Ideal Diode
An ideal-diode controller drives the gate of an external P-MOSFET or back-to-back N-MOSFETs to replicate a diode's one-way behaviour. It monitors the drain-source voltage and turns the MOSFET on only when forward current would flow, turning it off instantly when reverse current is detected.
A fast comparator monitors Vds of the MOSFET. When Vds is negative (forward condition), the controller turns the FET fully on to minimise drop. When Vds reaches zero or goes positive (reverse condition), it turns the FET off in nanoseconds, blocking reverse current far faster than a diode's junction would.
In plain terms
A Schottky diode burns 0.3 V as heat. An ideal-diode controller watches the voltage across a MOSFET and turns it on when current wants to flow forward, off when it wants to go backward — mimicking the diode with a 10 mΩ switch instead of a junction.
Why designers use it
- OR two power rails (adapter + battery) with millivolt drop instead of 0.3–0.7 V.
- Replace Schottky diodes in battery backup paths and save tens of milliwatts.
- Protect against reverse-current flow in solar panels and supercapacitor banks.
Best for
- Power OR-ing
- Battery/adapter mux
- Low-loss backup
Key specifications
- Operating voltage: 1.5 V – 80 V
- Forward drop: 20 – 50 mV (Vs 0.4 V Schottky)
- Reverse leakage: <10 µA
- Switching speed: 1 µs – 50 µs
- Reverse-current detection: 1 mA – 100 mA
When not to use it
- When the two rails can have large voltage differentials and MOSFET Vgs requirements become complex.
- When simplicity matters more than efficiency — a Schottky needs no IC and no passive component.
Common mistakes
- Using an N-MOSFET in a P-MOSFET topology without a charge-pump, leaving the gate un-driven above the source.
- Selecting a MOSFET with gate capacitance too large for the controller's gate-drive current, causing slow switching and linear-mode heating.
Where you will find it
- In an illustrative power path, a controller and suitable MOSFET can reduce forward loss compared with a diode while managing reverse current according to the selected device's behavior.
- A battery-backup design must check switchover behavior, output hold-up, load transients and fault conditions. No universal transition time or medical-safety guarantee follows from the component name.
A short history
Ideal-diode controllers drive a low-on-resistance power MOSFET to replace a conventional Schottky diode in power-OR (redundant supply) and reverse-polarity protection circuits, reducing forward voltage drop from ~0.4 V to a few millivolts and dramatically cutting power dissipation. Linear Technology (now part of Analog Devices) introduced the LTC4412 'PowerPath' controller around 2000, a pioneering ideal-diode controller IC. These devices monitor the drain-source voltage of the MOSFET and adjust the gate voltage in real time to hold VDS near zero during forward conduction while blocking reverse current with near-zero standby loss. They are now standard in high-efficiency battery-powered and server power systems.
Good to know
- An ideal-diode controller turns on an external N-channel MOSFET whenever forward current flows, and shuts it off on reverse current — emulating a Schottky with milli-volt drop instead of half a volt.
- Two ideal diodes form an OR-ing power supply: drive a load from whichever rail is higher, with no diode loss. The classic redundant-supply trick of telecom gear.
- Battery-powered designs use ideal diodes to merge USB and battery rails; saving 0.5 W per 1 A means 30 minutes more runtime on a phone.