Low voltage drop high current unidirectional diode/circuit

Experts!

Need help in continuation of a circuit I was working on, for which I had great inputs from the community. This was the original post:

https://www.edaboard.com/showthread.php?380027-MOSFET-switchover-for-E-Bike-controller

Referring to the above, I had managed to get a LFP battery with inbuilt BMS. That helped me create a MOSFET based switch alright (since charge and discharge connections are separate unlike the earlier circuit), but there is still one nagging issue I cannot find a solution/suitable component for.

I intend to use a diode to ensure that current is flowing only in one direction - from the battery to the controller and not the other direction. But 0.7V - 1V drop across the voltage takes away a lot of usage capacity out of my battery. The battery is a 48V (nominal)-52V(maximum) 15S4P LFP battery. If I deduct even 0.7V, it is considerable amount of energy wasted across the diode.

Is there a diode/schottky diode/any other active circuit that would have very low voltage drop/current consumption that would allow flow of current only in one direction? Might be I could use a high current MOS without a body diode which I could turn on in one direction along with the main MOS, and leave it OFF and blocking in the reverse direction?

Thanks a ton!
-Deepak

Hi,

It's still 8A - 10A? 5.6W to 7W, or 8W to 10W...

Never used MOSFETs without a body diode so couldn't say. Back-to-back MOSFETs is another option, just double the RDSon, if chosen wisely with very low RDSon and checking the curves in the datasheets, should/could be low enough. Schottky diodes are supposed to have "high" leakage, but it might bring diode PD down to ~4W max, depends again on checking device datasheet graphs for reliable assessment.

Hi,

0.7V from 48V is just 1.4%.
Because the current and time is the same: you waste just 1.4% of the energy.. or you have 98.6% efficiency with this. Not that bad.

Is there a diode/schottky diode

Click to expand...

--> go to a diode manufacturer ir a diode distributor web site and use the interactive selection tool.

any other active circuit

Click to expand...

--> look for "ideal diode" circuits or ICs.

Klaus

@KlausST - forgot to mention that the operating range is just about 42-52V. So 0.7V is also still 7%. That's a lot of juice wasted in an e-bike situation, hence trying to find the most optimised solution. Any diode seems to be having
@d123 - this time its in the discharge path, so higher current (23A-25A @ 48V). I actually thought of back-to-back (N-channel and P-channel combo) MOSFETs as you suggested, and drew a crude diagram as well. I think that might work. Even if the RdsON adds up, should still be better than . I'll build it and see if that works well. Will keep posted.

Hi,

Your efficiency calculation is wrong. You have to calculate with the average (or the nominal) voltage, not with the difference.
It's not 7% loss.

Don't expect a noticable extension of battery lifetime.

Klaus

I would think that an e-bike would -love- current flowing
from controller to battery - at least, during regenerative
braking. Why the concern over reverse current flow?

@KlausST - I'll try with the diode anyway as a start to simplify things and assess the impact.

@dick_freebird - output of the controller is unregulated and not fix whereas the battery is an LFP one. As I understand, and from some damaging experience, that I cannot just let unregulated voltage feed the LFP battery pack. Hence the need for this circuit. If you read the original post, there's a buck-boost controller as well feeding the battery to ensure that the output to the battery is regulated.

There is another thread discussing ideal diodes:

https://www.edaboard.com/showthread.php?381734-Protection-of-15A-DC-power-line&p=1637071#post1637071