What this PWM controller does in a supply
The UC3845D8 is a current-mode PWM controller that drives a single external transistor in boost, buck, buck-boost, flyback, or forward topologies. It runs from a 12 V to 28 V bias rail — common in 24 V industrial supplies — and switches the external transistor at up to 500 kHz, which shrinks the magnetics and output filter cap. The 48% maximum duty cycle caps the step-down ratio in a buck or the step-up ratio in a boost. If your design needs more than that, you are looking at a two-switch forward or a different controller family.
At 500 kHz the transformer core volume and output filter inductance drop roughly 5× compared to a 100 kHz design. That saves board space and copper cost, but the trade-off is higher switching losses in the external MOSFET and more care needed on the gate-drive layout. The 48% duty ceiling means a flyback converter running from a 24 V input can regulate down to about 12 V before the controller hits its maximum on-time. Below that output voltage you need a different topology or a transformer turns ratio adjustment.
For automotive or outdoor use the LM5150QURUMRQ1 covers -40°C to 150°C with a higher duty cycle and clock sync.
Package and footprint — 8-SOIC with tube delivery
The tube quantity suits prototype runs and small-batch production; for higher volumes the same die is available in tape-and-reel as the UC3845D8TR. Keep the supply pins decoupled with a 0.1 µF ceramic within 5 mm of each VCC pin.