Controlled zener diode TER 3 431. Description of the adjustable zener diode TL431

The production of integrated circuits began back in 1978 and continues to this day. The microcircuit makes it possible to produce different kinds alarms and charging device for everyday use. Found the tl431 chip wide application in household appliances: monitors, tape recorders, tablets. TL431 is a kind of programmable voltage regulator.

Connection diagram and principle of operation

The principle of operation is quite simple. The stabilizer has a constant reference voltage, and if the supplied voltage is less than this rating, the transistor will be closed and will not allow current to flow. This can be clearly seen in the following diagram.

If this value is exceeded, the adjustable zener diode will open P-N junction transistor, and the current will flow further to the diode, from plus to minus. The output voltage will be constant. Accordingly, if the current drops below the reference voltage, the controlled operational amplifier will shut down.

Pinout and technical parameters

The operational amplifier is available in different packages. Initially it was a TO-92 hull, but over time it was replaced by a newer version, SOT-23. Below is the pinout and types of housings, starting with the most “ancient” one and ending with the updated version.

In the figure you can see that the tl431 pinout varies depending on the type of case. tl431 has domestic analogs KR142EN19A, KR142EN19A. There are also foreign analogues of tl431: KA431AZ, KIA431, LM431BCM, AS431, 3s1265r, which are in no way inferior to the domestic version.

Characteristics of TL431

This op amp operates from 2.5V to 36V. The operating current of the amplifier ranges from 1A to 100 mA, but there is one important nuance: if stability in the operation of the stabilizer is required, then the current should not fall below 5 mA at the input. The TL431 has a reference voltage value which is determined by the 6th letter in the marking:

• If there is no letter, then the accuracy is 2%.
• The letter A in the marking indicates - 1% accuracy.
• The letter B indicates - 0.5% accuracy.

More detailed technical specifications shown in Fig. 4

In the description of the tl431A, you can see that the current value is quite small and amounts to the stated 100 mA, and the amount of power that these cases dissipate does not exceed hundreds of milliwatts. This is not enough. If you have to work with more serious currents, then it would be more correct to use powerful transistors with improved parameters.

Stabilizer check

A pertinent question immediately arises: how to check tl431 with a multimeter. As practice shows, you won’t be able to check with just a multimeter. To test the tl431 with a multimeter, you should assemble a circuit. To do this you will need: three resistors (one of them is trimmer), an LED or light bulb, a source direct current 5V.

Resistor R3 must be selected in such a way that it limits the current to 20 mA in the power circuit. Its nominal value is approximately 100 ohms. Resistors R2 and R3 act as a balancer. As soon as the voltage is 2.5 V at the control electrode, the LED junction will open and the voltage will flow through it. This circuit is good because the LED acts as an indicator.

The DC source - 5V is fixed, and the tl431 microcircuit can be controlled using a variable resistor R2. When power is not supplied to the microcircuit, the diode does not light up. After the resistance is changed using a trimmer, the LED lights up. After this, the multimeter must be switched to DC measurement mode and measure the voltage at the control terminal, which should be 2.5. If voltage is present and the LED is on, then the element can be considered working.

Based on the operational current amplifier tl431, you can create a simple stabilizer. To create the required U value, three resistors will be needed. It is necessary to calculate the nominal value of the programmed voltage of the stabilizer. The calculation can be made using the formula: Uout=Vref(1 + R1/R2). According to the formula, U at the output depends on the values ​​of R1 and R2. The higher the resistance of R1 and R2, the lower the output stage voltage. Having received the rating of R2, the value of R1 can be calculated as follows: R1=R2(Uout/Vref – 1). The adjustable stabilizer can be activated in three ways.

It is necessary to take into account an important nuance: the resistance R3 can be calculated using the formula by which the ratings of R2 and R2 were calculated. You should not install a polar or non-polar electrolyte in the output stage to avoid interference at the output.

Mobile phone charger

The stabilizer can be used as a kind of current limiter. This property will be useful in devices for charging mobile phones.

If the voltage in the output stage does not reach 4.2 V, the current in the power circuits is limited. After reaching the declared 4.2 V, the stabilizer reduces the voltage value - therefore, the current value also drops. Circuit elements VT1 VT2 and R1-R3 are responsible for limiting the current value in the circuit. Resistance R1 bypasses VT1. After exceeding 0.6 V, the VT1 element opens and gradually limits the voltage supply to the bipolar transistor VT2.

Based on transistor VT3, the current value decreases sharply. Transitions are gradually closing. The voltage drops, which causes the current to drop. As soon as U approaches 4.2 V, the tl431 stabilizer begins to reduce its value in the output stages of the device, and the charge stops. To manufacture the device, you must use the following set of elements:

Necessary reverse Special attention for transistor az431. To uniformly reduce the voltage in the output stages, it is advisable to install the az431 transistor; the datasheet of the bipolar transistor can be seen in the table.

