The integrated stabilizer TL431 is usually used in power supplies. But you can still choose many areas of use for it. We will describe some of these schemes in this article, and also talk about useful and simple devices, made using the TL431 chip. But in this case, there is no need to be intimidated by the term “microcircuit”; it has only three outputs, and in appearance it is similar to a simple low-power transistor TO90.

What is the TL431 chip?

It just so happens that all electronics engineers know the magic numbers TL431, analogous to 494. What is it?

Texas Instrument Company was at the origins of semiconductor development. They have always been in first place in the production of electronic components, constantly remaining in the top ten world leaders. The first integrated circuit was developed back in 1958 by an employee of this company, Jack Kilby.

Today, TI produces a large range of microcircuits, their names begin with the letters SN and TL. These are, respectively, logical and analog microcircuits that have forever entered the history of the TI enterprise and are still widely used.

Among the favorites in the list of “magic” microcircuits you should most likely include an integrated stabilizer TL431. There are 10 transistors installed in the 3-output package of this microcircuit, and the function it performs is identical to a simple zener diode (Zenner diode).

But thanks to this complication, the microcircuit has an increased steepness of characteristics and higher thermal stability. Its main feature is that with the help of an external divider the stabilization voltage can be changed in the range of 2.6…32 Volts. In modern TL431, the analogue of the lower threshold has 1.25 Volts.

The TL431 analogue was developed by engineer Barney Holland when he was copying a stabilizer circuit from another company. In our country they would say ripping, not copying. And Holland borrowed a reference voltage source from the original circuit, and on this basis developed a separate stabilizer chip. At first it was called TL430, and after certain modifications it became known as TL431.

A lot of time has passed since then, but today there is not a single power supply for a computer where it is not installed. The circuit has also found application in almost all switching low-power power supplies. One of these sources is present in any home today - it is a charger for mobile phones. One can only envy this longevity.

Holland also developed the no less famous and still in demand circuit TL494. This dual-frequency PWM controller, on the basis of which many types of power supplies are made. Therefore, the number 494 is also rightfully considered “magical”. But let's move on to looking at different products based on the TL431.

Alarms and indicators

The TL431 analog circuits can be used not only for their intended purpose as zener diodes in power supplies. Based on this microcircuit, it is possible to create various sound alarms and lighting indicators. These devices can be used to check many different parameters.

For starters, this normal voltage voltage. If some physical quantity is represented as voltage using sensors, then you can create equipment that controls, for example:

• humidity and temperature;
• water level in the tank;
• gas or liquid pressure;
• illumination

The operating principle of this alarm is based on the fact that when the voltage on the control electrode of the zener diode DA1 (output 1) is less than 2.6 Volts, the zener diode is closed, only a low current passes through it, usually no more than 0.20...0.30 mA. But this current is enough for the HL1 diode to glow weakly. To prevent this phenomenon from happening, you can connect a resistor with a resistance parallel to the diode approximately 1…2 KOhm.

If the voltage at the control electrode is more than 2.6 Volts, the zener diode will open and diode HL1 will light up. The required voltage limitation through the zener diode DA1 and diode HL1 is created by R3. The highest current of the zener diode is 100 mA, while the HL1 diode has the same parameter only 22 mA. It is from this condition that the resistance of resistor R3 can be calculated. More precisely, the resistance is calculated using the formula below.

R3=(Upit – Uhl - Uda) / Ihl, where:

• Uda – current on an open chip (usually 2 Volts);
• Uhl – direct current drop across the diode;
• Upit – supply current;
• Ihl – diode voltage (in the range 4...12 mA).

You also need to remember that the highest voltage for the TL431 is only 36 Volts. This parameter must not be exceeded.

Alarm level

The current at the control electrode when the diode HL1 (Uз) turns on is set by the separator R1, R2. The characteristics of the separator are determined by the formula:

R2=2.5хR1/(Uз – 2.5)

To adjust the switching threshold as accurately as possible, instead of resistor R2, you can install a trimmer, with an indicator 1.5 times higher than what was calculated. Then, when the tuning is done, it can be replaced with a constant resistor, its resistance should be equal to the resistance of the installed part of the trimmer.

