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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteAn ideal diode uses a power MOSFET and control circuitry to pass current with a much smaller forward voltage drop than a conventional diode, then switch off when reverse current is detected. For a robust general-purpose build, use an ideal-diode controller IC with an external N-channel MOSFET and follow that controller’s reference schematic. A single-MOSFET circuit may block reverse current without providing a full load disconnect.
What an ideal diode does
Despite the name, an ideal diode is not lossless. It emulates a diode’s one-way behavior while using a controlled MOSFET to reduce the forward drop. A conventional diode’s forward loss is largely its voltage drop multiplied by load current; an enabled MOSFET’s conduction loss is approximately current squared multiplied by its on-resistance.
For scale, Analog Devices illustrates a 1 A load through a 10 mΩ MOSFET: the calculated drop is 10 mV, compared with 600 mV typical for a regular diode in that example. These are illustrative values, not guaranteed results for every component or operating condition. Analog Devices explains the integrated ideal-diode approach.
The controller monitors voltage across the power path. When input is forward of output, it drives the MOSFET gate to turn the channel on. If reverse current is detected, it pulls the gate down so the MOSFET stops conducting. The MOSFET body diode can provide the initial forward path while the controller responds. Texas Instruments describes this operating principle in its Basics of Ideal Diodes application note.
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How to build an ideal diode circuit with a MOSFET
Use a controller IC and external N-channel MOSFET
This is the practical starting point when you need predictable reverse-current blocking. The controller handles sensing and gate drive; the external MOSFET carries load current. For example, TI’s LM74700-Q1 typical circuit senses the anode-to-cathode voltage, uses an internal charge pump to drive the gate during forward conduction, and pulls the gate down when reverse current is detected. Use the selected controller’s own schematic and pinout: pin connections, voltage limits, and control behavior are not universal.
- Define the function. Decide whether you need reverse-current blocking, reverse-polarity protection, source ORing, backup-supply switchover, or a true load disconnect. These are related but not interchangeable functions.
- Select a controller for the system. Check its input and transient voltage ratings, minimum operating voltage, reverse-voltage behavior, quiescent and shutdown current, and whether it uses linear regulation or hysteretic on/off control. Controller families can differ substantially in these capabilities; consult the data sheet and application circuit for the specific part.
- Choose the MOSFET for the available gate drive and load. Check RDS(on) at the gate voltage the controller actually supplies, current and voltage ratings, gate charge, safe operating area, package, and thermal path. A lower on-resistance can reduce conduction loss, but it does not excuse inadequate voltage, transient, or thermal ratings. Diodes Incorporated’s AN1193 MOSFET Selection Guide for Ideal Diode Controllers discusses these trade-offs.
- Wire the MOSFET in the intended direction. In the Analog Devices N-channel example, the source connects to the input so the body diode points from input toward the load. Reversing source and drain can allow the body diode to conduct from load back toward the supply while the MOSFET is off. Confirm the symbol, pinout, and controller-specific circuit before wiring.
- Build and verify the reference circuit. Follow the controller’s recommended schematic and layout guidance, then verify forward drop and reverse turn-off under the conditions that matter to your application. Do not assume one controller’s circuit can be copied unchanged to another device.
Understand the single-FET body-diode limitation
A single-FET ideal-diode stage is not necessarily a bidirectional off switch. Diodes Incorporated notes that in its single-FET controller example, if the controller does not enable the MOSFET, current can still flow in the forward direction through the body diode. That arrangement therefore does not itself provide load-switch functionality.
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If the requirement is to disconnect the load or block current in both directions while off, evaluate a back-to-back MOSFET topology and a controller designed for that arrangement. Depending on the IC and implementation, such designs can also support source selection, hot swap, eFuse functions, and voltage protection.
Choose the right implementation
| Implementation | Best fit | What to verify |
|---|---|---|
| Controller IC plus external MOSFET | General-purpose low-loss diode emulation with an appropriately selected power switch. | Controller operating and transient ranges, gate drive, MOSFET ratings and heat, reverse turn-off behavior, and whether a single FET meets the required off-state behavior. |
| Integrated ideal-diode device | A simpler power path where an integrated device’s ratings and functions suit the application. | Input range, continuous and peak current, forward loss, reverse blocking, quiescent current, protection features, and the device’s required external components. The exact values depend on the selected device. |
| Back-to-back MOSFETs with a suitable controller | Applications that need a full disconnect or broader switching and protection functions, such as some ORing or hot-swap designs. | Both-direction off-state blocking, control behavior, voltage/current limits, transient response, thermal design, and required protection features. |
TI’s ideal-diode and ORing controller overview presents controller categories and an LM74700-Q1 example. TI’s TIDA-010070 reference design provides schematic and layout resources, including an LM5050-1 ideal-diode/ORing FET controller among its listed devices. Check each design’s actual voltage, load, and protection specifications before adapting it.
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Estimate forward loss and check thermal limits
For a MOSFET operating fully on, a useful first-order estimate is Vdrop ≈ I × RDS(on) and PFET ≈ I2 × RDS(on). These estimates use the on-resistance at the relevant gate voltage and operating temperature; actual performance also depends on the device and layout.
- Analog Devices gives a calculated 50 mV drop for a 5 mΩ MOSFET at 10 A in its PowerPath controllers, ideal diodes, and prioritizers primer.
- TI’s 2021-revision application note reports 35 mV across its example MOSFET at 10 A, versus 465 mV for the Schottky diode it compares; it gives corresponding dissipation of 0.35 W and 4.65 W for those example parts.
- Diodes Incorporated’s 2025 AN1193 gives a 10 mΩ, 20 A example with a 0.2 V drop and 4 W dissipation.
These are vendor examples, not universal performance guarantees. At high current, even a modest drop creates meaningful heat. Check the selected MOSFET’s thermal resistance, PCB copper and heat path, and operating temperature. Keep sense and gate-drive routing consistent with the controller’s data sheet or reference layout.
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Account for reverse turn-off and transients
When an input supply fails or a short occurs, output capacitors can feed current back toward the failed input. How quickly the MOSFET turns off depends on more than the controller’s headline response time: comparator delay, gate-pulldown strength, MOSFET gate charge, wiring inductance, and layout all matter.
As a device-specific example, TI’s LM74700-Q1 application note specifies a maximum reverse-comparator delay of 0.75 μs and calculates a 0.77 μs turn-off example using a 5 nF gate capacitance and the stated pulldown current. Those figures describe the note’s stated conditions; they are not a timing promise for a different MOSFET, controller, or circuit.
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When to use ORing or a broader power-path design
Ideal-diode control is useful when you want to join power sources while discouraging one source from feeding another. Source ORing and backup-supply switchover still require a design matched to the sources, their voltages, expected current, transients, and desired priority. If you also need a deliberate load switch, hot-swap behavior, or protection functions, choose a controller and MOSFET topology specified for those jobs rather than treating a one-FET diode-emulation stage as a universal power switch.
There is no single universal ideal-diode schematic or bill of materials without the system’s voltage, current, and protection requirements. The controller IC and a compatible N-channel power MOSFET are the core components in the external-FET build; the right parts depend on the application.
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