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Scheme for switching on the zener diode tl431 and checking the microcircuit with a multimeter. TL431 switching circuit, TL431 pinout Voltage boost indicator

Chip TL431 It's an adjustable zener diode. It is used as a reference voltage source in the circuits of various power supplies.

Specifications TL431

  • output voltage: 2.5 ... 36 volts;
  • output impedance: 0.2 ohm;
  • direct current: 1…100 mA;
  • error: 0.5%, 1%, 2%;

TL431 has three outputs: cathode, anode, input.

TL431 analogues

Domestic analogues of TL431 are:

  • KR142EN19A
  • K1156EP5T

Foreign analogues include:

  • KA431AZ
  • KIA431
  • HA17431VP
  • IR9431N
  • AME431BxxxxBZ
  • AS431A1D
  • LM431BCM

Wiring diagrams TL431

The TL431 zener diode chip can be used not only in power circuits. On the basis of TL431, you can design all kinds of light and sound signaling devices. With the help of such structures, it is possible to control many different parameters. The most basic parameter is voltage control.

By translating some physical indicator with the help of various sensors into a voltage indicator, it is possible to manufacture a device that monitors, for example, temperature, humidity, liquid level in a container, degree of illumination, gas and liquid pressure. below are several schemes for switching on a controlled zener diode TL431.

This circuit is a current stabilizer. Resistor R2 acts as a shunt, on which a voltage of 2.5 volts is set due to feedback. As a result of this, at the output we get a constant current equal to I \u003d 2.5 / R2.

Overvoltage indicator

The operation of this indicator is organized in such a way that when the potential at the TL431 control contact (pin 1) is less than 2.5V, the TL431 zener diode is locked, only a small current passes through it, usually less than 0.4 mA. Since this amount of current is enough for the LED to glow, to avoid this, you just need to connect a resistance of 2 ... 3 kOhm in parallel with the LED.

If the potential supplied to the control pin exceeds 2.5 V, the TL431 chip will open and HL1 will start to burn. Resistance R3 creates the desired current limit flowing through HL1 and the Zener diode TL431. The maximum current passing through the TL431 zener diode is in the region of 100 mA. But the maximum allowable current for an LED is only 20 mA. Therefore, a current-limiting resistor R3 must be added to the LED circuit. Its resistance can be calculated using the formula:

R3 \u003d (Upit. - Uh1 - Uda) / Ih1

where Upit. - supply voltage; Uh1 - voltage drop across the LED; Uda - voltage on open TL431 (about 2 V); Ih1 - the required current for the LED (5 ... 15mA). It must also be remembered that for the TL431 zener diode, the maximum allowable voltage is 36 V.

The voltage value Uz at which the signaling device is triggered (the LED is lit) is determined by the divider on the resistances R1 and R2. Its parameters can be calculated by the formula:

R2 \u003d 2.5 x Rl / (Uz - 2.5)

If it is necessary to accurately set the response level, then it is necessary to install a tuning resistor with a higher resistance in place of the resistance R2. After finishing fine tuning, this trimmer can be replaced with a permanent one.

Sometimes it is necessary to check several voltage values. In this case, you will need several similar signaling devices on the TL431 tuned to their voltage.

Checking the health of the TL431

The above circuit can test TL431 by replacing R1 and R2 with a single 100 kΩ variable resistor. If, by rotating the variable resistor slider, the LED lights up, then the TL431 is working.

Low voltage indicator

The difference between this circuit and the previous one is that the LED is connected differently. This connection is called inverse, since the LED lights up only when the TL431 chip is locked.

If the controlled voltage value exceeds the level determined by the divider Rl and R2, the TL431 chip opens, and the current flows through the resistance R3 and pins 3-2 of the TL431 chip. On the microcircuit at this moment there is a voltage drop of about 2V, and it is clearly not enough for the LED to glow. To completely prevent the LED from lighting up, 2 diodes are additionally included in its circuit.

At the moment when the value under study is less than the threshold determined by the divider Rl and R2, the TL431 chip will close, and the potential at its output will be much higher than 2V, as a result of which the HL1 LED will light up.

Voltage change indicator

If you only need to monitor the change in voltage, then the device will look like this:

This circuit uses a two-color LED HL1. If the potential is below the threshold set by the divider R1 and R2, then the LED lights up green, if it is above the threshold value, then the LED lights up red. If the LED does not glow at all, then this means that the controlled voltage is at the level of the specified threshold (0.05 ... 0.1V).

