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How is the TL431 used in power supplies?
Original photo by Zeptobars . The TL431 is a “programmable precision reference” [1] and is commonly used in switching power supplies, where it provides feedback indicating if the output voltage is too high or too low. By using a special circuit called a bandgap, the TL431 provides a stable voltage reference across a wide temperature range.
Why are resistors on the TL431 so poor?
Resistors in the TL431. Resistors in ICs have very poor tolerance – the resistance can vary 20% from chip to chip due to variations in the manufacturing process. This is obviously a problem for a precision chip like the TL431.
What does the sinking end of TL431 do?
The sinking end of TL431 drives the light-emitting part of an optocoupler. The feedback voltage obtained by the photosensitive part of the photocoupler on the main side of the power supply is used to adjust the switching time of a current mode PWM controller.
What are the transfer characteristics of the TL431 circuit?
TL431 Circuit: Comparator As shown in the figure, use the transfer characteristics of TL431 to form a practical voltage monitor. When the voltage is between the upper and lower limit voltages, the LED power and upper and lower limit voltages are (1+R1/R2)Vref and (1+R3/R4)Vref respectively.
The TL431 is a “Programmable Precision Reference” and is commonly used in switching power supplies, where it provides feedback indicating if the output voltage is too high or too low. By using a special circuit called a bandgap, the TL431 provides a stable voltage reference across a wide temperature range.
When does the TL431 trigger the V protection point?
As shown in the figure, when Vi exceeds a certain voltage, TL431 triggers. At this time, the thyristor is turned on and generates a large instantaneous current, which blows the fuse, thereby protecting the rear circuit. V protection point = (1+R1/R2)Vref. Figure 3. TL431 Circuit: Overvoltage Protection As the picture shows.
What are the voltages of the TL431 shunt regulator?
When the voltage is between the upper and lower limit voltages, the LED power and upper and lower limit voltages are (1+R1/R2)Vref and (1+R3/R4)Vref respectively. It can be seen from the functional module diagram of TL431 that when the voltage at the REF terminal changes slightly, the shunt from the cathode to the anode will change within 1-100mA.
What should the filtering capacitor be for TL431?
C6 is the main filtering capacitor, which should be at least 2200µF. Voltage produced by TL431 is adjusted with potentiometers VRx (VR1 through VR6) and can be calculated with the simplified formula given below:
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