How Can You Build a 3V Battery Indicator Without a Zener Diode?

[theloathedone]

Hi,

I'm not sure if this is the right place to post this, but here goes.

I'm trying to build a battery indicator circuit for 2 AA batteries (3V). So far what I've read online is that I'd need to use a Zener diode to get a fixed voltage drop, then connect it to a transistor, like the diagram here:
http://www.4qdtec.com/batty.html"

Only problem is, the smallest Zener diode is 2.4V, so the difference between the base and the emitter would be very small - 0.6 V - even when the battery is fully charged.

Will this work?

 

[Drakkith]

If you don't get help here, try the Electrical Engineering forum. They should be able to help you there.

 

[Sciurus]

Are you looking at this schematic?

Typical diodes have a 0.6-0.7 V drop when forward biased, so you could use a few of those in series.

 

[theloathedone]

Yup I'm looking at that schematic, which is for a 6V battery.

Thanks Sciurus, I didn't think of that even though I have a few diodes lying around. So I guess instead of a Zener diode in reverse bias, I could just use (say 3) normal diodes in forward bias to get a 2.1V voltage drop, so the voltage difference between the base and the emitter is around 0.9 V when the battery is fully charged, and decreases as the battery is drained?

 

[pmacias]

Or do I need a different circuit?

Hello,

I would suggest considering a different circuit design that takes into account the limitations of the Zener diode. One potential solution could be to use a voltage divider circuit with resistors to create a reference voltage that is lower than the 3V battery voltage. This reference voltage can then be compared to the battery voltage using a comparator circuit to determine the battery level. This approach would not rely on the use of a Zener diode and would allow for a larger voltage difference between the base and emitter of the transistor. Additionally, using a microcontroller with an analog-to-digital converter could also be a more accurate and versatile solution for measuring the battery voltage. I would recommend researching different circuit designs and consulting with experts in the field before proceeding with your project.