The UC3845BD1013TR is a current-mode PWM controller from STMicroelectronics designed for boost and flyback converter topologies. It drives a single external power transistor and includes frequency control for oscillator trimming. The 7.6V to 30V supply range lets it run directly off a 12V or 24V industrial bus without a pre-regulator, and the -40°C to 150°C junction temperature covers both outdoor telecom cabinets and under-hood automotive auxiliary supplies.
Switching frequency and duty-cycle limits
Switching frequency is programmable up to 500 kHz via an external RC timing network. Higher frequencies reduce transformer and capacitor size but increase switching losses — a typical flyback for a 10–20 W auxiliary rail runs at 100–200 kHz to balance magnetics volume against thermal budget. Maximum duty cycle is 48%, which limits the step-up ratio in boost converters and the reflected voltage in flyback designs. The 48% cap keeps transformer reset margin in single-ended topologies without requiring a separate reset winding.
8-SOIC (0.154-inch, 3.90 mm width) surface-mount package. The 1.27 mm pin pitch is layout-friendly for two-layer boards, and the body width matches the standard SOIC-8 land pattern used across the industry. The 150°C TJ max is typical for junction-rated controllers — the ambient ceiling depends on the thermal resistance of the board.