The STPS40SM120CTN is a dual Schottky rectifier from STMicroelectronics, configured as a common-cathode pair in a single TO-220-3 package. The fast-recovery characteristic (≤ 500 ns at > 200 mA) suits it for high-frequency switching supplies and output rectification where Schottky's low Vf and fast commutation reduce losses. The common-cathode layout pairs naturally with center-tapped transformer secondaries or as a dual OR-ing diode in redundant power feeds.
Obsolete — no official successor on record
STMicroelectronics lists the STPS40SM120CTN as Obsolete. No official replacement order code appears in the lifecycle record. A buyer holding a production requirement should qualify a pin-compatible Schottky pair from the same voltage/current class for dual-sourcing resilience.
Housed in a TO-220-3 through-hole package, the part is through-hole mounted for heatsink attachment. The metal tab is the common cathode — insulate or ground it per the board's thermal and electrical plan. Junction temperature maxes at 150 °C, so the heatsink must keep the case temperature within the derating curve at 20 A continuous per diode.
Leakage and reverse recovery
Reverse leakage is specified at 275 µA at the full 120 V rating — a typical number for a 120 V Schottky at elevated temperature. The ≤ 500 ns recovery time (above 200 mA) is fast enough for most 50–100 kHz SMPS designs, though modern SiC or higher-voltage Schottky parts may offer lower Qrr for higher-frequency stages.