Every Schottky voltage class is a trade between forward drop and reverse leakage, and the shape of that trade is set by the junction structure and read from the datasheet curves, not from the class number alone. The selection method is to pick the lowest class that fits the reverse peak with margin—before comparing parts. This article compares the VF, IR, and blocking margin across the 45–250 V classes and maps each class to its applications.
The Voltage Classes in One View
Silicon Schottky diodes climb a ladder of standard classes—roughly 20, 30, 40, 45, 60, 100, 150, 200, and 250 V—and the useful power range stops around 250 V. Below 20 V, low-voltage Schottky classes still exist for power roles on the broader market; in this catalog, sub-45 V parts serve signal and auxiliary functions. Above 250 V the physics gets expensive enough that fast recovery or SiC takes over. Within the ladder, each step up buys more blocking margin and costs more forward drop at a given current.
The ladder is why selection starts with the class, not the part: the class determines the physics, and the part determines the execution within the class.
The ladder also has a floor in this catalog: below the 45 V rung, the catalog’s Schottky parts serve signal and auxiliary roles rather than high-current output rectification; a design below 45 V is checked against the available classes rather than assumed empty, because low-voltage power classes do exist on the market. The 45 V rung is where high-current output rectification begins, which is why the AMBRB3045CT class exists at 30 A.
VF and IR Tradeoffs at Each Class
The mechanism is the barrier and the drift structure together: higher-voltage Schottky designs typically use a higher metal-semiconductor barrier and a thicker, more lightly doped drift region, which raises VF at a given current and reshapes the leakage curve. The exact VF-versus-leakage tradeoff is read from the datasheet curves for the selected part, not assumed from the class alone. The leakage story needs the same care the physics demands: a higher barrier reduces leakage at a fixed reverse voltage, but the part is used at a higher operating voltage, so the leakage power at the working point—VR × IR at the working temperature—tends to grow with the class, and high-voltage classes are also built with structures whose series resistance raises VF further at high current. Read the datasheet curves at the working voltage and temperature rather than assuming a single trend.
The practical summary: a 45 V part conducts beautifully at 15 A with 0.64 V typical VF, while a 250 V part at 20 A sits at 0.83 V typical—both verified on the AMBR40250S datasheet and the AMBRB3045CT datasheet—and the leakage budget moves the other way with the applied voltage. The class decision is a physics trade, and the VF column is where the cost shows.
The high-current story compounds the VF cost: a high-voltage Schottky structure often carries more series resistance, so at 30–40 A the forward drop rises faster with current than a low-voltage part’s. The class cost is therefore current-dependent—small at 5 A, visible at 30 A—which is why the fit table states the test current with every VF figure.
Class-by-Class Fit Table
| Class | Typical fit | Good-Ark example (verified ratings) |
|---|---|---|
| 45 V | High-current, low-voltage output | AMBRB3045CT, 30 A, VF 0.64 V typ @ 15 A |
| 60 V | Automotive and consumer low-voltage rails | AWSS5H60 / AWSS10H60 |
| 100 V | Output rectification, BMS/BCM, lighting | AMBRP10H100, AMBRP5100, ASGC051BS, AWSS 100 V |
| 200 V | OBC DC-DC secondary, medium-voltage boards | AMBRB30200CT, 30 A, VF 0.84 V typ @ 15 A |
| 250 V | Soft-switched OBC/server stages | AMBR40250S, 40 A, VF 0.83 V typ @ 20 A |
The VF figures are stated at their test currents and are not directly comparable across rows without reading the current condition—that is exactly the point: the class cost shows up as VF at the current each application actually needs.
Reading the table the right way matters: the 45 V part at 0.64 V and the 250 V part at 0.83 V are quoted at 15 A and 20 A respectively, so the comparison is not a single curve. What the table shows is the direction—each rung up moves VF up at the current that rung serves—and the exact numbers come from each datasheet at the application’s current.