How to check TL431 switching circuit? To monitor several current levels, 3 of these alarms will be needed, each of them is adjusted to a specific voltage. In this way you can make a whole line of scales and indicators.

To power the indication circuit, which consists of resistor R3 and diode HL1, you can use a separate, even unstabilized, power source. In this case, the controlled current is supplied to the upper output of resistor R1 in the circuit, which must be disconnected from resistor R3. With this connection, the controlled current can be in the range from 3 to tens of volts.

The difference between this circuit and the previous one is that the diode is connected differently. This connection is called inverse, since the diode turns on only if the circuit is closed. In the case when the controlled current exceeds the threshold specified by the separator R1, R2, the circuit is open, and the current passes through resistor R3 and outputs 3 - 2 of the microcircuit.

In the diagram, in this case, the voltage drops to 2 Volts, which is not enough to turn on the LED. To ensure that the diode does not turn on, two diodes are installed in series with it.

If the controlled current is less than that set by the separator R1, the R2 circuit will close, the current at its output will be significantly greater than 2 Volts, because diode HL1 will turn on.

If you only need to monitor the change in current, then the indicator can be made according to the diagram.

This indicator uses a 2-color HL1 diode. If the monitored current exceeds the set value, the red diode turns on, and if the current is lower, then the green diode turns on. If the voltage is located near this threshold, both LEDs are extinguished, because the transfer position of the zener diode has a certain slope.

If you need to track a change in some physical quantity, then R2 is replaced with a sensor that changes the resistance under the influence environment.

Conventionally, the diagram contains several sensors simultaneously. If it is a phototransistor, then there will be a photo relay. As long as there is enough light, the phototransistor is open and its resistance is low. Therefore, the current at the control output DA1 below threshold, as a result of this the diode does not light up.

As the light decreases, the resistance of the phototransistor increases, this leads to an increase in the voltage at the control output DA1. If this voltage is greater than the threshold (2.5 Volts), then the zener diode opens and the diode lights up.

If you connect a thermistor, instead of a phototransistor, to the input of a microcircuit, for example, the MMT series, then a temperature indicator will appear: when the temperature decreases, the diode will turn on.

In any case, the response threshold is set using resistor R1.

In addition to the described light indicators, an analogue can be made based on the TL431 sound indicator. To control water, for example, in a bath, a sensor made of two stainless steel plates, which are located at a distance of a couple of millimeters from each other, is connected to the circuit.

If water reaches the sensor, its resistance decreases, and the microcircuit, with the help of R1, R2, enters linear mode. So, autogeneration occurs at the resonant frequency NA1, in this case a beep will sound.

To summarize, I would like to say that the main area of ​​use of the TL434 chip is, of course, power supplies. But, as you can see, the capabilities of the microcircuit are absolutely not limited to this function alone, and many devices can be assembled.

Nikolay Petrushov

TL431, what kind of “beast” is this?

Rice. 1 TL431.

TL431 was created in the late 70s and is still widely used in industry and in amateur radio activities.
But despite its advanced age, not all radio amateurs are closely familiar with this wonderful case and its capabilities.
In this article I will try to familiarize radio amateurs with this microcircuit.

First, let's look at what's inside it and turn to the documentation for the microcircuit, the "datasheet" (by the way, analogs of this microcircuit are KA431, and our KR142EN19A, K1156ER5x microcircuits).
And inside it there are about a dozen transistors and only three outputs, so what is it?

Rice. 2 Device TL431.

It turns out everything is very simple. Inside is a conventional op-amp (triangle in the block diagram) with an output transistor and a reference voltage source.
Only here this circuit plays a slightly different role, namely the role of a zener diode. It is also called “Controlled Zener diode”.
How does it work?
Let's look at the TL431 block diagram in Figure 2. From the diagram you can see that the op-amp has a (very stable) built-in 2.5 volt reference voltage source (small square) connected to the inverse input, one direct input (R), a transistor at the op-amp output, a collector ( K) and an emitter (A), which are combined with the power supply terminals of the amplifier and a protective diode against polarity reversal. Maximum current the load of this transistor is up to 100 mA, the maximum voltage is up to 36 volts.

