Automotive Qualified Redundant Power Supply with Ideal Diodes

The electrons are taking over my desk again. This time I am playing with an ideal diode, the LT8672. This device detects the forward voltage drop across the body diode of an NFET and when this is greater than a few hundred milliVolts, it turns on the FET, thus creating a forward path with low loss.

It then measures the voltage across the FET and if this voltage goes negative, it turns off the FET and the body diode stops the reverse current.

So you have low conduction losses in the forward direction and the blocking of the body diode in the reverse direction... a diode that is 'ideal'

Very useful when you cannot afford the 0.6V drop of the diode (where input voltage is precious or load current creates too much heat dissipation).

Putting my psycho hat on, I thought I would test it.

I shorted together the outputs of two LT8672's and fed separate 12V supplies into each input. I connected up a 30A load. The 12V inputs were supplied by two car batteries I purchased from 'Mickey One-Punch' at the local scrapyard and can source up to 300A each. One 12V input measured at 12.2V and the other measured at 12.5V. I connected one permanently to one input and connected/disconnected the other input.

The output waveform is shown below - perfect switching between one input and the other. If one input gets disconnected, the other input seamlessly takes over.

The FETs on the evaluation kit are rated at 100A, so this circuit can provide a very high current, redundant power supply solution that is automotive qualified and will work up to 42V.