Fixed 3.3V buck at 3A — the TO-220-5 workhorse
The LM2576T-3.3/LB03 is a SIMPLE SWITCHER step-down regulator from Texas Instruments, delivering a fixed 3.3V output at up to 3A from a 4V to 40V input rail. It uses a 52 kHz buck topology with no synchronous rectifier, so the external Schottky diode handles the catch current.
52 kHz switching — inductor size trade-off
The 52 kHz switching frequency is low by modern standards, which means the external inductor and output capacitor will be physically larger than what a 200 kHz+ switcher would need. For a 3A design, expect a 100 µH to 330 µH inductor and a 330 µF to 1000 µF electrolytic on the output. The trade-off is lower switching losses and better efficiency at moderate loads, but the board area penalty is real.
For existing BOM lines, the only supply channel is independent distribution — surplus, new-old-stock, or broker inventory. No official successor is listed on the record, but the LM2576 series includes other fixed-voltage variants that share the same pinout and footprint.