Work TL431 together with sensors

If it is necessary to monitor the change in some physical process, then in this case the resistance R2 must be changed to a sensor characterized by a change in resistance due to external influence.

An example of such a module is shown below. To summarize the principle of operation, various sensors are shown in this diagram. For example, if you use as a sensor, then in the end you get a photorelay that reacts to the degree of illumination. As long as the illumination is high, the resistance of the phototransistor is small.

As a result, the voltage at the control contact TL431 is below the specified level, because of this, the LED does not light up. As the illumination decreases, the resistance of the phototransistor increases. For this reason, the potential at the control contact of the zener diode TL431 increases. When the operating threshold (2.5V) is exceeded, HL1 lights up.

This circuit can be used as a soil moisture sensor. In this case, instead of a phototransistor, two stainless electrodes should be connected, which are stuck into the ground at a short distance from each other. After the soil dries, the resistance between the electrodes increases and this leads to the operation of the TL431 chip, the LED lights up.

If, however, a thermistor is used as a sensor, then a thermostat can be made from this circuit. The level of operation of the circuit in all cases is set by means of the resistor R1.

TL431 in a circuit with sound indication

In addition to the above light devices, a sound indicator can also be made on the TL431 chip. A diagram of such a device is shown below.

This sound signaling device can be used as a control over the water level in any container. The sensor consists of two stainless electrodes located at a distance of 2-3 mm from each other.

As soon as the water touches the sensor, its resistance will decrease, and the TL431 microcircuit will enter the linear mode of operation through the resistances R1 and R2. In this regard, self-generation appears at the resonant frequency of the emitter and an audible signal will be heard.

Calculator for TL431

To facilitate the calculations, you can use the calculator:


(103.4 Kb, downloaded: 21 590)
(702.6 Kb, downloaded: 14 618)

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 noteworthy.

What is this TL431 reference voltage source?

In power supplies for personal computers, you can find a reference voltage source chip (ION) TL431.

You can think of it as an adjustable zener diode.

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

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

The fact is that the microcircuits that make up a computer - both large and small - can only work 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 the voltage.

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

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

Thus, we do not need to look for zener diodes for a certain 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 plugged 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, part of the components of the computer motherboard is under this voltage..

It is with the help of it that the main part of the power supply is launched - by a signal from the motherboard. The TL431 chip is also often involved in the formation of this voltage.

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

How can this threaten us?

If the voltage + 5VSB is more than necessary, the computer may “freeze”, as part of the motherboard chipset is powered by increased voltage.

Sometimes this behavior of the computer 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 troubleshooting. And you just had to measure the voltage of the source on duty!

Recall that the +5VSB voltage must be within 5% 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 out” this microcircuit as a regular zener diode.

To make sure it works, you need to assemble a small circuit for testing.

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

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

When the button S1 is closed, the output voltage will have a value of 2.5 V (reference voltage), when it is released, it will have a value of 5 V.

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

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

To check 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 socket, the output voltage will be approximately 10 V.

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

*Datasheet is reference data (data sheets) for electronic components. They can be found with a search engine on the Internet.

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

During the repair, there was a clear need to first of all check the serviceability of the reference voltage source, but did not check it, put it off for later and did what could be delayed. I understood that I was "stupid", but I could not do anything. There was no tester to check the TL431. Once again, it was already unbearable to solder the parts of the test circuit “on the knee”. And how I didn’t want to be distracted from the repair that had begun, but I had to. It warmed my soul that the next time I needed to check T-elka there would be no problems.

Electrical Tester Diagram

In the virtual space of the Internet, there are many schemes for such a check. I saw the difference between them in the fact that some report - they signal the health of the electronic component by flashing - lighting up the LEDs, others create the prerequisites for measuring the output voltage, by which value one should judge the health of the TL431. On the one hand, the first ones seem to be self-sufficient, in addition to the second, a voltmeter is needed. On the other hand, the former need to “take their word for it”, while the latter do not “decide” anything themselves, but give out objective information for making a decision. In addition, a voltmeter is always at hand. I chose the second option, it is also even simpler, the “issue price” is three fixed resistors.

