Some things like calculator and TV remote have special circuit inside and this Battery Saver Circuit help to protect battery; also if someone forget to turn OFF the circuit, then it stops 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 and also it uses one FET transistor T1 as regulator and allow max 150 mA current.
Hence, if device uses more than 100 mA then better to use stronger FET not BS250.
Circuit Working:
Parts List:
| Components | Values | 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 |
To begin with, when device stay ON by mistake this circuit help stop battery from draining too much which works like battery saver.; also 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.
Also, 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 and hence, this charging goes for one minute.
After one minute voltage on R3 goes down so N3 will see low signal at pin 1, then N3 changes its output and T1 turn OFF and also N2 help keep N3 stable and stop it from jumping around when voltage changes.
Furthermore, R1, R2 and C1 give strong pulse to N2 when power goes OFF to clear any charge in C2.
Also, switches S2 and S1 can turn circuit back ON quickly and still save battery.
Here, NAND gate N4, diode D3 and resistors R5 and R6 watch battery voltage carefully and N4 trigger level is same as supply voltage level.
Hence, when battery is good N4 see low level at R5 and R6 point and diode D3 keep voltage at N4 input safe when battery drop low so wrong signal does not happen.
Formula:
Below 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 and 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 and 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, hence, many things affect battery like temperature, apps running, network signal, screen brightness and more.
Most people use discharge safety to avoid deep drain and 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 and so battery life may be different.
How to Build:
Below is the process of how to build Battery Saver Circuit:
- First, connect the battery and be sure battery (+) and (–) connect to correct place in circuit.
- Then the logic part uses NAND gates with Schmitt trigger like N3, N4 and N2, so follow steps from circuit to connect input and output of each gate.
- After that, connect P-channel FET T1 as per pin layout and ensure N3 output goes to right place on T1.
- Next, connect resistors R1, R2, R3, R5 and R6 as shown in diagram and use right values for resistors based on circuit need.
- Also, place capacitors C1 and C2 in correct place like in circuit diagram and choose capacitor value as per circuit design.
- Now if battery voltage drops, then D3 will help protect N4 input and after that connect diode D3 properly.
- Next, use switches S1 and S2 to turn ON/OFF and reset circuit and connect them as needed.
Testing Circuit:
- After building test everything and check if circuit turn OFF after 1 minute and reset work is fine; also be sure power down happens the right way.
Make Changes if Needed:
- Remember, if something is not right for the use then change resistor or capacitor value.
Conclusion:
Overall, this Battery Saver Circuit turn OFF power after 1 minute or if battery goes too low, it also help save battery and stops over-discharge.
Finally, this circuit is very useful for safe and smart battery use.
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