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Programmable Voltage Reference TL431IZT , what does it do?

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At my work they use Programmable Voltage Reference chips TL431IZT for the IC chips around a CPU microcontroller

They use a Programmable Voltage Reference TL431IZT to power a SC-531P Oscillator 8.0 MHZ

But why did they use a Programmable Voltage Reference TL431IZT , what does it do? why didn't they just use a voltage divider with resistors and trim pot?

If you put a lot of load on the output of a TL431IZT it doesn't drop the voltage? why is that? is it like a regulator?

What have you seen Programmable Voltage Reference used for? why did they use them?
 
Billy,

I have seen many posts from you asking all of us to educate you. I suspect you can read just fine, so start by reading the Data Sheet for the TL431.
 
The datasheet doesn't explain much, I didn't get much out of it when I read it, plus it's a complex circuit that's inside.
 
I do have the datasheets, I'm just confused as To why someone would use these , for what use when you can use a voltage regulator or switching regulator instead.

When have you seen these programmable voltage references used for? for what kind of IC chips and for what kind of circuits?
 
The simplest way to look at the TL431 is as an adjustable zener diode. And, like a zener it really does not have an 'output' terminal.

It typically has a resistor divider to 'program' the zener voltage across a wide range. You can connect the ends of the divider to the cathode and anode pins of the TL431 and make a two terminal zener. When the voltage at the junction of the divider is less than 2.5V, the cathode-anode won't draw much current. If that junction voltage is above 2.5V, the cathode-anode will draw current.

But you can also tie the top of the resistor divider to one place, and the cathode to another. This is the typical configuration in many power supplies. The resistors sees the output voltage, and feeds the error signal back to the voltage control loop of the supply.

The TL431 is probably in more power supplies world wide than any other single component.
 
wouldn't using a trim pot tied to the supply and an zener diode be a adjustable zener diode too?

I don't see how it's any difference or what good of use it can be

I'm still confused about it
 
wouldn't using a trim pot tied to the supply and an zener diode be a adjustable zener diode too?

no. Zeners are not adjustable. That is why the TL431 was made. It is much better at regulation than a Zener. The TL431 is better with temperature.

I don't see how it's any difference or what good of use it can be

On a board you might need a 5.1V and a 6.8V and a 12V Zener. Three different parts.
With TL431 you need more resistors but you only have to change one resistor to make the same part do all three jobs above.
 
so what's the difference between a regulator or using a regulator VS a programmable voltage reference?

I don't understand the difference between the two

It's an adjustable zener diode with a buffer?
 
so what's the difference between a regulator or using a regulator VS a programmable voltage reference?

I don't understand the difference between the two

It's an adjustable zener diode with a buffer?

No, it's a MUCH better zener diode (an adjustable SUPER zener) with a buffer - if a zener is a pair of roller skates, a TL341 is a Mercedes.

The clue is in it's title - PRECISION adjustable voltage reference.
 
If you look at the temperature stability of a typical regulator or zener, and the temperature stability of a voltage reference you will see the difference. Voltage references are used where you need a very stable voltage, such as the reference for an accurate A/D converter.
 
So a TL431 is parallel regulator (a 'shunt' regulator) not a series Regulator?

What is the difference between a series regulator and a parallel regulator?
 
The shunt regulator shorts out (shunts) the excess voltage to ground to keep the voltage constant. The series regulator is in series with the voltage and turns on more or less to keep it's output voltage constant.
 
Technically a shunt regulator normally works with a resistor in series with the power supply and shunts excess current to ground to control the voltage, This is similar to how a zener diode is typically used to regulate voltage.
 
A good example of what you can do with a TL431 can be found in post 11 of this thread.

In particular, see how much simpler Mike's TL431 based circuit is compared to the OPs original design.
 
Have you asked the designers at your work why they did it that way?

I've used the TL431 as a voltage reference for an A/D converter. Works like a charm.
 
Not don't know how Mike's TL431 circuit works and how he used it, do you know? what does it do

Look at the attached functional block diagram which comes directly from the TL431 data sheet. Note how the device works. It has an opamp with the inverting input tied to the internal voltage reference, which is 2.495V. The non-inverting input is the REF pin. The output of the opamp drives the base of the NPN transistor whose collector is the CATHODE pin, and whose emitter is the ANODE pin.

REF has a very high input impedance. The opamp amplifies the difference between V(REF) and 2.49V. The open loop gain of the opamp and NPN is greater than -1400, so only 1mV of difference causes the CATHODE pin to change by -1.4V.

The TL431 can be used as an audio "amplifier". It can also be used as a comparator, where the voltage at the REF pin is compared to 2.495V, and V(CATHODE) is low if V(REF)>2.495V or is high if V(REF)<2.495V. That is the mode I am using it....

Or it can be connected as a programmable Zener, or used directly as a 2.495V reference.
 

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