SiC Schottky vs Fast Recovery Diode
SiC Schottky diodes remove reverse recovery but leak more and cost more. Where the crossover sits, and why below 20 kHz a silicon FRD is usually the better buy.
OCENME Engineering · Published November 10, 2026 · 4 min read
A SiC Schottky diode has no minority-carrier reverse recovery, so it removes the turn-on loss spike in the opposing switch. A silicon fast recovery diode is cheaper and has lower forward drop at low current. The crossover in most designs sits near 20 kHz at low current and near 40 kHz at several hundred watts.
Key points
- Qrr is the cost a silicon FRD imposes on the opposing switch, and it grows 50–80% from 25 °C to 125 °C
- SiC Schottky forward drop is higher at low current, so light-load efficiency can get worse
- Reverse leakage at 175 °C is orders of magnitude above silicon — a real problem for standby power
- Below 20 kHz and under 600 V, a silicon FRD is usually the correct commercial decision
The loss that a diode does not show you
A diode datasheet reports its own forward loss. The expensive part of a silicon fast recovery diode is not its forward drop — it is the reverse recovery charge Qrr, which flows through the opposing switch at the moment that switch turns on.
Picture a boost PFC stage. The boost diode conducts, then the MOSFET turns on. For the duration of Trr, the diode still conducts reverse current, so the MOSFET sees the full output voltage while carrying both the inductor current and the recovery current. The instantaneous power spike is large, and it appears in the MOSFET’s loss budget, not the diode’s.
That is why replacing a silicon FRD with SiC can improve a design’s efficiency even though the diode’s own forward drop got worse: the saving appears somewhere else in the bill of materials.
A numerical comparison
A 400 V, 500 W PFC stage at 65 kHz. Boost diode carries an average of 1.2 A, peak 4 A.
| Item | 600 V ultra-fast FRD | 650 V SiC Schottky |
|---|---|---|
| Forward drop at 4 A, 100 °C | 1.5 V | 1.6 V |
| Diode conduction loss | 1.8 W | 1.9 W |
| Qrr at 100 °C | ~120 nC | ~15 nC (capacitive) |
| Recovery loss in MOSFET per cycle | ~48 µJ | ~6 µJ |
| Recovery loss at 65 kHz | 3.1 W | 0.4 W |
| Total attributable loss | ~4.9 W | ~2.3 W |
A 2.6 W saving on a 500 W stage is 0.5% efficiency — and because it is removed from the MOSFET, the MOSFET runs cooler, which usually allows a smaller heatsink.
At 20 kHz, the same recovery loss in the FRD case is 0.95 W instead of 3.1 W, and the SiC advantage collapses to about 1 W, which no longer justifies a 3–5× price difference.
The three regimes
| Frequency | Recommended diode | Why |
|---|---|---|
| Below 20 kHz | Silicon FRD | Recovery loss is small; cost dominates |
| 20–40 kHz | Silicon FRD or SiC, calculate | Depends on current level and cooling; both viable |
| Above 40 kHz | SiC Schottky | Recovery loss exceeds the price premium |
These are starting points. The real crossover moves with current: at 20 A and 100 kHz, SiC wins overwhelmingly; at 1 A and 30 kHz, silicon is fine.
Where SiC Schottky is the wrong answer
Standby power. SiC reverse leakage rises steeply with temperature — milliamps at 175 °C is normal. If the diode is reverse-biased across a battery or a DC link while the product is idle, that leakage is a continuous drain that can violate a standby specification.
Very low current, cost-sensitive designs. A 5 W charger does not benefit from zero recovery; it benefits from a cheap part.
Circuits that need avalanche or surge robustness. SiC Schottky diodes have lower surge tolerance per unit area than silicon PN diodes in some conditions, and their IFSM rating needs to be checked against the actual inrush, not assumed better because the technology is newer.
Designs where the diode is in series with the load. A series diode’s forward drop is a continuous loss; a SiC Schottky at 1.34 V is worse than a silicon Schottky at 0.45 V in that position.
What to ask before specifying SiC
Ask for three curves, not one number: forward voltage against current at 25 °C and 125 °C, reverse leakage against temperature, and the capacitive charge at your bus voltage. A supplier who publishes only “zero Qrr” is selling the concept rather than the device.
Then verify on your own board at your own switching frequency, because the crossover depends on loop inductance and gate drive as much as on the diode.
Our SiC Schottky page lists the 650 V / 20 A family with VF, IFSM and the 175 °C rating; the fast recovery diode page covers the silicon alternatives from 200 V to 1500 V, and the glossary explains Qrr and Trr with the conditions that make those numbers meaningful.
This article describes general manufacturing practice for machined and fabricated components. It is not a substitute for a drawing-specific engineering review — tolerances, material selection and process capability depend on the individual part.