schottky diode

[baldrick]

I decided to make a hot swap plate up using Two 12 v batteries. Using Two Vishay vs-90sq040
Schottky diodes Ord together.

The circuit works fine with the two batteries connected. But the problem is with one battery disconnected, I can measure full battery volts across the other diode which is meant to be blocking, I thought that diodes should block volts going across the diode in the reverse direction?

When I put a low value resistor across the battery adaptor + and - terminals, the volts on that diode dissapears.

The reverse leakage for this diode is 1.75ma.

Any ideas?

 

[Diver300]

Welcome to the forum.

The reverse leakage current of the diode is keeping the voltage up at the battery voltage. It doesn't matter. As you found out, if there is a current path to ground, the voltage falls, but the loas is still supplied by the other battery and the other diode. The diode is still stopping a low voltage on one battery from shorting out the supply.

 

[vlad777]

SiC (silicon carbide) Schottky diodes have low leakage currents.

https://export.farnell.com/rohm/scs110ag/diode-sic-recti-600v-10a-to220ac/dp/1907963

 

[baldrick]

Hi,

Thanks for coming back promptly.

I failed to explain that there is no load connected at this point, I was purely messing about with Two batteries to see how the hot swap, and how the diodes would perform in the circuit. The highest voltage being used out of the Two batteries.

The reverse leakage you say is holding the battery voltage across the blocking diode.

I can't understand how that small leakage current would still allow full battery voltage which is 16v in this case, probably a few volts is what I would expect to see.

Can you shed a further explanation to this?


I know that the diode are not faulty, as I have tried several from different batches.

There don't seem to be any online info or books which actually explain this principle.

 

[vlad777]

Your meter has 10MOhms input resistance. 12V/10MOhm is much smaller than leakage current.
So the diode allows all of that smaller current to pass and the meter reads 12V.

(It's like the leakage current is too big to be a bottleneck in this case.)