I have a 12V li-ion battery that I am trying to protect from draining below 9.3V
I selected MIC2776H-YM5 to monitor voltage and followed the datasheet:
I used the equations in the data sheet to select my R1 and R2 for the voltage divider to get 9.3V as my threshold such that the RST pin goes high when voltage falls below this value.
I am using P-channel IRF5806PbF mosfet to essentially switch off my load using the high signal from the voltage monitoring IC going to the gate of the mosfet.
I have attached a picture of my circuit and there are some notes on the picture.
What I am experiencing is the voltage monitoring IC getting really hot and in some cases releasing the "magic smoke."
Can someone please advise where I went wrong? It would be a huge help...
So any suggestions on how I might be able to make this work?
I don't necessarily want to use another voltage divider to get the Vdd down to 5V as that voltage will drop with the battery voltage dropping... which would result in RST voltage dropping... and come to think of it when the RST pin gets pulled high even at 5V this probably won't fully turn off the P channel mosfet...
Perhaps I should move to an N channel mosfet and low side switch it with the active low version of this device... I have to see if that makes sense later while my wife isn't yelling at me to get off the computer. In the meantime if you guys have any suggestions let me know. Thanks!
And the p channel is the same, the n channel is BSS123:
The monitor IC should pull the output to a low voltage when battery level drops below ~9.3V ... thereby opening n channel mosfet and forcing p channel gate high which kills the load... in theory.
Can anyone see any issues with this approach? Thanks!
I guess that in this sort of application, the leakage currents of the various components have to be factored in, for example mosfet drain/source leakage. I haven’t done this but I may have considered some sort of latch between the battery and the supervisor circuit which, once broken, had to be explicitly reset. The benefits of this depend of course on how long the battery could be left in a discharged state and its self discharge rate etc. etc.
How, incidentally, are you going to integrate a charging circuit?
This is for a Milwaukee M12 tool battery that I'm using to power some portable LED lights.
When you say leakage currents, I'm assuming you mean the currents still being drawn by the voltage dividers / pull up resistors etc that remain while the P channel has shut down the main load? If so I'm not too worried about those as the batteries are removable tool batteries. So the user will just pop them out of the portable light when they go dead.
As for charging... since they are tool batteries, the dedicated charging stations will charge the battery so luckily I don't have to worry about that in here
OK. All is clear. If these are manually switched LED lights, then maybe put the switch as (electrically) near to the battery as possible. However, it does appear that the self discharge rate of those batteries probably dwarfs all the other leakage considerations so there may not be much to be gained from optimisation measures.
Hi,
If you look at your original circuit, you have the MOSFET connected the wrong way around.
Even with the MOSFET OFF, you will have current flowing through the built in protection diode.
The circuit in post#4 has the MOSFET configured in the correct direction.
