A workhorse DC-DC controller for legacy and repair BOMs
The ON Semiconductor MC34063AD is a monolithic switching regulator controller that handles step-up (boost), step-down (buck), and inverting topologies from a single 8-pin SOIC package. It integrates a 1.5 A rated switch transistor, a 100 kHz oscillator, and a temperature-compensated voltage reference — enough to build a non-isolated supply rail without an external controller IC. The adjustable output is set by two external resistors from a 1.25 V reference, and the output can be configured as positive or negative relative to the input common. The wide 3 V to 40 V input range covers 5 V, 12 V, 24 V, and 48 V bus rails common in industrial control, telecom, and automotive aftermarket equipment.
What the 1.5 A switch rating and 100 kHz oscillator mean for your design
The 1.5 A switch current is the peak current the internal transistor can handle — not the continuous output current. In a typical buck from 24 V to 5 V, expect around 500 mA to 750 mA output before the switch saturates or the thermal limit in the SOIC-8 package becomes the constraint. The 100 kHz fixed oscillator sets the inductor value; for a 5 V output at 500 mA you are looking at a 100 µH to 220 µH inductor, which keeps the board footprint manageable but limits the transient response compared to modern 500 kHz+ parts. No synchronous rectifier is built in — the freewheeling diode is external. That means efficiency tops out around 70-80% depending on the diode forward drop and the duty cycle.
Sourcing an obsolete part — what to expect
ON Semiconductor no longer manufactures this specific variant in the SOIC-8 package. For new designs, the MC34063A family is broadly second-sourced by multiple manufacturers (Texas Instruments, STMicroelectronics, Microchip) in PDIP-8 and SOIC-8 packages, though pin compatibility varies by vendor. If you are filling a repair or retrofit BOM, the MC34063AD is the exact SOIC-8 variant to match the original board layout.