Hi,
I would like to be able to force the MOSFET on in my LM5050 active diode circuit as needed.
In some conditions I need it to act as an active diode, in some conditions I need for the MOSFET to conduct current in the other direction. This decision will come from an MCU.
Below is my schematic. I force the LM5050 to turn on the MOSFET regardless of current direction by pulling the OUT pin down by 1 diode drop.
The JFET is a constant current source at 0.5 mA, which degenerates to a 250 Ω resistor below 125 mV drop.
When the BJT is off the JFET looks like a 250 Ω resistor and the LM5050 acts like an active diode controller. (OUT pin current max is 8 uA, which yields 2 mV drop)
When the BJT base is driven to 3.3V it looks like a 0.9 mA current sink into the Collector. This is greater than the 0.5 mA of the JFET. The other 0.4 mA flows through diode D2 which limits the voltage at 0.7V.
This 0.7V forces the LM5050 to drive the MOSFET fully on regardless of the load current direction.
"BOOST_OUT" is a 48V battery pack which is always present. Lightning surge may cause 95V spikes (there is a protection circuit not in the schematic).
To the left of the schematic, not shown, is a boost converter.
My questions are:
1) Is it OK for the LM5050 to see 1.8V max from IN to OUT pins?
2) Do you see any problem with my circuit? I have already done some testing and it seems to work as expected. The OUT pin does not appear to draw abnormal currents when the BJT is on.
Thanks,
Jason
