LM317 with automatic low cut off

Thread Starter

bend94

Joined Feb 15, 2016
17
Hi,

I am building a simple DC 12v DC in 9v DC out.
I have been using an LM317 and its been fine.

Now I require the output to cut out if the input voltage drop below 10v.
With a draxning please
Thanks in advance for your help!
 

AnalogKid

Joined Aug 1, 2013
8,224
To do this you will have to add a comparator to the input. Why don't you sketch up a block diagram or schematic for us to review.

Also, what do you mean by "cut out"? An LM317 has a minimum output voltage of 1.25 V. You can not turn the output down to zero volts without more modifications to the standard regulator circuit.

ak
 

hp1729

Joined Nov 23, 2015
2,304
To do this you will have to add a comparator to the input. Why don't you sketch up a block diagram or schematic for us to review.

Also, what do you mean by "cut out"? An LM317 has a minimum output voltage of 1.25 V. You can not turn the output down to zero volts without more modifications to the standard regulator circuit.

ak
I think what he is looking for is the output to go to zero, not just go unregulated or drop to 1.25. Disconnect the input if it drops below 10 V?
 

Wendy

Joined Mar 24, 2008
21,914
Something you need to be aware of, the LM317 drops around 2V just doing its job. So if you have 10V in you will have 8V or less out.

There are families of more modern 3 terminal regulators that drop a lot less voltage. A good resource on this site is Components Selection Guide.

If you want I will draw something up to get you started. I suspect you need to address the other problem first though.

Just a thought, a simple zener circuit might work better for the regulator, depending on what your current requirement for your circuit is.
 

Thread Starter

bend94

Joined Feb 15, 2016
17
Hi again

Please find my actual electronic device that i am using
I power my arduino with solar energy. it is working correctly till the battery has enough energy.

My goal is to stop powering my arduino when to battery is to low
Because with this actual LM317 when battery power is too low
the arduino is powerup / powerdown / powerup / powerdown all the time.

I want to stop when low power to avoid damage on my arduino.

upload_2016-2-16_10-2-42.jpeg

Please help

thanks
 

Dodgydave

Joined Jun 22, 2012
8,575
You can use a TL431 programmed zener and p_fet or opto coupler to turn off your Arduino, you set the desired voltage using two resistors.
 

Thread Starter

bend94

Joined Feb 15, 2016
17
i will like arduino to stay off until sunshine and battery is recharged enough to power the arduino
so not manually but if possible automatic

thanks
 

AnalogKid

Joined Aug 1, 2013
8,224
To do what you want requires two things, a comparator to sense the voltage out of the Regulator, and either a power switch or a control signal output that shuts down the system. What is the circuit or device inside the box called Regulator? If this has a shutdown control pin, it makes things easier.

i will like arduino to stay off until sunshine and battery is recharged enough to power the arduino
Automatic restart is not a problem. Do you want the system to restart as soon as the solar panel output is high enough to run the system, or wait until the battery is recharged enough?

ak
 

Thread Starter

bend94

Joined Feb 15, 2016
17
my device will be connected to the solar regulator output .
This output deliver 12V DC . Well i would like to restart when the solar output is delivering 12V DC
 

Thread Starter

bend94

Joined Feb 15, 2016
17
The Regulator is a solar regulator without any shutdown control pin

>a comparator to sense the voltage out of the Regulator,
Is it possible to do so, with a NE555 ?
 

Alec_t

Joined Sep 17, 2013
10,594
It's possible, but a comparator IC such as the LM339 would be much more convenient since it is easier to define reference voltages.
 

bertus

Joined Apr 5, 2008
20,179
Hello,

The NPN transistor will short the output of the regulator and cut the poser for the 555.
This circuit will probably oscillate.

Bertus
 

Alec_t

Joined Sep 17, 2013
10,594
Same problem with a relay, if you use it to short the output of the 7809.
There is also some uncertainty as to the switching thresholds in that circuit, since if the 7809 input drops below the point where regulation fails, the 7809 output will drop too, and so the thresholds will be 2/3 of ??? and 1/3 of ???.
 
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