In 1977, Texas Instruments introduced the TL431 Zener diode, which works similarly to a Zener diode. It is a three-terminal bipolar transistor, equivalent to an ideal N-type transistor without hysteresis losses.
In addition, TL431 is a shunt voltage regulator, which means it can regulate voltage. Its equivalent series models are ATL431, TL432, LM431, KS431, TS431 and 142EH19 voltage regulators. These regulator circuits are functionally similar and differ only in their size, accuracy, layout, operating current, and speed characteristics. In this article, the editor will briefly introduce the working principle, specifications and application circuit of the TL431 voltage regulator.
TL431 Basic concept
The TL431 voltage regulator is an adjustable precision shunt regulator IC that can program the output voltage by changing the value of the connected resistor. Therefore, it is called a programmable shunt regulator. The working principle of the TL431 is almost similar to that of a Zener diode, except that the voltage rating is programmable.
TL431 is also known as an adjustable Zener diode and is mainly used in circuits to provide a positive voltage reference or a negative voltage reference. It is low cost and is often used as a reference voltage provider in isolated power circuits. Its symbol is shown in the figure below:
Figure 1: TL431 voltage regulator and three-terminal pin
TL431 is a three-terminal parallel zener diode integrated circuit, using TO-92 package type. The resistor divider connected to the TL431 reference terminal is adjusted to change the output voltage rating from 2.5 volts to 36 volts. The operating current range is 1mA to 100mA and the typical impedance value is 0.22 ohms.
The TL431 provides stable performance over a wide operating temperature range. And it can also be used when the Zener diode needs to be replaced in various applications because its working principle is almost similar to the Zener diode except that the output voltage is programmable and adjustable. It is widely used in overvoltage and undervoltage monitoring circuits, window voltage monitoring circuits, power supplies as reference voltage sources, etc.
TL431 Pin configuration
The TL431 is a 3-terminal shunt regulator with certain thermal stability over applicable automotive, military and commercial temperature ranges. Its pin configuration is as follows:
Figure 2: TL431 three-terminal pin configuration information diagram
Pin1 (Reference): used to set the rated voltage of the Zener diode.
Pin2 (Anode): It is the anode terminal of the equivalent Zener diode.
Pin3 (Cathode): It is the cathode terminal of the equivalent Zener diode.
Specifications
The specifications of the TL431 voltage regulator are as follows:
It's also a zener diode, programmable.
The output voltage range is from 2.5 volts to 36 volts.
The output voltage tolerance is +-4%.
Output or sink current ranges from 1mA to 100mA.
The output impedance is 0.22 ohms.
The 3-pin TL431 is available in TO-92 package type, and the 8-pin TL431 is available in SOIC and PDIP packages.
The operating temperature range is -40°C to 125°C.
The output noise is low.
Typical temperature drift: 6mV (Ctemp) and 14mV (ITemp, Qtemp).
At 25°C, reference voltage tolerances are 1% (Grade A), 0.5% (Grade B), and 2% (Standard Grade).
The cost is very low.
How to test TL431
As shown in the figure is the circuit tested by TL431. The power supply is 0~20V maintenance power supply. An ammeter is connected between the K pole and the power supply to clearly observe the changes in the K pole current caused by changes in the G pole voltage. By connecting a voltmeter between K and A, you can clearly observe the changes in the output terminal of TL431 as the power supply changes. Before testing, adjust the potentiometer to near the middle value. Use Shengli 89B digital meter to measure the voltage of K pole to ground, adjust the voltage output of the maintenance power supply, and find that the voltage of K pole to ground has only two states, one is about 2V (low level); the other is equal to the power supply voltage (high level) level).
TL431 tested circuit
Judgment of normality or not. For the online TL431 power supply error comparator, an external maintenance power supply can be used for testing. Connect the maintenance power supply to the sampling point of TL431. When the voltage is adjusted to be higher than the nominal voltage, TLA31 will be turned on and the K pole voltage will be low level. That is to say, when the power supply voltage rises, TL431 turns on, allowing the diode of the photocoupler to turn on, making the transistor in a saturated state. Finally, the conduction time of the primary power switch tube is shortened (the duty cycle is reduced), so that the output Voltage drops. If the maintenance voltage is lowered, TL431 will be cut off, the K-pole voltage will be at a high level, and the diode of the photoelectric coupler will be cut off, making the triode in a cut-off state, ultimately controlling the conduction time of the primary power switch tube of the transformer to increase (increasing the duty cycle). ratio). Increase the output voltage. The closed-loop voltage stabilizing circuit of the switching power supply uses the two states of TL431 to adjust the duty cycle of the switching tube to control the stability of the output voltage. When measuring with a multimeter, if the resistance between the IC poles is normal, it can be judged that the TL431 is normal: when using the maintenance power supply to power up the test. When the power supply voltage is changed, if the TL431 pole has two levels of high and low changes to the ground, It can be judged that TL431 is normal.