Rice. 3 Pinout TL431.

Now, using the example of a simple circuit shown in Figure 4, let’s look at how it all works.
We already know that inside the chip there is a built-in reference voltage source - 2.5 volts. In the first releases of microcircuits, which were called TL430, the voltage of the built-in source was 3 volts, in later releases it reaches 1.5 volts.
This means that in order for the output transistor to open, it is necessary to input (R) operational amplifier, apply a voltage slightly higher than the reference 2.5 volts (the prefix “slightly” can be omitted, since the difference is several millivolts and in the future we will assume that a voltage equal to the reference must be applied to the input), then a voltage will appear at the output of the operational amplifier and the output transistor will open.
To put it simply, TL431 is something like field effect transistor(or simply a transistor), which opens when a voltage of 2.5 volts (or more) is applied to its input. The opening-closing threshold of the output transistor is very stable here due to the presence of a built-in stable reference voltage source.

Rice. 4 Circuit diagram for TL431.

From the diagram (Fig. 4) it can be seen that a voltage divider consisting of resistors R2 and R3 is connected to the R input of the TL431 microcircuit, resistor R1 limits the LED current.
Since the divider resistors are the same (the power supply voltage is divided in half), the output transistor of the amplifier (TL-ki) will open when the power source voltage is 5 volts or more (5/2 = 2.5). In this case, 2.5 volts will be supplied to the R input from the divider R2-R3.
That is, our LED will light up (the output transistor will open) when the power source voltage is 5 volts or more. It will go out accordingly when the source voltage is less than 5 volts.
If you increase the resistance of resistor R3 in the divider arm, then it will be necessary to increase the voltage of the power supply to more than 5 volts, so that the voltage at the input R of the microcircuit supplied from the divider R2-R3 again reaches 2.5 volts and the output transistor TL opens -ki.

It turns out that if this voltage divider (R2-R3) is connected to the output of the power supply, and the cathode of the TL-ki to the base or gate of the control transistor of the power supply, then by changing the arms of the divider, for example by changing the value of R3, it will be possible to change the output voltage of this power supply, because at the same time, the TL stabilization voltage (opening voltage of the output transistor) will also change - that is, we will get a controlled zener diode.
Or if you select a divider without changing it in the future, you can make the output voltage of the power supply strictly fixed at a certain value.

Conclusion;- if the microcircuit is used as a zener diode (its main purpose), then by selecting the resistances of the divider R2-R3 we can make a zener diode with any stabilization voltage within the range of 2.5 - 36 volts (maximum limitation according to the “datasheet”).
A stabilization voltage of 2.5 volts is obtained without a divider if the input of the TL is connected to its cathode, that is, pins 1 and 3 are short-circuited.

Then more questions arise. Is it possible, for example, to replace the TL431 with a regular op-amp?
- It’s possible only if you want to design it, but you will need to assemble your own 2.5-volt reference voltage source and supply power to the op-amp separately from the output transistor, since its current consumption can open the actuator. In this case, you can make the reference voltage whatever you want (not necessarily 2.5 volts), then you will have to recalculate the resistance of the divider used in conjunction with the TL431, so that at a given output voltage of the power supply, the voltage supplied to the input of the microcircuit is equal to the reference.

One more question - is it possible to use the TL431 as a regular comparator and build on it, say, a thermostat, or something similar?

It is possible, but since it differs from a conventional comparator in the presence of a built-in reference voltage source, the circuit will be much simpler. For example this;

Rice. 5 Thermostat on TL431.

