Power Path and Ideal Diode Selector
Compare Schottky diodes, discrete P-MOSFET stages, and ideal-diode controllers for low-drop power paths, OR-ing, and reverse-current protection.
Quick start examples
Presets load representative numbers. Final selection still depends on the exact part, fault profile, and layout.
Inputs
How to choose
Operating point
Compare the three options at one representative operating point. Use continuous or worst-case steady current, not only short startup pulses.
Examples: 50 mV for low-voltage battery rails, 100 to 200 mV for less sensitive higher-voltage paths.
Thermal context
The thermal model here is only a board-level comparison aid. It does not replace a package datasheet or real thermal measurements.
Representative board-level thermal path will appear here.
What this tool is good for
- Good at: first-pass comparison of drop, loss, and thermal direction.
- Not enough for: hot-plug surge sizing, fault SOA, TVS selection, or final package temperature sign-off.
- Best workflow: choose an architecture here, then validate with a real part datasheet and your exact topology.
Recommended approach
Waiting for inputs
Enter a realistic operating point to compare voltage drop, loss, and board-level thermal stress.
This summary is intentionally conservative. If two sources can be alive at the same time, controller-based OR-ing usually deserves extra weight.
Schottky diode
Simplest path
Lowest BOM count, but the drop is usually measured in hundreds of millivolts.
Estimated voltage drop
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Discrete P-MOSFET stage
Balanced option
Much lower drop than a diode, but startup and reverse-current behavior depend on the exact topology.
Estimated voltage drop
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Ideal-diode controller
Most controlled option
Lowest drop and better reverse-current handling, usually at the cost of an IC and a more deliberate implementation.
Estimated voltage drop
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Model assumptions
- Schottky: representative forward drop in the rough 0.3 V to 0.6 V range, depending on current.
- Discrete P-MOSFET stage: representative conduction path around a few tens of mOhm.
- Ideal-diode stage: representative controller plus MOSFET path with drop in the tens-of-millivolts range and small controller IQ.
- Thermal model: first-order board estimate only. Package thermal impedance and airflow can dominate the real result.
Architecture notes
The right answer is often driven less by raw drop than by fault behavior, source priority, and how much validation time you want to spend.
When a Schottky still makes sense
- Current is low enough that heat stays modest.
- The system can tolerate a few hundred millivolts of drop.
- You want the simplest possible path with predictable behavior.
When a discrete MOSFET stage fits
- You need much lower loss than a diode, but BOM cost still matters.
- You can validate the exact startup and reverse-current behavior of the topology.
- The application is not relying on controller-managed OR-ing edge cases.
When an ideal-diode controller earns its keep
- Voltage headroom is tight or current is high enough that drop quickly becomes heat.
- Two sources can be live at once and clean handoff matters.
- You want faster, more explicit reverse-current blocking behavior.
Practical caution on P-MOSFET stages
A common reverse-battery or low-loss input stage uses the MOSFET body diode only during startup, then the channel turns fully on and the drop collapses to I x Rds(on). That is useful, but it is not the same thing as a fully managed OR-ing controller.
Why current changes the tradeoff so fast
Diode loss scales roughly with I x Vf, while MOSFET conduction loss scales with I squared x Rds(on). At low current, the simplest architecture may be fine. At higher current, even a modest Schottky drop can dominate both efficiency and thermal budget.
Why ideal-diode controllers are different
Controller-based ideal diodes are built specifically to replace lossy discrete diodes in power-path and OR-ing applications. They drive a MOSFET so the forward drop lands in the tens-of-millivolts range instead of the hundreds-of-millivolts range typical of a Schottky path.
They also watch the path direction and turn off quickly when reverse current starts to develop, which is why they tend to be safer in redundant-source and hot-plug designs.
Where back-to-back MOSFETs enter the picture
A single MOSFET still contains a body diode, so it does not automatically block current in both directions whenever the path is off. Back-to-back MOSFETs are used when off-state bidirectional blocking or controlled isolation is required.
That is common in robust input protection, hot-swap control, or designs that must survive faulted or back-driven outputs without ambiguous current paths.
How to interpret the thermal estimate
The thermal number here is a board-level comparison aid using an estimated ambient path derived from copper area. It is useful to rank architectures quickly, but it is not a substitute for package theta JA, SOA limits, or lab measurements.
If your estimate is already uncomfortable here, assume the real design needs a more careful thermal pass before release.
FAQ
Why not always use a Schottky diode?
A Schottky diode is simple and robust, but its forward drop is usually a few hundred millivolts. That wastes headroom and turns directly into heat at higher current.
When is a discrete P-MOSFET stage enough?
A discrete P-MOSFET stage can be a good low-loss option for reverse-polarity protection or a simple power path. For strict OR-ing behavior, hot-plug robustness, or guaranteed reverse-current blocking, validate the exact topology carefully or step up to a controller-based ideal diode solution.
Why do back-to-back MOSFETs appear in many protection designs?
Back-to-back MOSFETs are used when a design must block current in both directions while the path is off or faulted. A single MOSFET still has a body diode, so topology matters.