Some things like calculator and TV remote have special circuit inside and this Battery Saver Circuit help to protect battery.
If someone forget to turn OFF the circuit stop battery to finish fast.
But still battery will lose power slowly with time even with this circuit.
The Circuits Goal:
After one minute ON or if battery voltage goes low than set level then this battery saver circuit quickly stop the current.
It uses one FET transistor T1 as regulator and allow max 150 mA current.
If device uses more than 100 mA then better to use stronger FET not BS250.
Circuit Working:
Parts List:
| Type | Description | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt) | 1M | 1 |
| 10M | 1 | |
| 2.2M | 1 | |
| 22k | 1 | |
| 3.3k | 1 | |
| 100k | 1 | |
| Capacitors | Ceramic 1nF | 1 |
| Electrolytic 22µF 25V | 1 | |
| Semiconductors | MOSFET BS250 | 1 |
| IC 4093 | 1 | |
| Diode 1N4148 | 2 | |
| Zener Diode 6.8V | 1 | |
| ON/OFF Switch | 1 | |
| Push to OFF switch | 1 |
When device stay ON by mistake this circuit help stop battery from draining too much which works like battery saver.
NAND gate N3 stay high when power turns ON.
This happen because resistor R6 keep input of N4 low when capacitor C2 is empty at start.
In this time P-channel FET T1 is ON so current can flow and give power to device.
When T1 is ON capacitor C2 start charging through resistor R3.
This charging goes for one minute.
After one minute voltage on R3 goes down so N3 see low signal at pin 1.
Then N3 changes its output and T1 turn OFF.
N2 help keep N3 stable and stop it from jumping around when voltage changes.
R1, R2 and C1 give strong pulse to N2 when power goes OFF to clear any charge in C2.
Switches S2 and S1 can turn circuit back ON quickly and still save battery.
NAND gate N4, diode D3 and resistors R5 and R6 watch battery voltage carefully.
N4 trigger level is same as supply voltage level.
When battery is good N4 see low level at R5 and R6 point.
Diode D3 keep voltage at N4 input safe when battery drop low so wrong signal does not happen.
Formula:
This formula help to find how long battery can work:
Battery life = Capacity / Consumption × (1 – Discharge safety)
What it means:
Battery life tell how many hours (h) battery will last.
Capacity is how much charge battery can store and it is in mAh or Ah.
Consumption is how much current device it uses and it is in mA or A.
Discharge safety is number we use to keep battery safe so we do not want battery to go fully empty.
How formula works:
Capacity ÷ Consumption:
This part tell us how long battery will last if we use full charge.
Discharge safety:
This part save some charge in battery where we do not use full battery to make battery life longer.
Important to remember:
This is just an estimate but real battery life can change.
Many things affect battery like temperature, apps running, network signal, screen brightness and more.
Most people use discharge safety to avoid deep drain.
Some battery datasheets give better discharge level for longer battery life.
This formula also think device always use same current but in actual life current goes up and down.
So battery life may be different.
How to Build:
Below is the process of how to build Battery Saver Circuit:
Connect Power Source:
- First connect the battery and be sure battery (+) and (–) connect to correct place in circuit.
NAND Gates with Schmitt Trigger:
- The logic part uses NAND gates with Schmitt trigger like N3, N4 and N2.
- Follow steps from circuit to connect input and output of each gate.
P-Channel FET T1:
- Connect P-channel FET T1 as per pin layout.
- Ensure N3 output goes to right place on T1.
Connect Resistors:
- Connect resistors R1, R2, R3, R5 and R6 as shown in diagram.
- Use right values for resistors based on circuit need.
Connect Capacitors:
- Place capacitors C1 and C2 in correct place like in circuit diagram.
- Choose capacitor value as per circuit design.
Connect Diode D3:
- If battery voltage drops D3 will help protect N4 input.
- Connect diode D3 properly.
Connect Switches S1 and S2:
- Use switches S1 and S2 to turn ON/OFF and reset circuit.
- Connect them as needed.
Testing Circuit:
- After building test everything.
- Check if circuit turn OFF after 1 minute and reset work is fine.
- Be sure power down happens the right way.
Make Changes if Needed:
- If something is not right for the use then change resistor or capacitor value.
Conclusion:
This Battery Saver Circuit turn OFF power after 1 minute or if battery goes too low.
It help save battery and stop over-discharge.
This is very useful for safe and smart battery use.