Application Circuit
1. Regulator integrated circuit
The circuit diagram using the TL431 voltage regulator integrated circuit is shown below:
TL431 voltage regulator integrated circuit diagram
In the above circuit diagram, it can be observed that the NPN transistor is biased from the op-amp with a precise reference voltage rating of 2.5 volts on the non-inverting terminal. The collector terminal of the transistor is connected to the cathode terminal of the TL4311C, and the emitter terminal of the transistor is connected to the anode terminal of the TL431IC.
Now consider the TL431 voltage regulator used as a comparator, one side of the comparator will have an exact voltage of 2.5 volts and the other side is set with the help of the reference terminal. This feature is mainly suitable for SMPS (Switch Mode Power Supply) because the TL431 regulator can compare the obtained output voltage with the desired output voltage and control the switching frequency by providing a feedback path. To isolate the high voltage section, optical couplers are often used with this circuit setup.
2. Precision reference voltage circuit
The circuit diagram of precision reference voltage circuit using TL431 voltage regulator is shown below, which provides better temperature stability and huge output current. To avoid self-excitation, the value of CL should be carefully considered when connecting capacitive loads.
Precision reference voltage circuit diagram of TL431 regulator
3. Adjustable regulated power supply
The adjustable range of the output voltage Vo is between 2.6 volts and 36 volts, and the expression of the output voltage Vo is written as:
Vo=Vref(1+R1/R2)
Because Vref is set to 2.5 volts, the voltage the circuit can withstand is related to (Vo-Vi). If there is a large voltage difference, the power dissipated by the resistor increases. The circuit diagram of an adjustable regulated power supply using a TL431 Zener diode is shown below:
Circuit diagram of adjustable regulated power supply using TL431 Zener diode
4. Voltage comparator
In this application, the voltage Vref=2.5 Volts is effectively used. The small internal resistance in the TL431 Zener diode helps to track the input and output waveforms very easily and efficiently. The circuit diagram of the voltage comparator using TL431 Zener diode is shown in the figure below:
Voltage comparator circuit diagram using TL431 Zener diode
5. Voltage monitor
The transfer characteristics of a voltage regulator are used to actually design a voltage monitor. At the upper and lower limit voltages, the LED power, upper and lower limit voltages will be (1+R1/R2) and (1+R3/R4) respectively. The circuit diagram below illustrates a voltage monitor using a TL431 Zener diode:
Voltage monitor using TL431 Zener diode
6. Overvoltage protection circuit
When the input voltage Vi exceeds a certain voltage, the regulator starts to trigger. At this time, the thyristor is turned on and generates a large instantaneous current. This helps blow the fuse and protects the rear circuit. At the protection point, the voltage will be (1+R1/R2)Vref. The circuit diagram of using TL431 for overvoltage protection is as follows:
Circuit diagram for overvoltage protection using TL431
Main application
The following is a brief list of some applications of the TL431 voltage regulator:
For SMPS (switched mode power supply)
Used in isolated power circuits
For voltage comparators with integrated reference
Used in current regulation circuits
For use in precision voltage reference circuits
For overvoltage protection circuits
For voltage monitor
For constant current source circuit
For controlled shunt characteristics
Can be used when the Zener diode needs to be replaced
Used in monitor and battery charger circuits
Alternatives to the TL431 regulator are Zener diodes and variations of the TLV431, LM431 and TS431L1 regulators.
Summarize
The above is the relevant content about the TL431 voltage regulator data sheet, including specifications, pin configuration/pin diagram, application circuit, etc. In fact, through the introduction of the above content, we can see that the TL431 voltage regulator has many advantages. It is basically equivalent to a Zener diode, and the voltage can still be adjusted.
Nantian Electronics a professional distributor of electronic components, providing a wide range of electronic products, saving you a lot of time, effort and cost through our meticulous order preparation and fast delivery service.
Share this post
