120 V, 40 A Schottky in a common-cathode TO-220
Each diode delivers 20 A average (Io) with a forward voltage of 1 V at the 40 A peak rating. The fast recovery characteristic (≤500 ns, >200 mA) suits it for high-frequency switching supplies and output rectification stages where Schottky's low Vf and fast turn-off reduce losses. Packaged in a TO-220-3 through-hole case (TO-220AB narrow leads), the common-cathode pair shares the center tab, simplifying layout for center-tapped secondary rectifiers or OR-ing diodes in redundant power feeds. The junction is rated to 175°C max, giving headroom for thermally demanding environments like industrial power supplies or telecom rectifiers.
ST lists the STPS40120CTN as Obsolete. No last-time-buy window remains open from the factory. New production designs should migrate to a current Schottky from ST's portfolio or a pin-compatible alternative. For existing BOM lines, stock is available through independent distribution; each lot is date-code verified and quoted per RFQ.
Forward voltage and conduction loss
At 40 A forward current the STPS40120CTN drops 1 V. That 40 W peak dissipation per diode pair drives the thermal design — the TO-220 tab must be heatsinked, and the 175°C junction limit sets the allowable case temperature. For a 20 A average load per diode, the Vf will be lower (the 1 V spec is at the 40 A peak), but the thermal margin still needs checking against the heatsink's thermal resistance.
Reverse leakage at 120 V
Reverse leakage is 25 µA at 120 V, typical for a 120 V Schottky. That leakage doubles with temperature, so at high junction temperatures the standing loss in off-state can become significant in low-load or standby conditions. For always-on OR-ing applications, verify the leakage budget at the operating temperature.