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Precise voltage reference

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adrianvon

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Hi,

I need a device to set a precise 4.7V (or a close value) output for reference set-point. The input will be between 4.8V to 5.2V. The problem is keeping a constant 4.7V at the output no matter of the input voltage tolerance.

I found this component which can help me achieve this:

**broken link removed**


Unfortunately I found no tutorials on such components.

Thanks in advance.
 
Check out the TL431 and similar, commonly used in TV and VCR etc. PSU's (so easy to find one).

It's basically a 2.5V precision reference, but you can add a pot to make it variable from 2.5V upwards.

I used one in my analogue PIC tutorial:
 
Update: I managed to understand the datasheet. Apparently to set the output voltage it make use from external resistors which are connected to the input sully (i.e. unregulated supply). Will this cause variation in the output if the input varies?
 
Also, is there a voltage drop on such devices? Like when using the 7805 regulator, the input must be approx. 2V higher than the input. Does this apply for these components as well?
 
Here's an example to show the use of a TL431. R2 and R3 set the voltage V(ref) you want. They form a voltage divider such that the control input of the IC is 2.5V. The graphs show how V(ref) varies as the supply voltage goes from 0 to 10V.
TL431A_use.gif
 
Thanks a lot for the reply. Since the output will be connected to a 1Kohms potentiometer, is there the need to use R1? The datasheet states that R1 is used to set a current of 1mA or higher to the cathode of the component.
 
Thanks a lot for the reply. Since the output will be connected to a 1Kohms potentiometer, is there the need to use R1? The datasheet states that R1 is used to set a current of 1mA or higher to the cathode of the component.

Yes, it's absolutely 100% VITAL - it's a shunt regulator, without a current limiting circuit (in this case the resistor) it will instantly destroy itself. You need to chose the resistor based on the supply voltage, the reference voltage you're looking for, the load current, and the current through the device (should be a minimum of 5 times the load current).
 
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