48% duty ceiling — the design constraint that defines this controller
The UC3845BNST: Its 48% maximum duty cycle is the hard limit that sets the transformer turns ratio and output voltage range — you cannot push past it for a wider pulse, which means the flyback primary inductance and reflected voltage are locked in at the design stage. Switching frequency runs up to 500 kHz, letting you shrink the magnetic components for a compact supply, though the 48% duty ceiling still governs the on-time budget at any given frequency.
Through-hole DIP — rework-friendly, socket-ready
Housed in an 8-DIP (0.300", 7.62 mm) through-hole package, this controller is a bench-friendly part. The DIP body survives multiple hot-air cycles without pad lift, and the 0.100-inch pin pitch fits standard sockets or perfboard — no fine-pitch stencil needed. The supply range spans 7.6 V to 30 V on Vcc, which covers direct operation from a rectified 12 V or 24 V rail without an extra regulator. Output is a single transistor driver, positive and isolation-capable, with frequency control on the RT/CT pin.
The UC3845N (the standard DIP-8 variant without the ST-specific suffix) is a functional peer within the same family, but verify pin compatibility and any parametric differences against your specific design before substituting.