Electrical Shielding
    Some precision low-level signal transformers incorporate grounded Faraday shielding cages around coils to minimize inductive interference from nearby PCB components and circuits. This allows isolation despite tight spacing.

    Thin insulation like Kapton tape, wire insulation, or plastic wraps prevent accidental shorts between tightly packed coil windings and other conductive surfaces. Insulation withstands temperature extremes.

    Larger high-power PCB transformers may incorporate heatsinks, cooling pads, airflow cutouts, or other thermal management to prevent excessive temperature rises during continuous operation at rated loads.

    What is the Difference Between PCB and Non-PCB Transformers?

    Difference Between PCB and Non-PCB Transformers
    Difference Between PCB and Non-PCB Transformers

    There are some key differences between PCB transformers and conventional standalone wired transformers:

    ●Coil Material – PCB transformers create windings from flat copper foil traces on board layers rather than using individually insulated magnet wire windings. This allows winding geometries and densities not feasible by manual winding.

    ●Automated Production – PCB transformers are manufactured on automated SMT lines capable of extremely high volume production. This compares to standalone transformers being manually wound and assembled. The consistency benefits manufacturing.

    ●Miniaturization – The printed trace construction permits much more tightly packed windings with precise dimensional control. This enables extreme miniaturization down to transformer heights as little as 3-5mm – not achievable with wound bobbins.

    ●Integrated Manufacturing – PCB transformers combine into the normal printed circuit board production process rather than requiring later discrete transformer installation. This streamlines and automates manufacturing.

    ●Customization – PCB CAD allows fully customizing winding patterns, trace widths, turns ratios, and other parameters for optimization. Hand-wound bobbins are far less configurable.

    ●Cost – At high production volumes, PCB transformer costs can be significantly lower than discrete counterparts when factoring in automated manufacturing savings. However, cost is similar at lower quantities.

    The automated printed board fabrication yields higher precision, smaller size, and full customization compared to manual winding methods. But the power transfer physics remain identical.

    How do you Test a PCB Transformer?

    PCB transformers can be tested for both manufacturing defects and design performance deviations using different methods:

    ●Design Rule CheckPCB design software verifies critical design rules like trace spacing, clearances between layers, etc. are strictly followed to avoid short circuits. This validates manufacturability.

    ●Continuity Check – A multimeter or ohmmeter checks for any open circuits or shorted loops in the winding traces indicating potential cracks or manufacturing flaws in conductors. Verifies electrical integrity.

    ●Phase Check – Apply an AC voltage to the primary coil contacts and probe the secondary to ensure the phase relationships match expectations. Confirms windings are correctly wired in PCB layers.

    ●Turns Ratio Test – Applying a fixed low voltage AC to the primary winding while probing the secondary allows validating the expected transformer turns ratio is accurately achieved, indicative of proper winding patterns.

    ●Inductance Check – An inductance meter can quantify the precise inductance both the primary and secondary windings exhibit. The measured inductances should fall within the acceptable tolerance of design targets.

    ●Magnetic Flux Test – A current probe confirms strong magnetic flux fields exist around the ferrite core when the transformer runs at nominal input voltage and load. Measures electromagnetic performance.

    ●Insulation Testing – A megohm meter verifies the insulation resistance levels between transformer windings and core meet minimum design criteria to avoid short circuit failures during operation.

    ●Hipot Testing – High potential testing stresses insulation to levels above maximum operating voltages, validating the design withstands transient spikes without arcing or dielectric breakdown.

    How do you Identify a PCB Transformer?

    How do you Identify a PCB Transformer
    How do you Identify a PCB Transformer

    Verifying the presence and specifications of a PCB transformer requires identifying key physical features and markings:

    ●Printed coils are visible on the board surface instead of wires. May be partially concealed under epoxy potting.

    ●A ferrite core is mounted over the PCB, often with an E, toroid, or EE shape.
    Standoffs secure it in place.

    ●Primary and secondary coil termination points are marked on circuit schematics with symbols for a transformer.

    ●Component reference designator like “T1” or “XFMR1” identifies the transformer on PCB silkscreens and schematics.

    ●Transformer specifications like input and output voltages, turns ratio, power rating, inductance values, insulation class, etc. provided on a component datasheet.

    ●Warning symbols indicate isolation boundaries and high voltage hazards for high voltage PCB power transformers.

    Understanding the telltale physical construction and identifying the printed coils and ferrite core verifies the presence of a PCB transformer versus a discrete wired transformer. Checking reference designators and specifications confirms transformer properties.

    How do you Choose a PCB Transformer?

    Selecting the optimal PCB transformers for a particular application requires evaluating numerous design factors and tradeoffs:

    ●Input/Output Voltages – The transformer must provide an adequate turns ratio to properly step up or down between the source input voltage and target load output voltage. Tolerances must be considered.

    ●Output Power – The continuous load current flowing through the transformer multiplied by voltage difference dictates the minimum output power rating needed to avoid magnetic saturation.

    ●Frequency – The transformer’s usable frequency range must comfortably envelope the driving circuit frequency for efficient power transfer. Higher frequencies demand more leakage inductance control.

    ●Efficiency – Higher transformer efficiency reduces wasted power dissipated as heat while maximizing usable power transfer to the load. This improves reliability while minimizing cooling needs.

    ●Size – The core and winding footprint must allow sufficient spacing and creepage distances between high and low voltage circuits for safety certifications. Footprint limits may constrain power capacity.

    ●Insulation Class – The breakdown voltage and isolation requirements dictate insulation selections to handle maximum transient voltage spikes without dielectric failure or arcing. Noise immunity also factors.

    ●Environment – Transformers must withstand temperature extremes, humidity, mechanical shock and vibration expected over the application environment range. Potting and coatings protect against contaminants.

    ●Certifications – Safety, emissions, and regulatory certifications like EN, UL, FCC required by the application may necessitate design restrictions and compliance testing. Certification costs increase with power levels.

    ●Cost – The total transformer cost balancing performance, size, features, testing requirements, and manufacturing considerations against budget constraints. Incremental improvements add expense.

    Working closely with an experienced PCB transformer manufacturer ensures making the optimal transformer choice balancing technical needs and commercial considerations.


    PCB transformers represent a specialized class of miniature transformers fabricated through printed circuit board production methods.

    By understanding their construction, functions, testing, identification, and selection criteria, electrical engineers can effectively integrate these essential devices into all manner of electronic equipment for reliable power conversion.

    The customizability and miniaturization afforded by PCB manufacturing techniques will continue fueling innovative transformer designs.

    FAQ-about PCB transformer

    A PCB transformer refers to a transformer constructed directly on a printed circuit board rather than as a separate standalone component. The transformer coils, core, and wiring are etched or mounted onto the board during PCB fabrication rather than manufactured separately.

    • Copper coil windings
    • Ferrite core
    • PCB substrate
    • Solder
    • Potting compound
    • Mounting hardware

    ●Design Rule Check

    ●Continuity Check

    ●Phase Check

    ●Turns Ratio Test

    ●Inductance Check

    ●Magnetic Flux Test

    ●Insulation Testing

    ●Hipot Testing

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