It is this transistor that smoothly reduces the voltage and current. The current-voltage characteristics of this element are well suited for solving the task.

The TL431 operational amplifier is multifunctional element and makes it possible to design various devices: chargers for mobile phones, alarm systems and much more. As practice shows, an operational amplifier has good characteristics and is not inferior to foreign analogues.

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 of 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 range of applications. 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 phone batteries.

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;
• Operating temperature range 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 environmental factors. 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. In case output voltage will exceed the programmed level, the transistor will be open and electricity 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 of a 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 the conditions environment(mostly temperature).

Stabilizer based on TL 431

The simplest stabilizer based on TL 431 is 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 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 scheme. 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.

Let me make a reservation right away that this article is not a panacea. This may not work for some people.

First, I'll talk about the TL431 and what it does. TL431 is a controlled zener diode with which you can obtain a stabilized voltage within a wide range from 2.5 volts to 36 volts. Using this microcircuit, you can make a reference voltage source for power supplies, as well as for various measuring circuits.

Figure taken from ON Semiconductor datasheet

Below are two datasheet options for this chip.

1. ON Semiconductor datasheet https://www.onsemi.com/pub/Collateral/TL431-D.PDF
2. Texas Instruments datasheet http://www.ti.com/lit/ds/symlink/tl431.pdf

The pinout of this chip is best displayed in the ON Semiconductor datasheet

One small detail found in the Texas Instruments datasheet

In all the figures there is one inscription “top view”, this translates as “top view”; if you look at the datasheet inattentively, without knowing what this may mean, you can solder it incorrectly on the board.

I used the TL431 chip in one of my circuits, and it turned out to be faulty. After searching the forums, I found a way to test this microcircuit. And in some places I saw how they call this microcircuit using a multimeter, but, alas, this is not all that. I also first tried to check with a multimeter but immediately put this event aside. And I decided to try checking it using a universal component tester, which I had previously purchased on Aliexpress.

During the check I made a table. First I checked in dual-terminal mode (if the table shows two pins, you just need to combine both pins together).

Measurement results of the first specimen

Dimension 1 – REF; 2 - cathode.

Dimension 1 – anode; 2 - cathode.

Dimension 1 - REF, cathode; 2 – anode.

Dimension 1 – REF; 2 – cathode, anode.

Measurement 1 – REF, 2 – anode, 3 – cathode.

Measurement results of the second specimen.

There is a slight difference. Looking at the table you notice a certain pattern. For example, in line 4, this is actually the operating mode of the TL431 to produce 2.5 volts. But the most interesting thing is the measurement mode in the three-terminal mode. In one case it is defined as a transistor, and in the second case as a missing part. The most interesting thing is when the transistor is defined: the NPN structure transistor is defined, the REF pin is defined as the emitter, the anode as the base, and the cathode as the collector. Between the REF and the cathode there is a cathode diode, which is directed towards the cathode.

Based on this data, it is already possible to judge whether the microcircuit has been fixed or not, as well as determine the pinout.

Good afternoon friends!

Today we will get acquainted with another piece of hardware that is used in computer technology. It is not used as often as, say, or, but also worthy of attention.

What is the TL431 voltage reference?

In power supplies personal computers You can find the TL431 reference voltage source (ION) chip.

You can think of it as an adjustable zener diode.

But this is precisely a microcircuit, since it contains more than a dozen transistors, not counting other elements.

A zener diode is a thing that maintains (seeks to maintain) a constant voltage across the load. “Why is this needed?” - you ask.

The fact is that the microcircuits that make up a computer - both large and small - can only operate in a certain (not very large) range of supply voltages. If the range is exceeded, their failure is very likely.

Therefore, in (not only computer) circuits and components are used to stabilize voltage.

For a certain range of voltages between the anode and cathode (and a certain range of cathode currents), the microcircuit provides a reference voltage of 2.5 V relative to the anode at its ref output.

Using external circuits (resistors), you can vary the voltage between the anode and cathode within a fairly wide range - from 2.5 to 36 V.

This way, we don't have to look for zener diodes for a specific voltage! You can simply change the resistor values ​​and get the voltage level we need.

In computer power supplies there is a standby voltage source + 5VSB.

If the power supply plug is inserted into the network, it is present on one of the pins of the main power connector - even if the computer is not turned on.

At the same time, some of the components motherboard the computer is under this voltage.

It is with its help that the main part of the power supply is started - by a signal from the motherboard. The TL431 microcircuit is often involved in the formation of this voltage.

If it fails, the value of the standby voltage may differ - and quite strongly - from the nominal value.

What could this threaten us with?

If the voltage +5VSB is more than necessary, the computer may freeze, since some of the motherboard microcircuits are powered by an increased voltage.

