Hi there, this has got to be a common problem but I can't find a solution online.

I am looking for a simple IC that can cut supply when voltage drops to low.
One AA battery is discharged at 1.3V so if I have 4 in series I want to cut power at 5.2V. I don't want my circuits going below 5V either so its a double bonus if I can just cut the power.

In the past I have tried making my own using transistors, zenor diodes and even a comparator circuit. I found the results to be very unstable with temperature changes and some of the circuits just ate a lot of power.

What do manufacturers normally use as there are plenty of devices that run off 4 AA batteries? Surely there's some neat little chip I can buy and move on to more important parts of the circuits I build.

Any help would be appreciated.

 

Hi there, this has got to be a common problem but I can't find a solution online.

I am looking for a simple IC that can cut supply when voltage drops to low.
One AA battery is discharged at 1.3V so if I have 4 in series I want to cut power at 5.2V. I don't want my circuits going below 5V either so its a double bonus if I can just cut the power.

In the past I have tried making my own using transistors, zenor diodes and even a comparator circuit. I found the results to be very unstable with temperature changes and some of the circuits just ate a lot of power.

What do manufacturers normally use as there are plenty of devices that run off 4 AA batteries? Surely there's some neat little chip I can buy and move on to more important parts of the circuits I build.

Any help would be appreciated.

I use a switcher to provide constant volts until battery end-of-life.

 

Hi thanks for replying, what is a switcher?

 

Below is the schematic and LTspice simulation of a battery cutoff circuit that uses a low-power TLV431 voltage reference as a comparator with a P-MOSFET to disconnect the battery load (yellow trace) at 5.2V (blue trace)
This voltage is adjustable by pot U2.

The TLV 431 Ref voltage is quite stable with temperature.
It turns off the MOSFET when the input Ref voltage goes below 1.2V.

The circuit draws only about 0.25mA during operation.

The P-MOSFET must be a logic-level type (Vgs threshold of ≤2V).

 

Below is the schematic and LTspice simulation of a battery cutoff circuit that uses a low-power TLV431 voltage reference as a comparator with a P-MOSFET to disconnect the battery load (yellow trace) at 5.2V (blue trace)
This voltage is adjustable by pot U2.

The TLV 431 Ref voltage is quite stable with temperature.
It turns off the MOSFET when the input Ref voltage goes below 1.2V.

The circuit draws only about 0.25mA during operation.

The P-MOSFET must be a logic-level type (Vgs threshold of ≤2V).

View attachment 165810

Hi Thank you for your reply, I had come across the TL431 and had been put off a little by the bottom reply in this thread https://electronics.stackexchange.com/questions/213304/tl431-low-battery-cut-off

However your demonstration does look very good and I am more than willing to give it a go. My only quibble would be regarding Hysteresis. Would I have to add in a Schmitt trigger or something similar to stop the transistor oscillating as the voltage will rise slightly when the load is shed?

 

I had come across the TL431 and had been put off a little by the bottom reply in this thread https://electronics.stackexchange.com/questions/213304/tl431-low-battery-cut-off

I'm using the TLV431 which is a low-current version of the TL431.
That version will sharply switch the MOSFET on and off.

My only quibble would be regarding Hysteresis.

Hysteresis is supplied by the positive feedback through R4.
Note the difference in switch points for the positive and negative going transitions (about 175mV).
That's the value of the hysteresis.
That can be changed by using a different value for R4, if needed.

Edit: To answer your other question, a switcher is a switching power supply that can efficiently convert one DC voltage to the other.
It his case you would need a buck-boost type converter which could maintain the 5V output down to about 4V input or below, where the batteries are essentially dead.

Alternately you might be able to use just a boost converter, which would kick in when the battery voltage drops below 5V.

 

Thanks again for your help, that all makes a lot more sense. I'm a bit of an electronics nube when it comes to circuit design so I'm still building up on experience.

Had a quick look at the TLV431, I might try it out at some point but on a quick calc, ignoring load the circuit you posted will run for 5200 hours with 1300mAH AA (4 in series that is) so I think that should carry me through.

Aha switcher is a buck boost. hadn't heard it called that b4. I think I would use a buck to get the steady 5V output but I wouldn't want to run the battery's much lower than 5.2V. I often use rechargeable and I burnt through a set testing a few circuits, gets a bit expensive.

I think what you have taught me here should see me through a good number of battery powered projects

Many Thanks and kind regards
Will

 

I wouldn't want to run the battery's much lower than 5.2V. I often use rechargeable and I burnt through a set testing a few circuits

What type of rechargeables?
Four NiMh in series only give about 4.8V.
Five in series would give 6V nominal.