AC/DC flyback controllers drive the switching timing of an external power switch in flyback-topology power supplies for small-to-medium power designs. Compared with an integrated solution, a separate controller and switch let the power device be sized independently — voltage rating, on-resistance and thermal package can be matched to the target power on their own, with more PCB layout freedom. The trade-off is more external components and design effort.
Reading the Key Parameters
- Series/type: Catalog parts fall into general-purpose multi-mode controllers, variants with an integrated external-OTP pin (allowing an external temperature-sensing device for design-adjustable over-temperature protection), smart peak-power multi-mode variants, and variants adapted to drive GaN switches. First decide MOSFET or GaN, which sets the series.
- Maximum switching frequency (fsw_max_khz): Catalog parts span 65~200kHz. Higher frequency allows smaller magnetics and higher power density, but raises switching loss and EMI difficulty; the 65kHz tier suits cost-first designs, 130~200kHz suits compact ones.
- Control modes: The catalog includes CCM/QR/DCM, CCM/DCM, QR and QR/DCM. QR (quasi-resonant) reduces switching loss and noise; multi-mode combinations cover a wider load range, while single-QR parts are typically simplified for one power tier.
- Package: SOT23-6L and SOP-7L. The former has fewer pins and a smaller footprint; the latter brings out more protection/feedback signals — the trade-off is board area versus pin count.
Three Steps to Select
- Narrow the series by target power and switch type (MOSFET/GaN).
- Fix the fsw_max_khz tier and control-mode combination by magnetics size and EMI budget.
- Check protection trip thresholds against safety/thermal requirements and confirm layout feasibility against pin count.
Common Pitfalls
- Comparing only the frequency figure while ignoring how control mode affects light-load efficiency and EMI.
- Substituting between packages without verifying pinout and protection-pin assignment.
- Mismatching the external switch to the controller's drive capability, raising switching loss beyond expectations.
To cross-compare parts by switching frequency, control mode, package and other parameters, use our online selection tool, or contact us for part-selection support.