The LM2576 series of regulators from National Semiconductor are low-cost integrated circuits that provide all the active functions for a step-down (buck) switching regulator. The ICs are capable of driving a 3A load with excellent line and load regulation. The devices are available in both adjustable output and in fixed output voltage versions (3.3V, 5V, 12V and 15V).
The LM2576 requires only a minimum number of external components. A standard series of inductors optimized for use with the IC are available from several different manufacturers. Because of the high efficiency of the switching regulator, the required size of the heat sink will be small and in some cases no heat sink is required.
The regulator will work with a wide input voltage range: up to 40V for the low voltage and up to 60V for the high voltage (HV) version. Other features: external TTL shutdown capability with 50 µA standby current, cycle-by-cycle current limiting and thermal shutdown for full protection under fault conditions.
The LM2576 is available in both surface mount (TO-263 5-Lead) and TO-220 package. The pinout for the TO-220 variant (LM2576T-3.3, LM2576HVT-3.3, LM2576T-5.0, LM2576HVT-5.0, LM2576T-12, LM2576HVT-12, LM2576T-15, LM2576HVT-15, LM2576T-ADJ, LM2576HVT-ADJ) is presented on the right. For other packages, design notes and technical specifications see the LM2576 datasheet (PDF).
The schematic above is simple, easy to build and cost effective, producing 5V from a 7V-40V unregulated supply with a maximum output current of 3A. When using the LM2576HVT-5V version the input voltage can be as high as 70V.
Using the LM2576HVT-ADJ or LM2576HVS-ADJ adjustable version we can build a simple switching regulator with a 1.2-50V, 3A variable output from a 55V unregulated power supply. The maximum output current is 3A.