The most common questions about selecting and using switching power supplies, EMI power filters and servo transformers, answered by the Shanghai Fengchuang engineering team.
Common causes: (1) input voltage below the rated range; (2) load power exceeds the rating, pulling the output down; (3) voltage drop on long or thin cables — the terminal reads fine but the load end is low; (4) the output adjustment potentiometer was turned; (5) aged electrolytic capacitors reducing load capability. Check input voltage first, then verify load power, then inspect wiring gauge and the potentiometer.
Insertion loss measures how strongly the filter attenuates interference, in dB — higher means stronger attenuation. Datasheets show separate common-mode (CM) and differential-mode (DM) curves, measured in a 50Ω/50Ω system. Match the curve to the frequency band and mode where your equipment actually fails, and keep margin because real-world impedance differs from lab conditions.
Choose 1.2 to 1.5 times the maximum load current, then apply the temperature derating curve if the ambient is hot or cabinet cooling is poor. Undersized filters overheat; oversized ones waste space and cost and may have weaker low-frequency insertion loss.
Single-phase filters are used on 220V single-phase circuits — typical points are switching power supply inlets, single-phase equipment and instruments. Three-phase filters are used on 380V three-phase circuits — typically VFD inputs, servo drive main circuits and high-power equipment. Check phase-current balance when selecting for three-phase loads. FONYUN FYL single-phase models cover small currents up to tens of amps; FYL-3N three-phase models cover 10A to over 100A.
Standard switching power supplies should not be paralleled directly: small output-voltage differences make one unit carry the whole load while the other idles, causing uneven sharing or damage. Only models that explicitly support parallel current-sharing may be paralleled — check the datasheet. For more power, prefer split-zone feeding or a single larger unit.
(1) Use a standard 35mm DIN rail and confirm the unit is clipped and locked; (2) these supplies cool by natural convection — leave clearance above and below and avoid mounting next to strong heat sources such as VFDs; (3) derate above 40°C ambient per the datasheet curve; (4) tighten all input/output terminals and avoid exposed strands; (5) in high-vibration environments add end brackets to the rail.
Every product page has its datasheet attached — open the product detail page and download directly. You can also batch-download Chinese and English versions from the Support / Downloads section. For paper copies or the latest revision, contact our sales team.
Typical protections include short-circuit protection (SCP), overcurrent protection (OCP) and overvoltage protection (OVP); some series add over-temperature protection (OTP) or input under-voltage protection. After a protection event most models recover by power cycle or automatically — the exact behavior is specified in each model's datasheet.