Here the thermistor (thermistor) is a temperature sensor, and it decreases its resistance as the temperature increases, i.e. has a negative TCR (Temperature Coefficient of Resistance). Thermistors with positive TCS, i.e. The resistance of which increases with increasing temperature is called posistors.
In this thermostat, when the temperature exceeds a set level (regulated by a variable resistor), a relay or some actuator will operate and switch off the load (heating elements) with its contacts, or, for example, turn on the fans depending on the task.
This circuit has a small hysteresis, and to increase it, it is necessary to introduce an OOS between pins 1-3, for example, a trimming resistor of 1.0 - 0.5 mOhm and its value must be selected experimentally depending on the required hysteresis.
If it is necessary for the actuator to operate when the temperature drops, then the sensor and regulators must be swapped, that is, the thermistor must be included in the upper arm, and a variable resistance with a resistor must be switched on in the lower arm.
And in conclusion, you can easily understand how the TL431 microcircuit works in the circuit of a powerful power supply for a transceiver, which is shown in Figure 6, and what role resistors R8 and R9 play here, and how they are selected.

Rice. 6 Powerful block power supply 13 volts, 22 amperes.

TL 431 is a programmable shunt voltage regulator. Although this integrated circuit began to be produced in the late 70s, it still does not lose its position in the market and is popular among radio amateurs and large manufacturers electrical equipment. The board of this programmable stabilizer contains a photoresistor, a resistance measurement sensor and a thermistor. TL 431 are widely used in a wide variety of electrical appliances, household and industrial equipment. Most often, this integrated zener diode can be found in power supplies for computers, televisions, printers and chargers for lithium-ion batteries phones.

TL 431 integrated zener diode

Key Features of the TL 431 Programmable Voltage Reference

• ​ Rated operating voltage at the output is from 2.5 to 36 V;
• Output current up to 100 mA;
• Power 0.2 Watt;
• Range operating temperature for TL 431C from 0° to 70°;
• The operating temperature range for TL 431A is from -40° to +85°.

The accuracy of the TL 431 integrated circuit is indicated by the sixth letter in the designation:

• Accuracy without a letter – 2%;
• Letter A – 1%;
• Letter B – 0.5%.

Its widespread use is due to its low price, universal form factor, reliability, and good resistance to aggressive factors. external environment. But it should also be noted the accuracy of this voltage regulator. This allowed him to occupy a niche in microelectronics devices.

The main purpose of the TL 431 is to stabilize the reference voltage in the circuit. Provided that the voltage at the source input is below the rated reference voltage, the transistor in the programmable module will be closed and the current passing between the cathode and anode will not exceed 1 mA. If the output voltage exceeds the programmed level, the transistor will open and electric current will be able to pass freely from the cathode to the anode.

Wiring diagram TL 431

Depending on the operating voltage of the device, the connection circuit will consist of a single-stage converter and expander (for 2.48 V devices) or a small capacity modulator (for 3.3 V devices). And also to reduce the risk short circuit, a fuse is installed in the circuit, usually behind the zener diode. The physical connection is influenced by the form factor of the device in which the TL 431 circuit will be located, and environmental conditions (mainly temperature).

Stabilizer based on TL 431

The simplest stabilizer based on the TL 431 is a parametric stabilizer. To do this, you need to include two resistors R 1, R 2 in the circuit through which you can set the output voltage for TL 431 using the formula: U out = Vref (1 + R 1/ R 2). As can be seen from the formula here, the output voltage will be directly proportional to the ratio of R 1 to R 2. The integrated circuit will keep the voltage at 2.5 V. For resistor R 1, the output value is calculated as follows: R 1 = R 2 (U out / Vref - 1).

This regulator circuit is typically used in fixed or adjustable voltage. Such voltage stabilizers on the TL 431 can be found in printers, plotters, and industrial power supplies. If it is necessary to calculate the voltage for fixed power supplies, then we use the formula Vo = (1 + R 1/ R 2) Vref.

