Circuit to automatically connect to vcc

Other Hardware General Electronics
1

Hello, I am designing a system to power a atmega328. I will use a litio battery(3,7V) and a mcp73811 to charge the battery.
I would like to make a circuit capable of cutting the feed below 3V and that is activated above 4V.
I thought about doing it with a comparator operational, but the reference voltage comes from the battery, so, the reference voltage would look affected by decreasing the voltage of the battery.
Any solution?

Thanks,
Regards.

2

You can have a cutoff circuit using a zener diode as the reference voltage(s)

3

composition4:
You can have a cutoff circuit using a zener diode as the reference voltage(s)

Although to save power when cut off you will want to run the zener at a very small current, which will mean the
voltage across it will be rather less than its nominal value - some experimentation might be needed.

Another option is to find a precision voltage reference that works at very low current (10uA or similar) - combine
this with a micropower comparator and high-value resistor divider...

4

chstr:
Hello, I am designing a system to power a atmega328. I will use a litio battery(3,7V) and a mcp73811 to charge the battery.
I would like to make a circuit capable of cutting the feed below 3V and that is activated above 4V.
I thought about doing it with a comparator operational, but the reference voltage comes from the battery, so, the reference voltage would look affected by decreasing the voltage of the battery.
Any solution?

Thanks,
Regards.

Some Li-po cells have a built in protection circuit to switch off the battery if it's cell voltage drops to 3vdc or lower. Check the sparkFun site, I think some of their cells offer this built in protection.

Lefty

5

The processor has a 1.1V reference voltage, can't you use that?

This sketch outputs that reference voltage on the AREF pin:

// Find internal 1.1 reference voltage on AREF pin
void setup ()
{
  analogReference (INTERNAL);
  analogRead (A0);  // force voltage reference to be turned on
}
void loop () { }
6

Hello, thanks for reply. I'm looking for information from your comments. Then, I will put my doubts. thank you very much.
Regards.

7

The information is there, like the Force.

8

Hello, thank you very much everyone for the information. I go by parts:

  1. To charge the battery I will use the MCP73831 (Programmable Charge Current: 15 mA to 500 mA)
  2. To detect the low battery, I can use the MAX8211 or STM809 (with VRST = 2.85V to 3.00V). Then, I can connect the output of low battery to a mosfet to cut the feed,What do you think about this solution? Although, I do not know how reactivate the circuit.
  3. I did not find how to design a PCM circuit. I will keep looking.

Thanks,
Regards.