Programmable Voltage Reference TL431IZT , what does it do?

[Billy Mayo]

Why not use a zener diode or a resistor voltage divider as a voltage reference?

 

[MikeMl]

Why not use a zener diode or a resistor voltage divider as a voltage reference?

The accuracy of a Zener is usually no better than Vz +-10%, while the TL431 is 2.495V +- 0.055V, which is +-2.2%.

The dynamic impedance of a TL431 is about a factor of 1000 better than a Zener.

The TL431 can be trimmed with external resistors to get a specific desired voltage.

The voltage output of a voltage divider is no better regulated than whatever is feeding the top end of the voltage divider, so is not really a "voltage reference" at all.

 

[ChrisP58]

Why not use a zener diode or a resistor voltage divider as a voltage reference?

You seem to be stuck in this rut. As long as you refuse to see the extra capability that comes with the additional functionality, you won't see the power of the part.

While it can emulate a zener (with more precision and lower wasted power) it's big advantage comes when you separate the voltage ref input and the control output. You can do so much more than you could with a simple zener. Just be willing to open your eyes and try to learn something new.

 

[Billy Mayo]

when you separate the voltage ref input and the control output.

And what can you do when you do this?

 

[MikeMl]

And what can you do when you do this?

Billy,

you take information that members here take time to explain to you, then just ask the same question over and over, with no indication that you even read the posted material. Are you a Troll?

 

[tvtech]

OMG, you guys that have given all here have the patience of Job (from the Bible).

There are none worse though than those that refuse to learn....because you are not telling them what they want to hear/see.

Smacks of real stupidity instead of a Troll. Heck, I deal with this kind of stuff daily in the workplace. That is why my mind is as messed up as it is.
Please see this link here: https://en.wikipedia.org/wiki/Dunning–Kruger_effect

Regards,
tvtech

 

[tvtech]

Having another look at this thread...I think Billy Mayo is playing games here and wasting everyone's time and energy.

Work is hard enough. Not this too.

Regards,
tvtech

 

[Billy Mayo]

That is not true at all

 

[tvtech]

That is not true at all

Hello Billy

What is not true at all ?

tvtech

 

[ChrisP58]

That is not true at all

It probably isn't true, but it kind of looked that way.

You were given good reasons why the tl431 is better than a generic zener, as well as applications where a zener would require extra circuitry to compete, yet you kept asking the same question.

It just seemed like, instead of listening to and trying to learn from the answers, that you were just choosing to not understand.

 

[crutschow]

Perhaps he just doesn't want the thread to stop.

 

[tvtech]

Perhaps he just doesn't want the thread to stop.

Could be true...

Thing is, there are so many youngsters out there that listen at least....and then learn from our mistakes. Fezder is one. Has his own Blog here too..If he needs help, I will try my best

I like people like that. Not those that insist of knowing everything...and then don't listen anyway to good advise given

I don't have kids. Thank God. Or, maybe if I did, I would look at things differently . Nah, always me. Accuracy always.

Enough now

tvtech

 

[Billy Mayo]

It sounds like it keeps a REF at 2.4 volts and it compares it will the VCC +5 volts , it's a comparator with a REF at fixed 2.4 volts as a Reference compared to the external resistor

 

[ChrisP58]

It sounds like it keeps a REF at 2.4 volts and it compares it will the VCC +5 volts , it's a comparator with a REF at fixed 2.4 volts as a Reference compared to the external resistor

Not quite. The TL431 doesn't do anything to the REF pin. You can drive the REF pin to any voltage within the range of the part. The TL431 looks at the voltage on the REF pin and makes a decision that shows up on the cathode pin. Many, but not all, applications will close the loop through other circuitry that will cause the REF pin to be at 2.5V, but that is the external circuitry doing what the engineer designed it to do.

Look carefully at the block diagram for the TL431. You will see an internal voltage reference component (a 2.5V zener) connected to one input of a voltage comparator. The REF pin is connected to the other input. The comparator output drives a transistor whose collector pin is the output of the TL431.

 

[Billy Mayo]

So a TL431 is a comparator?

 

[MikeMl]

As I told you several posts ago, it contains an opamp.

Any opamp could be used as a comparator, or it can be used as an amplifier. In the 431, the opamp amplifies the expression (Vref-2.495) by -40,000 or so.

 

[Billy Mayo]

So it amplifies the REF signal voltage for what reason? is it amplifying the REF voltage for? It's amplifying the REF 2.4 volts for what reason?

 

[MikeMl]

Read it again:
the opamp amplifies the expression (Vref-2.495) by -40,000 or so

 

[ChrisP58]

Op-amps and comparators are very similar. In some cases you can use them interchangeably. I tend to think of the TL431 as containing a comparator due to it's open collector output. The block diagram does show it as an op-amp driving a transistor. I apologize for any confusion that I gave by calling it a comparator.

In the case of the TL431, it doesn't amplify the reference voltage. It amplifies the error between the internal reference voltage and the voltage at the REF pin.

Maybe a non-electrical example might help you to understand it.

Consider you are driving you car down the road. Your mind wants to go at 60 miles per hour (or whatever the unit of distance is where you are). This represents the internal reference voltage (2.5V). The speedometer of the car says you are doing 70MPH (the voltage at the REF pin is greater than 2.5V). Your brain (the comparator) sees that the car is going too fast, so it tells your foot (the cathode pin) to let up, sending less gas to the engine. If the car is going to slow, the same process will result in more gas being sent to the engine. If you are going at the speed you want, it will make no change in the gas feed. But as soon as external changes affect the speed (going up a hill) an error is detected, and the gas feed is changed.

This is how the TL431 is usually used in a power supply. It looks at a sample of the output voltage (via a resistor divider feeding the REF pin) and decides if the power supply engine needs to work harder, less hard, or stay the same, in order for the voltage to be what it is supposed to be. This error signal is communicated to the power supply controller by a change in current drawn by the cathode pin of the TL431.

 

[tvtech]

Op-amps and comparators are very similar. In some cases you can use them interchangeably. I tend to think of the TL431 as containing a comparator due to it's open collector output. The block diagram does show it as an op-amp driving a transistor. I apologize for any confusion that I gave by calling it a comparator.

In the case of the TL431, it doesn't amplify the reference voltage. It amplifies the error between the internal reference voltage and the voltage at the REF pin.

Maybe a non-electrical example might help you to understand it.

Consider you are driving you car down the road. Your mind wants to go at 60 miles per hour (or whatever the unit of distance is where you are). This represents the internal reference voltage (2.5V). The speedometer of the car says you are doing 70MPH (the voltage at the REF pin is greater than 2.5V). Your brain (the comparator) sees that the car is going too fast, so it tells your foot (the cathode pin) to let up, sending less gas to the engine. If the car is going to slow, the same process will result in more gas being sent to the engine. If you are going at the speed you want, it will make no change in the gas feed. But as soon as external changes affect the speed (going up a hill) an error is detected, and the gas feed is changed.

This is how the TL431 is usually used in a power supply. It looks at a sample of the output voltage (via a resistor divider feeding the REF pin) and decides if the power supply engine needs to work harder, less hard, or stay the same, in order for the voltage to be what it is supposed to be. This error signal is communicated to the power supply controller by a change in current drawn by the cathode pin of the TL431.

Excellent analogy Chris. Explains it in very basic terms +1.

Regards,
tvtech