Timing relay

The precision characteristics of the TL 431 allow it to be used for other than its intended purpose. Due to the fact that the input current of this adjustable stabilizer is from 2 to 4 µA, then using this microcircuit you can assemble a temporary relay. The role of a timer in it will be played by R1, which will begin to gradually charge after opening the contacts S 1 C 1. When the voltage at the output of the stabilizer reaches 2.5 V, transistor DA1 will be open, current will begin to flow through the LEDs of the PC 817 optocoupler, and the open photoresistor will close the circuit.

Thermal stabilizer based on TL 431

The technical characteristics of TL 431 make it possible to create thermally stable current stabilizers based on it. In which resistor R2 acts as a feedback shunt, a value of 2.5 V is constantly maintained on it. As a result, the value of the load current will be calculated using the formula In = 2.5/R2.

Pinout and serviceability check of TL 431

The TL 431 form factor and its pinout will depend on the manufacturer. There are options in old TO-92 and new SOT-23 packages. Don’t forget about the domestic analogue: KR142EN19A is also widespread on the market. In most cases, the pinout is applied directly to the board. However, not all manufacturers do this, and in some cases you will have to look for information on pins in the data sheet of a particular device.

TL 431 is an integrated circuit and consists of 10 transistors. Because of this, it is impossible to check it with a multimeter. To check the serviceability of the TL 431 chip, you need to use a test circuit. Of course, there is often no point in looking for a burnt-out element and it is easier to replace the entire circuit.

Calculation programs for TL 431

There are many sites on the Internet where you can download calculator programs to calculate voltage and current parameters. They can indicate the types of resistors, capacitors, microcircuits and other components schemes. TL 431 calculators are also available online, they are inferior in functionality to installed programs, but if you only need the input/output and maximum values ​​of the circuit, then they will cope with this task.

In this article, we will learn how the TL431 integrated voltage regulator works, in adjustable blocks nutrition.

Technically TL431 called a programmable shunt regulator, in simple words it can be defined as adjustable zener diode. Let's look at its specifications and application instructions.

Zener diode TL431 has the following main functions:

• Output voltage is set or programmable up to 36 volts
• Low output impedance about 0.2 ohm
• Throughput up to 100 mA
• Unlike conventional Zener diodes, the noise generation in the TL431 is negligible.
• Fast switching.

General description of TL431

TL431 is an adjustable or programmable voltage regulator.
The required output voltage can be set using just two external (voltage divider) connected to the REF pin.

The diagram below shows the internal block diagram device, as well as PIN code designation.

TL431 pinout

Connection diagram for zener diode TL431

Now let's see how this device can be used in practical schemes. The diagram below shows how the TL431 can be used as a regular voltage regulator:

The above figure shows how, using just a couple of resistors and a TL431, you can create a regulator that operates in the 2.5 to 36 volt range. R1 is a variable resistor that is used to regulate the output voltage.

The following formula is valid for calculating the resistance of resistors if we want to obtain some fixed voltage.

Vo = (1 + R1/R2)Vref

When using 78xx series stabilizers (7805,7808,7812..) and TL431 together, you can use the following scheme:

TL431 cathode is connected to the 78xx common pin. The output of the 78xx is connected to one of the resistor voltage divider points, which determines the output voltage.

The above circuits using the TL431 are limited to an output current of 100mA maximum.

The following circuit can be used to obtain higher output current.

In the above circuit, most of the components are similar to the conventional regulator above, except here the cathode is connected to the positive through a resistor and the base of the buffer transistor is connected to their connection point. The output current of the regulator will depend on the power of this transistor.

Applications for TL431

The above applications of the TL431 can be used anywhere where precision output voltage or reference voltage settings are required. It is currently widely used in pulsed sources power supply to generate an accurate reference voltage.

(downloads: 846)

There are many famous, iconic, innovative and at the same time simple designs integrated circuits that exceeded the expectations of their creators, became popular and even somehow influenced the development of electronics. One of them – controlled zener diode tl431. Made in 1978, the tl431 chip is still widely used in many professional and amateur projects.

Performance characteristics tl431

To get an idea of ​​the design of the tl431, you need to study the datasheet of the device or the description of the microcircuit in Russian, which can be found on the Internet.