Sometimes this computer behavior misleads an inexperienced repairman. After all, he measured the main supply voltages of the power supply +3.3 V, +5 V, +12 V - and saw that they were within tolerance.

He starts digging elsewhere and spends a lot of time searching for the problem. But you just had to measure the voltage of the standby source!

Let us remind you that the voltage +5VSB must be within 5% of the tolerance, i.e. lie in the range of 4.75 - 5.25 V.

If the voltage of the standby source is less than necessary, the computer may not start at all..

How to check TL431?

It is impossible to “ring” this microcircuit like a regular zener diode.

To make sure it is working properly, you need to assemble a small circuit for testing.

In this case, the output voltage, to a first approximation, is described by the formula

Vo = (1 + R2/R3) * Vref (see datasheet*), where Vref is the reference voltage equal to 2.5 V.

When the S1 button is closed, the output voltage will be 2.5 V (reference voltage), and when it is released, it will be 5 V.

Thus, by pressing and releasing the S1 button and measuring the signal at the output of the circuit, you can verify the serviceability (or malfunction) of the microcircuit.

The test circuit can be made as a separate module using a 16-pin DIP connector with a pin pitch of 2.5 mm. The power supply and probes of the tester are connected to the output terminals of the module.

To test the microcircuit, you need to insert it into the connector, press the button and look at the tester display.

If the chip is not inserted into the connector, the output voltage will be approximately 10 V.

That's all! Simple, isn't it?

*Datasheets are reference data sheets for electronic components. They can be found by searching on the Internet.

Victor Geronda was with you. See you on the blog!

I needed an inexpensive reference voltage source here. After looking through the catalogs, I chose the TL431 chip for 20 rubles. Now I’ll tell you what kind of insect this is and how to use it.

TL431

TL431 is a so-called programmable zener diode. Used as a voltage reference and power supply for low-power circuits. Produced by several manufacturers and in different packages, I got it from Texas Instruments in the SOT23 package.

Specifications:

Output voltage from 2.5 to 36 V
- operating current from 1 to 100 mA
- output impedance 0.2 Ohm
- accuracy 0.5%, 1% and 2%

Has three outputs. There are two like a standard zener diode - anode and cathode. And a reference voltage pin that connects to the cathode or midpoint of the voltage divider. On foreign diagrams it is indicated as follows:

The minimum switching circuit requires one resistor and allows for a reference voltage of 2.5 V.

The resistor in this circuit is calculated using the following formula:

where Ist is the TL431 current, and Il is the load current. The input current of the reference pin is not taken into account since it is ~2 µA.

In a complete circuit, two more resistors are added to TL431, but in this case an arbitrary output voltage can be obtained.

The voltage divider resistor values ​​and the TL431 output voltage are related as follows:

,where Uref = 2.5 V, Iref = 2 µA. These are typical values ​​and they have a certain spread (see datasheet).

If you specify the value of one of the resistors and the output voltage, you can calculate the value of the second resistor.

And knowing the output voltage and input current, you can calculate the value of resistor R1:

,where Iin is the input current of the circuit, which is the sum of the operating current of the TL431, the voltage divider current and the load current.

If TL431 is used to obtain the reference voltage, then resistors R2 and R3 must be taken with an accuracy of 1% from the E96 series.

Calculation of voltage stabilizer on TL431

Initial data

Input voltage Uin = 9 V
Required output voltage Uout = 5 V
Load current Il = 10 mA

Data from the datasheet:

Ist = 1..100 mA
Iref = 2 µA
Uref = 2.495 V

Calculation

We set the value of resistor R2. The maximum value of this resistor is limited by the current Iref = 2 µA. If we take the value of resistor R2 equal to units/tens of kOhms, then this will do. Let R2 = 10 kOhm.

Since TL431 is used as a power supply, high precision is not needed here and the Iref*R2 term can be neglected.

The rounded value of R3 will be 10 kOhm.

The voltage divider current is Uout/(R1+R2) = 5/20000 = 250 µA.

The TL431 current can be from 1 to 100 mA. If we take the current Ist > 2 mA, then the divider current can be neglected.

Then the input current will be equal to Iin = Ist + Il = 2 + 10 = 12 mA.

And the rating R1 = (Uin - Uout)/Iin = (9 - 5)/0.012 = 333 Ohm. Round up to 300.

The power dissipated by resistor R1 is (9 - 5)*0.012 = 0.05 W. On other resistors it will be even less.

R1 = 300 Ohm
R2 = 10 kOhm
R3 = 10 kOhm

Something like this, without taking into account the nuances.

Load capacity

If you use a TL431 and place a capacitor at the output, the microcircuit may “buzz”. Instead of reducing the output noise, a periodic sawtooth signal of several millivolts will appear at the cathode.

The load capacitance at which the TL431 behaves stably depends on the cathode current and output voltage. Possible capacity values ​​are shown in the picture from the datasheet. Stable areas are those outside the charts.