MBR140SFT1G

The MBR140SFT1G from onsemi is a 40V 1A Schottky barrier rectifier diode in a compact SMA (DO-214AC) surface-mount package. As a Schottky diode, it uses a metal-semiconductor junction rather than a P-N junction, resulting in a significantly lower forward voltage drop (0.5V typical at 1A) compared to silicon P-N diodes (typically 0.7-1.0V). This lower forward voltage directly translates to reduced conduction losses in power supply applications, improving overall converter efficiency. Schottky diodes are majority-carrier devices, meaning they have essentially zero reverse recovery time (no stored minority charge to remove), making them ideal for high-frequency switching applications such as buck converter free-wheeling diodes, boost converter output diodes, and reverse polarity protection circuits. The 40V reverse voltage rating provides adequate margin for 12V and 24V power supply output stages. The guard ring structure around the Schottky junction provides ruggedness against voltage transients and enhanced ESD protection. The MBR140SFT1G is AEC-Q101 qualified, suitable for automotive applications. The SMA package provides a good balance between current handling capability (1A) and board space (5.2 x 2.6mm footprint). The T1G suffix indicates onsemi’s lead-free, RoHS-compliant termination finish with MSL 1 (unlimited floor life).

The MBR140SFT1G operates as a Schottky barrier rectifier using a metal-semiconductor junction. Key operating principles include: (1) Schottky Junction – a rectifying junction is formed between a metal (typically a refractory metal such as molybdenum or tungsten silicide) and lightly-doped N-type silicon; unlike a P-N junction where both holes and electrons participate, the Schottky junction is a majority-carrier device where only electrons flow from the semiconductor to the metal under forward bias; (2) Low Forward Voltage – the metal-semiconductor junction has a lower barrier height (approximately 0.4-0.5V for typical power Schottky diodes) compared to a P-N junction barrier (0.6-0.7V); this results in a lower forward voltage drop at a given current density, directly reducing conduction power loss (P = VF x IF); (3) Zero Reverse Recovery – since the Schottky junction is a majority-carrier device, there is no stored minority charge to remove during the reverse recovery transition; the diode turns off almost instantly when the voltage reverses, limited only by junction capacitance charging; this eliminates the reverse recovery loss (PRR = QRR x VR x f) that plagues P-N diodes in high-frequency switching applications; (4) Guard Ring – a P-type guard ring surrounds the Schottky contact, providing a P-N junction that acts as a voltage clamp during transient overvoltage events, protecting the Schottky junction from damage; (5) Reverse Leakage – the tradeoff for low VF is higher reverse leakage current compared to P-N diodes; at 25C and rated reverse voltage, leakage is typically 0.5mA maximum, increasing exponentially with temperature (approximately doubling every 10C).

• DC-DC buck free-wheeling: replaces P-N diode in buck converter output, reducing conduction loss by 30-50%
• Reverse polarity protection: series diode at power input; 0.5V VF reduces voltage loss vs 0.7V P-N diode
• Solar panel blocking: prevents battery discharge through solar panel at night with low voltage drop
• Battery OR-ing: two batteries diode-ORed to load with minimum voltage drop