The LM2577T-ADJ/LB03 is a SIMPLE SWITCHER regulator from Texas Instruments, configurable as a step-up (boost), flyback, or forward converter. The internal 3 A switch and 52 kHz switching frequency target designs where transformer size and EMI filter cost are secondary to simplicity — the part integrates the compensation and requires only the inductor/transformer, diode, and output capacitor to complete a supply. Output is adjustable from 1.23 V up to 60 V (switch voltage limit), positive polarity only. The 3.5 V minimum input allows operation from a 2-cell Li-Ion stack or a 5 V rail; the 40 V maximum input covers most industrial and automotive bus voltages with margin.
NRND — sourcing through distribution
No official successor is recorded on the evidence. The LM2577 family has no pin-compatible drop-in; a new-design evaluation should consider a higher-frequency synchronous alternative such as the LMR33630 (2.1 MHz, 3 A, buck only) if the topology permits.
The TO-220-5 package with formed leads (through-hole) simplifies prototyping and rework. The 52 kHz switching frequency is low enough that layout parasitics are forgiving, but the transformer core size for a flyback design will be larger than a modern 500 kHz+ controller. Plan the magnetics around the minimum input voltage and the 3 A switch current limit.