TL431 for TDA1541 does not work

[Bernhard]

Hi,

is it right that the pin numbers of the TL431 read 123 as the pins of a BC550 read CBE ?

Is it right that the output voltage should be 5V independent of the input voltage when R1/R1 are 1k ?

Does the TL431 need a minimum load current ?

Bernhard

 

[Peter Daniel]

http://rocky.digikey.com/WebLib/Texas Instruments/Web data/TL431,431A.pdf

As to your second question: it is true.

 

[Bernhard]

I built a test circuit, the resistor to pin 1 is 39ohm R1/R2 are 1k.
Input voltage is 8V.

I increased to 10V.

Sometimes it is 7,6V output and sometimes 5V. If 5V then it depends on input voltage. Higher input = higher output.

Maybe Ikilled that with soldering ? Never happend before.

 

[Peter Daniel]

The series resistors have to be calculated to provide enough voltage drop. This drop depends on the current draw after regulation. If the drop isn't correct, then you may be getting more than required 5V.

 

[Bricolo]

The series resistors have to be calculated to provide enough voltage drop. This drop depends on the current draw after regulation. If the drop isn't correct, then you may be getting more than required 5V.

if the series resistor is too small, the 431 won't last long 😀

 

[Bernhard]

Thanks Peter,

I got a damn strange data sheet before...

http://www.componentkits.com/dslibrary/TL431.pdf

In the schematic that I use from K. Boehm ref =3, in the data sheet ref = 1 *ggg*

Also in that data sheet most values are only a fat point 😕

Turned the TL around and it works now, 5,0007V with 0,5% resistors.

Other question: What happens if this little thingy fails ?

Will it take the S1 to hell ?

 

[guido]

Thanks Peter,

Other question: What happens if this little thingy fails ?

Will it take the S1 to hell ?

No, they go to heaven!

 

[Bernhard]

May be put 1W zeners everywhere...