Calculation of original value in TL431 sampling compensation-EEWORLD

Collect

As a controllable precision voltage regulator, TL431 has the characteristics of low price and high performance, so it is widely used in various electronic circuits. This article will introduce the calculation of the original value in TL43 sampling compensation.

Take the following circuit diagram as an example, where the value of R6 is not randomly determined. The parameters of R6 mainly depend on two factors: the first is the current at the reference input end of TL431, which is generally about 2uA. In order to avoid the current at this end affecting the voltage divider ratio and avoid the influence of noise, the current flowing through resistor R6 is generally taken to be more than 100 times the reference current, so this resistance should be less than 2.5V/200uA=12.5K. The second is the requirement for standby power consumption. If there is such a requirement, try to take a larger value while meeting <12.5K.

Those who are familiar with power supply design must know that TL431 requires 1mA of operating current, which means that when the current of R1 is close to zero, TL431 must also be guaranteed to have 1mA, so R3≤1.2V/1mA=1.2K. On the other hand, it is also for power consumption considerations.

Therefore, for the design of the circuit, the value of R1 is very important, it must ensure that the TOP control terminal can get enough current. Assuming PC817A is used, its CTR = 1.6-0.8, take the lower limit 0.8, the maximum current flowing through the photodiode is required to be 6/0.8 = 7.5mA, so the value of R1 is ≤ (15-2.5-1.2)/7.5 = 1.5K, the maximum current that the photodiode can withstand is about 50mA, and TL431 is 100mA, so the maximum current flowing through R1 is 50mA, R1> (15-2.5-1.3)/50 = 226 ohms.

In the above figure, we can see that R5 and C4 form a pole at the origin, which is used to improve the low-frequency gain to suppress the low-frequency (100Hz) ripple and improve the output regulation rate, that is, the static error. R4C4 forms a zero point to improve the phase, which should be placed in front of the bandwidth frequency to increase the phase margin. The specific position depends on the phase of the remaining power part at the design bandwidth. The lower the frequency of R4C4, the higher the phase it improves. Of course, the maximum is only 90 degrees, but when the frequency is very low, the low-frequency gain will also decrease. It is generally placed at the beginning of 1/5 of the bandwidth, which improves the phase by about 78 degrees.

So far, this is the complete calculation method of the original value in the sampling compensation of TL431. In addition, this method is applicable to any primary IC. Interested friends can replace it with another model of IC to perform calculations.

Keywords：TL431 Reference address：Calculation of original value in TL431 sampling compensation

Previous article：Knowing the division of labor of each pin of TL494 will definitely not be difficult for you in practical application
Next article：The internal structure and application of RCC

Recommended ReadingLatest update time:2024-11-22 13:36

Using the TL431 Shunt Regulator to Limit High AC Input Voltage

In an SMPS, the circuit clamps the input AC voltage to a safe level at which the power MOSFET operates. 　　Most isolated, offline SMPS (switching power supplies), including flyback, forward and resonant, must operate at an input voltage of 90 to 260 V RMS. Some cases even use a line voltage of 400 V RMS ±10%, resulti

[Analog Electronics]

Using the TL431 Shunt Regulator to Limit High AC Input Voltage

Popular Resources
Popular amplifiers