What this Schottky pair does in the circuit
The STPS4045CP is a dual Schottky rectifier from STMicroelectronics, configured as a common-cathode pair in a through-hole TO-218-3 (also known as SOT-93) package. The forward voltage drop is specified at 760 mV at 20 A, which keeps conduction losses manageable in high-current rectification stages. The fast recovery characteristic (≤500 ns, >200 mA) suits switching power supplies and freewheeling diode applications where reverse-recovery charge matters. With a maximum junction temperature of 175°C, it can handle the thermal stress of industrial power converters and automotive-grade alternator or motor-drive circuits.
45 V reverse voltage — what it buys you
The 45 V Vr(max) gives comfortable headroom on a nominal 24 V or 36 V DC bus, including transients typical in industrial power supplies and battery chargers. If your rail is 48 V or higher, you need a higher-voltage Schottky — the STPS4045CP is not the part for that.
STMicroelectronics lists the STPS4045CP as obsolete. The part must be sourced through independent distribution or surplus channels.
Mounting and thermal notes
The through-hole TO-218-3 package with a metal tab is meant for bolting to a heatsink. The 175°C junction rating only holds with proper thermal management — the tab carries the heat, so a thermal pad or grease and a mechanical fix are assumed in the design. MSL is not stated, but a through-hole part of this era typically ships dry; still, if the tube has been open, a short bake before reflow is cheap insurance against moisture-related damage during soldering.