For a suitable case, to put everything you need into it, it won’t get up, the site has an article “Manufacturing a power plug with a non-standard case”. I started with the equipment of the top cover of the case, for this I needed a three-pin socket, a push button and a notebook sheet in a box on which a circle was drawn in accordance with the diameter of the cover and with an awl, the places for installing the socket and button were marked. The cut circle has already become a template, was placed on the lid and the corresponding markings were made on it with an awl. Further, with the same awl, holes of the required diameter were pierced for the contacts of the socket and button.

So, a socket and a button are installed on the top cover (their contacts are bent from the inside and soldered with tin), on the middle part of the case, as a power connector, there is a “tulip”, on the bottom cover there are pins for connecting to a multimeter. The fact that some parts (two lids and a neck) of a plastic container (milk bottle) acted as a body is probably clear and without explanation.

It remains to mount the circuit itself on the inside of the cover, on the contacts of the socket and button, first of all, I installed three resistors, and all the connecting wires were soldered to the second. There were unexpectedly a lot of wires, there is no need to rush here - it is no wonder to confuse.

This time I did not use glue for additional fastening, but “planted” everything on small self-tapping screws. Three pieces for each element. So it is more maintainable, although it is unlikely that it will be necessary to repair anything here. The probe is assembled, once and for all. It remains to check its operation and, accordingly, the serviceability of the TL431 reference voltage sources available.

Video

Since the case has “burned out” and the probe is now there, it remains to remember this and be able, if necessary, to quickly identify it from among others in the same cases that are in the box intended for this. And you also need to remember that the operating voltage of the probe is 12 volts, that with the TL431 not connected, the multimeter will show a voltage of 10 volts, with 5 volts connected, and with the button pressed 2.5 volts, and in addition, correctly install the component under test in the socket. And you can not especially remember, but arrange the front panel accordingly. Project author: Babay from Barnaula.

Discuss the article CHECKING THE REFERENCE VOLTAGE SOURCE TL431

TL431 is an integral zener diode. In the circuit, it plays the role of a reference voltage source. The presented element is used, as a rule, in power supplies. The device at the zener diode is quite simple. In total, the model uses three outputs. Depending on the modification, up to ten transistors can be located in the case. A distinctive feature of TL431 is considered to be good thermal stability.

Switching circuit for 2.48 V

The TL431 zener diode has a 2.48 V switching circuit with a single-stage converter. On average, the operating current in the system reaches a level of 5.3 A. Resistors for signal transmission can be used with different voltage conductivity. The stabilization accuracy in these devices varies around 2%.

To increase the sensitivity of the zener diode, various modulators are used. As a rule, it is the dipole type that is selected. On average, their capacitance is not more than 3 pF. However, in this case, much depends on the conductivity of the current. To reduce the risk of overheating of the elements, expanders are used. The zener diodes are connected through the cathode.

Turning on a 3.3V device

At the TL431 zener diode, the 3.3V switching circuit implies the use of a single-stage converter. Resistors for pulse transmission are of a selective type. Even at the TL431 zener diode, the 3.3 volt switching circuit has a small capacity modulator. To reduce the risk, fuses are used. They are usually installed behind the zener diodes.

To amplify the signal, you can not do without filters. On average, the threshold voltage fluctuates around 5 watts. The operating current of the system is no more than 3.5 A. As a rule, the stabilization accuracy does not exceed 3%. It is also important to note that the zener diode can be connected via a vector adapter. In this case, the transistor is selected as a reasonable type. On average, the modulator capacitance should be 4.2 pF. Thyristors are used both phase and open type. To increase current conduction, triggers are needed.

To date, these elements are equipped with amplifiers of different capacities. On average, the threshold voltage in the system reaches 3.1 W. The operating current indicator fluctuates around 3.5 A. It is also important to consider the output resistance. The presented parameter must be no more than 80 ohms.

Connection to 14 V circuit

At the TL431 zener diode, the 14V switching circuit implies the use of a scalar converter. On average, the threshold voltage is 3 watts. As a rule, the operating current does not exceed 5 A. At the same time, the permissible overload fluctuates around 4 Ah. Also, the TL431 zener diode has a 14V switching circuit with amplifiers of both single-pole and two-pole types. In order to improve conductivity, one cannot do without a tetrode. It can be used with one or two filters.

