Several basic uses of tl431-2.5v voltage reference chip

TL431 Of internal structure :
TL431 The specific functions of can be illustrated by the function modules in the figure below . You can see from the picture that ,VI It's an internal 2.5V The benchmark of , Connected to the reverse input of the operational amplifier . From the characteristics of operational amplifier , Only when REF End （ In the same direction ） The voltage of is higher than VI（2.5V） when , There will be current in the triode , In phase input voltage is less than 2.5V when , The triode is off （ ideally ）, With REF Small changes in terminal voltage , Through the triode diagram 1 The current will flow from 1mA To 100mA change . Of course , The picture is by no means TL431 The actual internal structure of , But it can be used to analyze and understand circuits .
TL431 The internal equivalent circuit is shown in the figure .


 

TL431 As a common shunt voltage reference with high cost performance , It has a wide range of uses . Here is a brief introduction TL431 Common and uncommon connections .
 

chart (1) yes TL431 Typical connection of , Output a fixed voltage value , The formula is ： Vout = (R1+R2)*2.5/R2,

meanwhile R3 The value of should meet 1mA < (Vcc-Vout)/R3 < 500mA

When R1 The value is 0 When ,R2 It can be omitted , At this time, the circuit becomes a diagram (2) In the form of ,TL431 It is equivalent to a 2.5V Regulator tube .

utilize TL431 It can also form an amplitude discriminator , Pictured (3), This circuit is at the input voltage Vin < (R1+R2)*2.5/R2 When output Vout High level , On the contrary, the output is close to 2V The level of . The thing to notice is when Vin stay (R1+R2)*2.5/R2 When it fluctuates in small amplitude nearby , The circuit will output unstable values .

TL431 It can be used to raise a near ground voltage , And invert it . Pictured (4), The output calculation formula is ： Vout = ( (R1+R2)*2.5 - R1*Vin )/R2

Special , When R1 = R2 When ,Vout = 5 - Vin. This circuit can be used to raise a voltage close to ground to a preset range , The only thing to notice is that TL431 The output range of is not full .

TL431 It has quite high gain （ I test roughly in the simulation , Presumably 46db）, So it can be used as an amplifier .

chart (5) Shows a with TL431 Composed of DC voltage amplifier , The magnification of this circuit is determined by R1 and Rin decision , Equivalent to the negative feedback loop of the operational amplifier , Its static output voltage is determined by R1 and R2 decision .

The advantage of this circuit is , It has a simple structure , The accuracy is also good , It can provide stable static characteristics . The disadvantage is that the input impedance is small ,Vout The swing of is limited .

chart (6) It's an AC amplifier , This structure is very similar to DC amplifier , And it has the same advantages and disadvantages . I'm trying to use this amplifier instead of the secondary op amp to amplify the output signal of the thermoluminescence infrared sensor .