TL431 Voltage monitor

Jayamohan Muthusamy

Prodigy 115 points

Other Parts Discussed in Thread: TL431, TLVH431

Hi,

I need voltage monitor with LED indication for monitoring 24V battery.

When the battery voltage drops below 18V the LED should get ON.

I referred TL431 in fig.26 of attachment.

My doubt is, how to calculate Vref? Is this fixed 2.5V or something else...

Kindly guide me on choosing resister also.

7802.TL431-D.pdf

Regards

Jayamohan.M

over 10 years ago

0 Ron Michallick over 10 years ago

TI__Guru**** 152406 points

Jayamohan,

Vref will be 2.5V in the equations.

Because you only need a low indication, use can use just 1 TL431 plus some other components.
Attached is a lightly tested, design using TI-Tina (free application)

LT_18V_LED.TSC

0 Ron Michallick over 10 years ago in reply to Ron Michallick

TI__Guru**** 152406 points

To lower LED off current demand, U1 can be replaced with TLVH431 and R3 can be increased.
Note the cathode voltage is limited to a low value by T1 and LED1.

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TL431 Voltage monitor