How it works
A diode conducts mainly in one direction. Standard PN rectifiers suit line-frequency work; fast/ultrafast PN diodes control stored-charge recovery for switching. Silicon Schottky devices use a barrier junction and usually offer low forward loss at modest voltage, with a leakage tradeoff. SiC Schottky is a separate high-voltage option with little minority-carrier recovery, but capacitive charge still exists.
The diode carries current from anode A to cathode K when forward biased. Approximate conduction loss is VF × average current only when the waveform and temperature justify that simplification.
Parameters that matter
- Voltage and average current
- VRRM covers repetitive reverse voltage including overshoot. IF(AV) assumes a specified waveform and cooling condition; it is not arbitrary DC current on any footprint.
- Forward drop and leakage
- VF depends on current and temperature; IR depends strongly on reverse voltage and temperature. Include both forward and reverse heat.
- Recovery and capacitance
- For switching, compare Qrr/trr and recovery softness at matching IF, di/dt and temperature. For Schottky devices also compare junction/capacitive charge.
- Surge rating
- IFSM is a non-repetitive surge rating under a defined pulse. It is not permission for the same pulse every switching cycle.
A worked selection example
Illustrative calculation · not a product guarantee
Estimate freewheel-diode heat in a buck
Ideal asynchronous buck: 12 V input, 5 V output and 1 A load. Assume constant 0.45 V forward drop and 1 mA reverse leakage at 12 V. Ripple, switching loss and temperature dependence are not yet included; the diode values are hypothetical.
- The freewheel conduction fraction is approximately 1 − Vout/Vin = 1 − 5/12 = 58.3%.
- Forward loss is approximately VF × I × conduction fraction = 0.45 × 1 × 58.3% = 0.263 W.
- Reverse bias occupies the remaining 41.7% of the cycle. Leakage loss is approximately 12 V × 1 mA × 41.7% = 5 mW.
- Use hot VF/IR curves and actual current ripple, then add switching loss. Verify the package on the intended copper area and board.
Check forward and reverse loss together. A current label or low VF alone does not prove that a small package will stay cool.
Where it fits
Suitable starting points
- AC input bridges; secondary rectification; freewheel paths; reverse-polarity and diode OR-ing where loss is acceptable.
Where to take extra care
- Do not use a standard line rectifier in a high-frequency recovery-critical path. A TVS is not a normal power rectifier; a low-VF Schottky is not always best at high temperature.
Series directions to investigate
Investigate Yangjie’s separately listed rectifier, fast-recovery and Schottky lines; JSMC lists SBD, trench SBD, SiC SBD and FRD directions. SMA/SMB/SMC, low-profile SMD, TO packages and bridge packages require distinct thermal/footprint checks. A bare-die sheet is not a packaged-part approval.
What Chinese suppliers can offer
Where the opportunity lies
The concrete domestic strength is breadth across rectification processes and package formats, allowing a supplier search to follow the circuit’s loss and assembly needs. Compare total heat and surge capability before consolidating suppliers; neither a familiar SSxx marking nor an environmental declaration proves equivalent die or reliability.
What still needs evidence
Confirm the exact manufacturing source, current datasheet, sample results and commercial terms before placing an order. Series availability does not establish qualification for your application.
Questions for the supplier
- 01
Maximum hot VF/IR, derating curves and the exact thermal mounting condition.
- 02
Recovery/capacitance data for switching duty and surge pulse definition for startup.
- 03
Packaged ordering code, die/process revision, traceable lot and matching reliability report.
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. Official product categories
- 2. TSB94S150SS-255A chip sheet
- 3. Superjunction MOSFET selector
- 4. Schottky barrier diodes
- 5. AN4021: Calculation of reverse losses in a power diode
- 6. Basic Calculation of a Buck Converter Power Stage, SLVA477B
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.