Often the tl431 system is presented in the form of a comparator or a specific transistor with a reference voltage of 2.5 V and a saturation voltage of about 2 V. The transistor opens when the voltage between the anode (Anode) and input (Reference) terminal reaches 2.5 V, the current begins flow from anode to cathode. If the voltage is below the opening value, the transistor is turned off. Interpreting the TL circuit in the form of such a transistor makes it easier to understand its operation.

In fact, it is an integrated circuit with an expanded internal structure consisting of several transistors, resistors and capacitors.

The datasheet presents various system parameters, the main performance characteristics being:

1. Maximum cathode voltage – 36 V;
2. The source is very stable, with a temperature drift usually around 3-7 mV;
3. Input current (Ref) is 1-5 µA;
4. The minimum value of cathode current is recommended 1 mA, the maximum – 100 mA.

Advantagestl431:

• adjustable voltage;
• consumes little energy;
• protects the battery from deep discharge;
• can be used as an adjustable Z-diode and as a controlled amplifier;
• has only three contacts;
• low cost.

The pinout of the microcircuit depends on the manufacturer and may vary. If radio amateurs desolder tl431 from any board, then the pinout will be visible on it.

The tl431 pinout with several versions is shown in the figure.

Connection diagram

For tl431, the connection diagram depends on the purpose for which the device is intended. Its simplest application – stabilization of voltage at a given value.

A voltage divider made using a pair of resistors is connected to the tl431 input. Taking into account the technical data of the microcircuit, the required resistance can be calculated.

Let's say you need to get 5 V at the output. Calculations are carried out based on the formula:

Vout = (1 + R1/R2) x Vref.

The full formula is written as:

Vout = (1 + R1/R2) x Vref + (Iref x R1), but the second part of the equation can be ignored as it is a very small value, although this will depend on the circuit used.

1. 5 V = (1 + R1/R2) x 2.5;
2. R1/R2 = 1.

Since the resistance ratio is 1, two resistors with the same resistance must be used.

Second example for 2.75V output voltage:

1. 2.75 V = (1 + R1/R2) x 2.5;
2. R1/R2 = 0.1.

For example, if one resistor is taken with a resistance of 1 kOhm, then the other – should be 10 kOhm.

As a result, the reference voltage is kept at 2.5 V; by choosing different divider resistances, you can create a voltage setpoint stabilizer.

Important! If it is necessary to stabilize the 2.5 V voltage, the divider is not used, and the input pin of tl431 is connected to the cathode.

The tl431 microcircuit is also used as a current stabilizer. Here the formula is used to calculate the resistance at the desired current:

R2 = Vref/Io, where:

• R2 – resistance,
• Io – desired current.

Since the voltage Vref = 2.5 V, then R2 = 2.5/Io. In this case, through resistance R2, feedback to maintain the input voltage level Vref.

Circuits with sensors

In many circuits it is necessary to monitor parameters using various sensors (photoresistors, thermistors). General scheme it turns out similar to that for the divider, with the exception of replacing one of the resistances. In its place, for example, a thermistor is installed, and the tl431 cathode is connected to the relay coil. The temperature value is set using a potentiometer. When the temperature exceeds the operating limit, the resistance ratio changes, the voltage at the control contact tl431 exceeds the opening level, current is passed to the relay coil having make contacts in the load circuit.

Charger

For chargers It is important to limit the charging current and voltage parameters to avoid damaging the batteries. Such a circuit can easily be implemented using an integrated circuittl431 and other elements:

1. If the output voltage has not reached 4.2 V, regulation charging current carried out through transistors and resistors;
2. Once the value reaches 4.2 V, the output voltage of the memory is controlled by tl431, not allowing it to rise further.

Checking the chip

Radio amateurs are wondering how to check tl431 with a multimeter? A simple test of a microcircuit is impossible, because it contains many elements. But there is a way to check the functionality of the device by assembling a special circuit from resistors, a button and the TL circuit itself. Connecting a multimeter to the output of the circuit will now help determine the serviceability of the tl431.