A Series Zener Diodes

For power supplies and inverters, the A TL431 series are used. How to check if an element is connected correctly? In fact, this can be done using a tester. The threshold resistance indicator must be 80 ohms. The device is capable of operating through single-stage and vector type converters. Resistors in this case are used with a lining.

If we talk about the parameters, then the circuit does not exceed 5 watts. In this case, the operating current fluctuates around 3.4 A. Expanders are used to reduce the risk of transistor overheating. For A-series models, they only fit the switched type. To increase the sensitivity of the device, powerful modulators are needed. On average, the output resistance parameter does not exceed 70 ohms.

CLP series devices

Zener diodes TL431 switching circuit has single-stage converters. You can meet the CLP model both in inverters and in many household appliances. The threshold voltage of the zener diode fluctuates around 3 watts. The direct operating current is 3.5 A. The stabilization accuracy of the elements does not exceed 2.5%. Different types of modulators are used to adjust the output signal. Triggers in this case are selected with amplifiers.

ACLP Series Zener Diodes

Zener diodes TL431 switching circuit has vector or scalar converters. If we consider the first option, then the operating current level is no more than 4 A. In this case, the stabilization accuracy is approximately 4%. To amplify the signal, triggers are used, as well as thyristors.

If we consider the connection scheme with a scalar converter, then modulators are used with a capacitance of about 6 pF. Directly transistors are used resonant type. To amplify the signal, conventional triggers are suitable. It is also important to note that the sensitivity index of the device fluctuates around 20 mV.

AC Models

For dipole inverters, cherry AC TL431 zener diodes are often used. How to check the functionality of the connected element? This can be done using a regular tester. The output resistance parameter must be no more than 70 ohms. It is also important to note that the devices of this series are switched on via a vector converter.

In this case, scalar modifications are not suitable. This is largely due to the low current conduction threshold. It is also important to note that the nominal voltage does not exceed 4 watts. The operating current in the circuit is maintained at 2 A. Various thyristors are used to reduce heat losses. To date, expansion and phase modifications are being produced.

Models with KT-26 case

In household electrical appliances, TL431 zener diodes are often found with the KT-26 case. The switching circuit implies the use of dipole modulators. They are produced with different current conductivity. The maximum sensitivity parameter of the system fluctuates around 430 mV.

Directly output impedance reaches no more than 70 ohms. Triggers in this case are used only with amplifiers. To reduce the risk of short circuits, open and closed type filters are used. Direct connection of the zener diode is carried out through the cathode.

Housing KT-47

TL431 (stabilizer) with a KT-47 case can be found in power supplies of various capacities. The element inclusion scheme implies the use of vector converters. The modulator for circuits is suitable for capacities up to 4 pF. The direct output impedance of the devices is approximately 70 ohms. To improve the conductivity of zener diodes, only beam-type tetrodes are used. As a rule, the stabilization accuracy does not exceed 2%.

For 5 V power supplies

In 5 V power supplies, the TL431 is switched on through amplifiers with different current conductivity. Directly converters are used single-stage type. Also, in some cases, vector modifications are applied. The average output impedance is about 90 ohms. The stabilization accuracy rate in devices is 2%. Block expanders are used in both switched and open types. Triggers can only be used with filters. Today they are produced with one and several elements.

Wiring diagram for 10 V blocks

The scheme for including a zener diode in a power supply involves the use of a single-stage or vector converter. If we consider the first option, then the modulator is selected with a capacitance of 4 pF. In this case, the trigger is used only with amplifiers. Sometimes filters are used to increase the sensitivity of the zener diode. The circuit threshold voltage averages 5.5 watts. The operating current of the system fluctuates around 3.2 A.

The stabilization parameter, as a rule, does not exceed 3%. If we consider a circuit with a vector converter, then we cannot do without a transceiver. It can be used either open or chromatic. The modulator is installed with a capacitance of 5.2 pF. The expander is quite rare. In some cases, it is able to increase the sensitivity of the zener diode. However, it is important to take into account that the thermal losses of the element increase significantly.

Schematic for 15 V blocks

The TL431 zener diode is switched on through a 15 V block using a single-stage converter. In turn, the modulator is suitable with a capacitance of 5 pF. Resistors are used exclusively selective type. If we consider modifications with triggers, then the threshold voltage parameter does not exceed 3 W. The stabilization accuracy is around 3%. Filters for the system are suitable for both open and closed types.

