Application about TL431.

chao yang

Other Parts Discussed in Thread: TL431, TMS320F28069M

Hello all

I am a beginner.In my application,I need to change 36-120V input to 2.5V output as high level of microcomputer and change 0V input to 0V output as low level of microcomputer.

For reasons of cost,I want to use TL431 to do this.So What I designed circuit is as follows:

I'm not sure if it's correct.Could anyone give me some advice? Thanks

chao

over 10 years ago

0 Ron Michallick over 10 years ago

TI__Guru**** 165036 points

Chao,

Your circuit matches the requirement listed.
Is there a requirement for input voltage between 0V and 36V?
Does the output load draw any current?

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

Expert 1620 points

Is there a requirement for input voltage between 0V and 36V?

Don't care about it. If input voltage is less than 36V,then the system will start the under-voltage protection.

Does the output load draw any current?

The "OUTPUT" connects directly to GPIO pin of the TMS320F28069M.

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

TI__Guru**** 165036 points

Chao,

It should work well.

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

Expert 1620 points

Ron

I found maximum value of Vka from datasheet is 37V,But my INPUT is 36V - 120V.Can TL431 be damaged?

chao

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

TI__Guru**** 165036 points

Chao,

It could be damaged if the voltage became that high.
But why would the voltage ever exceed 2.5V?

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

Expert 1620 points

But why would the voltage ever exceed 2.5V?

Sorry,I am not clear about this problem. I need that when Input of system is 36-120V,I can convert the voltage into 2.5V,then send the 2.5V to GPIO pin as high level.

when Input of system is 0V,I can convert the voltage into 0V,then send the 0V to GPIO pin as low level.

But when I use TL431 to do this,I have a problem : maximum value of Vka is 37V,but my input voltage is 36 - 120V.I fear that TL431 will be damaged.

So I need help.Did you have other suggestions to me?

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

Expert 1620 points

I designed a new circuit：When INPUT is 36V-120V,I made GPIO high level.When INPUT is 0V,I made GPIO low level.

What do you think about that ? Is it right?

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

TI__Guru**** 165036 points

Chao,

TL431 voltage won't exceed 2.5V unless there was an open solder joint or some other board defect.

36V to 120V input will make GPIO about 5mV.
0V input will make GPIO 3.3V

Power management

Power management forum

Application about TL431.