Mini PCB current transformers are tiny magnetic components that measure AC current directly on the printed circuit board – no isolation amplifier, no shunt resistor heat, no galvanic isolation worries. They are the standard solution for metering, monitoring, and protection circuits in compact electronic products. This guide explains how mini PCB current transformers work, their key specifications, and how to select one for your design.
What Is a Mini PCB Current Transformer?
A mini PCB current transformer is a small, PCB-mountable current transformer that senses alternating current flowing through a primary conductor. The primary is typically a single turn – the conductor passes through the core window – while the secondary winding is wound on a tiny toroidal core and terminated to PCB pads. The secondary delivers a current proportional to the primary current, which the measurement circuit converts to a voltage across a burden resistor. Mini PCB current transformers are available in through-hole and SMD versions for board densities from a few amps to hundreds of amps.
How Mini PCB Current Transformers Work
The AC current in the primary conductor creates an alternating magnetic flux in the toroidal core. This flux induces a current in the secondary winding that opposes the primary flux, so the secondary current is the primary current divided by the turns ratio – the transformer operates essentially as a current source. The measurement circuit loads the secondary with a burden resistor, producing a voltage proportional to the primary current. Because the primary and secondary are galvanically isolated, the transformer also provides isolation between the power circuit and the measurement electronics, typically rated for 1 kV to 5 kV.
Key Specifications of Mini PCB Current Transformers
Rated primary current: The nominal current the transformer measures, for example 5 A, 10 A, 30 A, or 100 A.
Transformation ratio: The primary-to-secondary turns ratio, such as 1000:1 or 2000:1, which sets the secondary current for a given primary current.
Accuracy class: The measurement error at rated current – classes such as 0.5, 1, or 3 for metering, and protection classes for relay use.
Burden: The load (resistance and VA) the secondary can drive while maintaining accuracy; the burden resistor value scales the output voltage.
Frequency range: The operating band, typically 50/60 Hz, or wideband versions for 20 Hz-100 kHz measurement.
Isolation voltage: The primary-to-secondary withstand voltage, important for safety isolation in mains-connected designs.
Size and footprint: Core window for the primary conductor and PCB footprint; SMD versions for high-density boards.
How to Choose a Mini PCB Current Transformer
Define the measurement range and accuracy first: the maximum primary current, the required accuracy class at the operating point, and the output voltage you want across the burden. Choose the turns ratio and burden that give the target sensitivity (mV per amp) while staying within the transformer’s accuracy envelope and the ADC input range. Check the frequency range matches your signal – 50/60 Hz for mains monitoring, wideband for power quality or current sensing in switching circuits. Confirm the isolation voltage for your safety class, and select the footprint (through-hole vs SMD, core window size) for your PCB layout. Shaanxi SiRui Technology Co., Ltd manufactures mini PCB current transformers – through-hole and SMD, standard and custom ratios – under ISO 9001:2015 quality management with RoHS and REACH compliant materials.
Applications of Mini PCB Current Transformers
Smart meters and energy monitoring, power supplies and adapters, air conditioners and appliances, EV chargers and wallboxes, lighting drivers, UPS and inverters, industrial drives and panel meters, battery chargers, welding machines, and IoT power sensors.
FAQ
How do I choose the burden resistor?
Select the burden so the output voltage matches your ADC range at the maximum measured current, while keeping the secondary within the transformer’s rated burden – typically 1-10 ohm for mini current transformers.
Can a PCB current transformer measure DC?
No – a conventional current transformer only measures AC. For DC or mixed AC/DC current, use a Hall effect sensor or fluxgate solution.
What is the accuracy of a mini PCB current transformer?
Typical metering-grade parts achieve 0.5% to 1% accuracy at rated current and frequency; protection-grade parts sacrifice accuracy for saturation performance.
Do you supply custom mini PCB current transformers?
Yes. Shaanxi SiRui Technology Co., Ltd supplies custom ratios, burdens, footprints, and isolation ratings from samples to volume production, with full test documentation.
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