Good-Ark Class Coverage: AMBR and AWSS Series
Good-Ark’s Schottky rectifier diodes category covers the ladder from 45 V to 250 V across the AMBR, AWSS, and ASGC families: PDFN56 and TO-277B for board-level 5–10 A roles, D2PAK for 30 A board-mount, and TO-220AB for 40 A bolt-on heatsink duty. The AWSS family’s full electrical parameters are confirmed with the supplier, and the catalog row layout lets you filter by voltage class before opening datasheets.
The package mapping follows the class: PDFN56 and TO-277B serve the 5–10 A board-level rungs, D2PAK carries the 30 A board-mount rung, and TO-220AB serves the 40 A bolt-on rung. The class decision picks the physics; the package decision picks the mechanical fit, and the two are made separately.
Picking the Class Before the Part
The selection order is fixed:
- Measure the reverse peak at the node, including transients, at the hot condition.
- Apply 20–30% margin and find the lowest class that clears it—the class costs VF and leakage behavior, so the lowest fit is the efficient fit.
- Compare parts within the class on VF at the working current, leakage at the working voltage and temperature, surge, and thermal data.
- Validate the thermal result and the switching-node behavior on the bench.
The method keeps the physics decision—class—separate from the engineering decision—part—so the ladder does not get re-walked at every datasheet comparison.
The margin step deserves a concrete reading: a measured 80 V peak with transients needs a class above 80 V plus 20–30%, which lands on 100 V—the next rung. A measured 45 V peak lands on 60 V, and trying to force 45 V is a margin violation, not a cost saving.
Walkthrough: a 48 V output rail with 90 V transient peaks. The measured peak plus margin clears 100 V, so the class is set before any part is compared; within the 100 V rung, the choice is VF at the load current, leakage at the hot junction, surge, and package—the engineering trade lives inside the class, not across classes.
The same method scales from a 5 A lighting rail to a 40 A OBC output; the class decision never changes, only the numbers.
The ladder method is the same at every rung, and the datasheet columns stay the comparison sheet at each one.
The cost of over-specification is the mirror image: a 200 V part on a 60 V rail pays extra VF and leakage behavior for blocking capability it never uses, and the efficiency loss is a permanent tax on every unit. The lowest fitting class is the efficient class; the margin rule prevents the opposite mistake of under-specification.
The ladder also extends downward for signal roles, but the power catalog starts at 45 V; parts below that class serve small-signal and auxiliary functions rather than output rectification.
Engineering note. The VF figures in the fit table are datasheet-published values at their stated test currents (AMBRB3045CT 0.64 V at 15 A, AMBRB30200CT 0.84 V at 15 A, AMBR40250S 0.83 V at 20 A); the barrier mechanism describes how class affects VF and the working leakage-power picture, and the exact leakage trend for a selected part must be read from its IR–VR–TJ curves rather than assumed.
Frequently Asked Questions
Why does a higher Schottky voltage class cost more forward drop?
Higher blocking voltage needs a higher barrier, and a higher barrier needs more voltage to push current across it. The VF cost shows at the working current, which is why the lowest fitting class is the efficient choice.
Does leakage always rise with the voltage class?
Not in the simple sense—a higher barrier lowers leakage at a fixed reverse voltage—but the part is used at a higher operating voltage, so the leakage power at the working point tends to grow. Read the datasheet curves at the working voltage and temperature.
What class do I need for a 48 V output?
Measure the worst reverse peak, add 20–30% margin, and pick the lowest class that clears it—typically 100 V for a clean 48 V rail with transients. The margin rule is covered in the voltage rating guide.
When does the silicon Schottky ladder end?
Around 250 V. Above that, the physics gets expensive and fast recovery or SiC takes over; the 250 V rung itself is covered in the 250 V decision article.
How do I compare VF across classes?
Only at the same forward current and junction temperature. The class cost shows as VF at the current your application needs, not at each part’s best-looking test point.
Conclusion
The Schottky voltage ladder is a physics trade with an engineering method: measure the peak, apply the margin, take the lowest class that fits, then compare parts within it. The class decides the cost; the part decides the quality of the trade.
Walk the ladder in the Schottky rectifier diodes category on the site, and submit your reverse peak, load current, and thermal conditions to Good-Ark for a class-and-part recommendation.