Wiring diagram and characteristics TL 431
Performance, ease of connection to most circuits and excellent performance have made the TL 431 a very popular regulated regulator on the market.
With a small set of additional electronic components (several capacitors and resistors), it can provide an operating voltage of 2.5 to 36 V, with a stabilization current of 1 to 100 mA. In order to get large values at the output of the microcircuit, high power transistors are usually added. Such an element is also called a controlled programmable zener diode.
It was first introduced to the world in 1977.
Since that time, it has been constantly improved and has now become an integral part of most modern switching-type power supplies, where they play the role of a reference voltage source. It can be an excellent replacement for Zener diodes in various electronic type circuits. Let's consider the connection diagram of TL 431.
The pinout of the stabilizer will depend on the case version of the device in which it will be placed.
There are only five varieties:
- For mounting in holes - TO-92.
- For Surface Mount - SOT-8, SOT-22, SOT-25, and SOP-89.
For electronic type circuits, there are only three contacts inside these plastic packages, the first being the control electrode, the second anode and the third cathode. There are more metal leads in certain types of cases of such a microcircuit, and at the same time they are not used or are combined with neighboring ones. How this is done is shown in the photo.
We suggest considering the maximum permissible operating properties of the microcircuit. If, during its application, they are exceeded, then the device will inevitably fail. Long-term operation with characteristics that are close to the limit value is also unacceptable. Let's consider them in more detail:
5W (SOT-25); 0.8 W (SOT-89) and 0.78 W (TO-92).
The maximum power dissipation can be calculated using the usual formula P D = (T Jmax -T A ) / R θJC . In this case, T A is the temperature in the environment.
Recommended operating parameters
Under operating conditions, the recommended values for the use of the stabilizer is an input voltage of the reference type no more than 36 V, the cathode current must be from 1 to 100 mA, as well as compliance with temperature conditions during application. It should be noted that with I KA . 5mA, this microcircuit may be unstable.
Below there are electrical parameters of the device, which were measured at a temperature level of T A = 25 degrees.
It is required to understand how the element works on the example of a simple stabilization circuit, which consists directly of a zener diode and 1 resistor. It is required to connect the positive pole to the cathode, and the negative pole to the anode for power supply. To connect the microcircuit, a reference voltage must be applied to its control electrode. If the value of the TL stabilizer turns out to be more than 2.
5 V, then the Zener diode will open almost immediately and begin to pass an electric current through itself, which can be used to supply the required load. Its value will begin to grow along with an increase in the V in level. But the current can be determined by the formula I KA = (V in - V ref ) / R. In this case, the voltage of the output type will be stabilized at the reference level, which is not more than 2.5 V and regardless of the V in supplied at the input.
The maximum value of I KA of the stabilizer is limited not only by 100 mA, but also by the power of the case dissipation.
Calculation of the parametric stabilization circuit
In order to receive a larger voltage at the output of the microcircuit (up to 36 V), k its control-type cathode additionally requires a resistive divider to be connected. It is made of two resistors that are connected between the anode and cathode. In this case, the internal resistance of the zener diode increases. To calculate the stabilization circuit, initial data on the output and input voltages, and also currents - load and stabilization are required.
Having this data, you can calculate the values of the remaining electronic components, which are presented in the diagram below. The output voltage, as well as the resistance ratings are related to each other by the following formula - V KA = V ref * (1 + R 1 / R 2 ) + Ir ef * R 1 . In this case, V ref = 2495 mV and I ref = 2 μA are typical values, and they are written in the electrical parameters on the device. The resistance of the first resistor can be taken from the datasheet. Usually they are taken with a nominal value of 10-30 kΩ, and the value of the first resistor is limited to a small reference current (2 μA), and it is often neglected for calculating stabilization circuits.
For this reason, to calculate the value of the second resistor, another formula can be used R 2 = R 1 / ((V KA / V ref ) -1).
Regulation of stabilization voltage
To build circuits with the ability to manually adjust the output voltage, a potentiometer is installed instead of a simple first resistor. The value of the limiting resistor, which provides resistance to the current at the input, must be calculated using the formula R = (V IN -VK A ) / I IN . In this case, I IN = I KA + I L . Despite the advantages of the microcircuit, it has a rather significant disadvantage - a small current in the load, which it can withstand.
To solve this problem, you need to connect field-effect or powerful bipolar transistors to the circuit. Examples of different schemes can be seen in the video.
There are domestically produced microcircuits that are similar in their properties to the one under consideration. This is the linear Russian stabilizer KR142EN19. The IR943N, TL432 and LM431 are most suitable.
HA17431A and KIA431 can be attributed to devices with such a pinout, but with slightly different other electrical characteristics. In the role of a replacement, you can still try to use the APL1431.
This microcircuit cannot be tested with a multimeter, because it is not just a zener diode, but a whole integrated circuit. The resistances between its leads differ from manufacturer to manufacturer. For this reason, to make sure that it is in good condition, as a rule, simple test schemes are assembled.
In order to check in the image circuit, 12 V is supplied to the input. If the device is in good working order, then the output should have a voltage of 4-9 to 5 V, and if there is a short circuit S 1 - 2.5 V. , in such a case, is required to measure the test results.
You can also check the circuit by another test with an LED, and when the resistance of the second resistor of the potentiometer changes, 2.
5 V will appear on the control electrode. The diode should jump into a state of light. This will mean that the device is working properly. This principle can be applied in order to create a battery discharge indicator.
( 7 marks, average 1.
86 of 5 )
Posted By: Work Style |03, Nov 2020
Posted By: Work Style |06, Nov 2020
Posted By: Work Style |04, Nov 2020
Posted By: Work Style |04, Nov 2020
Posted By: Work Style |06, Nov 2020