Battery voltage Cut off circuit Simulation help needed ?

Thread Starter

mishra87

Joined Jan 17, 2016
701
Hi Guys,

I want to cut the battery power supply as per attached circuit.
Now the problem with this circuit MCU will not wake up since MOSFET will not get turned ON because charging MOSFET is not switching ON due to mosfet will not turned ON.

Could anybody suggest me some circuit for the same ?
The intention of this circuit is that first charger give supply the microcontroller power supply and once MCU start working it will wake up and then MOSFET M1 turned ON and battery start charging.
 

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AlbertHall

Joined Jun 4, 2014
9,665
As you have V3 connected across the output this will prevent the output voltage ever changing. Simulated voltage sources have zero resistance by default. If you right click the source and go to advanced properties you can specify an internal rresistance.
 

jpanhalt

Joined Jan 18, 2008
9,125
Are you asking how to disconnect the battery when the external supply is attached? I don't think I understand your question.

1) Having the battery connected to the external supply without some sort of charger for protection is not a good idea.
2) If you want the battery to be disconnected when the external supply is attached, you can modify this common approach with a P-mosfet:

1590229110810.png
Ignore IC1. Notice how attaching the external supply is used to disconnect the battery. There are several variations of that design. That is just one that was convenient.
 

Thread Starter

mishra87

Joined Jan 17, 2016
701
Are you asking how to disconnect the battery when the external supply is attached? I don't think I understand your question.

1) Having the battery connected to the external supply without some sort of charger for protection is not a good idea.
2) If you want the battery to be disconnected when the external supply is attached, you can modify this common approach with a P-mosfet:

View attachment 207903
Ignore IC1. Notice how attaching the external supply is used to disconnect the battery. There are several variations of that design. That is just one that was convenient.
Thanks for your reply.

I wanna say some basic points.

My charger is already design for CC/CV operation so there is no issue if charger is directly connected to battery

Since i am driving transistor Q1 and then M1 from microcontroller so lets say if battery is below threshold level and then it will not able to give supply for microcontroller in that case micro will be dead.
Now if i connect charger using this circuit since M1 is not working and hence battery will not get any voltage to charge it because M1 is open.
So i wanted with the help of this circuit that the charger power supply first give power supply to microcontroller unit (buck circuit) and then micro will start working. Now micro will give signal to Q1 to turn ON M1 and battery is being charged.

That is the idea.

Reason for using PWM signal to drive the mosfet is to control the charging current of charger based on battery pack of temperature.

hope this will clear the requirement .

Thanks in Advance !!!
 

Thread Starter

mishra87

Joined Jan 17, 2016
701
As you have V3 connected across the output this will prevent the output voltage ever changing. Simulated voltage sources have zero resistance by default. If you right click the source and go to advanced properties you can specify an internal rresistance.
Thanks for reply.

I already explained in thread#4
 

Thread Starter

mishra87

Joined Jan 17, 2016
701
I created some block diagram to switch the battery charger current using PWM signal from MCU.
Now the problem is if battery is dead how do we generate the power supply of for microcontroller .
Will this circuit is feasible ???
1590259179781.png
 

jpanhalt

Joined Jan 18, 2008
9,125
What's the function of the mosfet? That circuit looks like it will operate the same with or without it.

Or, should the "MCU Wakeup Power Supply" be another box? Is there a steering diode between the battery and the MCU Power Supply (anode at the battery)?
 

Thread Starter

mishra87

Joined Jan 17, 2016
701
What's the function of the mosfet? That circuit looks like it will operate the same with or without it.

Or, should the "MCU Wakeup Power Supply" be another box? Is there a steering diode between the battery and the MCU Power Supply (anode at the battery)?
What's the function of the mosfet? That circuit looks like it will operate the same with or without it.

Or, should the "MCU Wakeup Power Supply" be another box? Is there a steering diode between the battery and the MCU Power Supply (anode at the battery)?
What's the function of the mosfet? That circuit looks like it will operate the same with or without it.

Or, should the "MCU Wakeup Power Supply" be another box? Is there a steering diode between the battery and the MCU Power Supply (anode at the battery)?
The function of this mosfet is to switch the charging voltage to battery. The mosfet gate is controlled by PWM of microcontroller and that is how we control the charging current.

Actually i do not know where do i connect diode,
The problem i see with this circuit lets say battery is discharged below threshold level so no power supply for MCU(microcontroller Unit) so no signal at at gate of mosfet and mosfet will not turned ON to switch the supply from charger to charge the battery.

Now once i connect the charger first charger supply should go to mcu to make sure mcu is in working mode.Once mcu start working it can control the mosfet.

So that is idea was and i am not sure if it is correct ?
 

jpanhalt

Joined Jan 18, 2008
9,125
The red line bypasses the mosfet, unless you have a diode as I described or the wake-up supply is another box. If it is another box, then you have to be sure the voltage regulator it presumably has will tolerate Vout>Vin.

1590262874396.png
 

Thread Starter

mishra87

Joined Jan 17, 2016
701
The red line bypasses the mosfet, unless you have a diode as I described or the wake-up supply is another box. If it is another box, then you have to be sure the voltage regulator it presumably has will tolerate Vout>Vin.

View attachment 207951
Thanks for your great time and help.
At the moment i am looking for wakeup supply along with mosfet circuit.

Could you please draw some block diagram which include wakeup supply and battery charging current control circuit ?

Thanks again for help.
 
This how it could be done... when charger is attached it drives MCU and battery is charged independently. There are inherent issues with your design. Since MCU is driven off charger circuit the charger may never terminate charge after CV phase as it always sees MCU regulator current drain - unless this is << charger cutoff current. Also some chargers may not provide any output voltage if they don't see some battery voltage on connection so this bootstrap may not work - R1 allows charger to 'see' some battery voltage; it should be big enough not to effect charging process while enabling charger operation. Your battery should never be depleted below 6 - 7v else it could be dangerous (when recharged). Ideally you should have discharge protection Mosfet on output side of battery that turn off supply to MCU if battery volts < 6v say.

reg.JPG
Can't help but think that a 2S battery management chip with integrated mosfets would be a better/simpler long term solution (along the lines that jpanhalt suggested earlier).
 
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