It is also important to note that an expander can be installed in the circuit. To date, models are produced mainly of the switched type. For modifications with transceivers, the current conductivity does not exceed 4 microns. In this case, the sensitivity index of the zener diode fluctuates around 30 mV. The output impedance in this case reaches approximately 80 ohms.

For automotive inverters

For often used AC series zener diodes TL431. The switching circuit in this case involves the use of two-digit triodes. Directly filters are applied open type. If we consider circuits without an expander, then the threshold voltage fluctuates around 10 watts.

The direct operating current is 4 A. The system overload parameter is allowed at 3 mA. If we consider modifications with expanders, then in this case high-capacity modulators are installed. Resistors are used as standard selective type.

In some cases, amplifiers of different power are used. The threshold voltage parameter, as a rule, does not exceed 12 W. The output impedance of the system can range from 70 to 80 ohms. The stabilization accuracy index is approximately 2%. The operating current of the systems is no more than 4.5 A. The zener diodes are directly connected through the cathode.

TL431 working principle and very simple test. It was not in vain that I again touched on this topic, this is one of the most mass-produced integrated circuits.

Its release started in 1978. She gained great popularity when using various switching power supplies for TVs, tuners, DVDs and other audio-video equipment. And it often works in tandem with a very popular radio component - an optocoupler.

For those readers who find it easier to perceive information by ear, I advise you to watch the video at the very bottom of the page.

The Tl431 is a precision controlled voltage reference.

It gained its popularity due to its very low cost and high reliability and accuracy. The principle of its operation is quite simple to understand from the block diagrams.

If the voltage at the input of the source is lower than the reference voltage, then the output of the operational amplifier is also low voltage, respectively, the transistor is closed and the current from the cathode to the anode does not flow (more precisely, it is very small, does not exceed 1 milliamp).

TL431 equivalent circuit

The equivalent circuit of this microcircuit can be represented as an ordinary zener diode. Where the stabilization voltage can be calculated using the formula below:

One of the simplest types of stabilizers is parametric.

Parametric: in such a stabilizer, a CVC section of the device is used, which has a large steepness (Wikipedia). It can also be done on the tl431 chip.

To do this, you need only three resistors, two of which will control the input of the microcircuit and, as it were, program the output voltage. The output voltage can be calculated using the formula Uout=Vref(1 + R1/R2). Wherein Vref=2.5V
R1=R2(Uout/Vref - 1).
In addition to resistors R1 and R2, the circuit also contains resistor R3; its purpose, like for a simple zener diode, is a current limiter
Main technical characteristics of TL431:
anode-cathode voltage: 2.5 ... 36 volts;
anode-cathode current: 1 ... 100 mA (if you need stable operation, then you should not allow a current less than 5 mA);

Compensation Voltage Stabilizer

Compensatory: has feedback.

In it, the voltage at the output of the stabilizer is compared with the reference one, from the difference between them a control signal is formed for the regulating element.
To increase the stabilization currents of one transistor becomes small, an intermediate amplifying stage is needed.

Now briefly the purpose of the components: Resistor R2, it is the current limiter of the base of the transistor vt1, you can use from 300 to 400 ohms. Resistor R3 compensates for the reverse collector current of transistor vt2, you can use a 4.7 kΩ resistor. Capacitor C1 increases the stability of the stabilizer at high frequencies, you can use 0.01 uF.

Current stabilizer on TL431

On the tl431 chip, you need to assemble a thermally stable current stabilizer.

Resistor R2, together with transistor vt1, is a kind of shunt on which a voltage of 2.5 volts is maintained using feedback. You can calculate the stabilization current by the formula In=2.5/R2.

Voltage boost indicator on TL431

The LED turns on when the voltage exceeds the set threshold. Which can be calculated using the formula:

R2 \u003d 2.5 x Rl / (Uz - 2.5)

Voltage change indicator on TL431

Here, the LEDs will light up depending on whether the voltage has exceeded or, on the contrary, has become below the specified threshold.

Connecting sensors

The sensors are connected as one of the divider arms to the control contact of the stabilizer

One of the simple methods for checking TL431

you need to close its cathode and control electrode

and it should show like an ordinary 2.5 volt zener diode. To do this, you can use a Chinese tester, it will show as two oncoming diodes, one as an ordinary idiot and the other as a two and a half volt zener diode