Questions tagged [tl431]

For questions about the three-terminal shunt regulator. Use in conjunction with the "voltage-regulator" or "voltage-reference" tags, as applicable.

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Designing A Circuit To Light An LED When Voltage Drops Below Threshold

I'm a beginner with designing circuits and I'm attempting this because I'm trying to design my first PCB. The basic idea is that I have a 12V battery as a power source and I want an LED to light up ...
46 views

How can I calculate the max. allowable load for my reference voltage?

I have a 2.5V reference voltage set up like so: I want to determine how many ohms in load this 2.5V can bear before the TL431 is unable to hold the voltage. I know that this IC requires 500uA to 1mA ...
• 323
2k views

Power cutoff for car when power drops below 13V

I just bought a 2004 Explorer. I have a wireless phone charger and GPS plugged into the cigarette lighter port. The problem is this is always on even when the car is off so I'm forced to unplug ...
• 71
95 views

TL431 output wrong

The purpose of the circuit below is to get a V_cathode of 2.5V (Vref) when VDC is higher than 10.4V approximately. The problem is that when VDC>10.4V the voltage checked in V_cathode is 1.9V ...
206 views

TL431 on-mode voltage

The TL431 datasheet mentions that the VIKA is approximately 2 volts (when the input is more than Vref = 2.5 V), but based on my simulation, it shows me (1.07 V to 1.2 V). I need to know where I can ...
• 319
129 views

Switched power supply output voltage modification

After days of research and experimentation, I was unsuccessful in modifying a power supply output voltage from 15.3V to 5V. My work was focused on the output section of this switched mode power supply,...
• 29
1 vote
66 views

Undervoltage detection using TL431 with high rail voltage

I want to use the circuit below to detect undervoltage at the input. I don't have any other supply but the input voltage, so I should use the input voltage as supply voltage. The problem is that the ...
92 views

How to keep the reference voltage constant for comparator?

I want to build a circuit with a comparator, but the reference voltage is changing (CH3-purple) as seen in the oscilloscope image. I used the TL431 as in the image to keep the reference voltage ...
• 21
373 views

Is this TL431-based overvoltage limiter circuit alright?

I have a supply rail that is 15 V nominally +/- 5%. So the highest nominal voltage is 15.75 V. Due to external fault currents of up to 200 mA, the voltage on this rail can rise anomalously. The fault ...
• 11k
59 views

Can any one explain what type of compensation is this

I will be using the UC3844 controller IC in combination with TL431 to achieve peak current mode control in a 150W forward converter. After some research, I found this schematic on the internet: There ...
• 170
104 views

Using UC3844 and TL431 to compensate a forward converter

I am designing a forward converter capable of providing 5A at 30V at the output. For the compensation part, I am thinking to use UC3844 in combination with TL431 to achieve peak current mode control. ...
• 170
121 views

TLV431 based voltage regulator, possibility of exceeding Vka max. at startup

I need a small (15mA max.) voltage regulator and considering a TLV431 + emitter follower: This works fine but the datasheet states Vka as 7V absolute max. My input voltage Vi however can be as high as ...
• 3,634
1 vote
1k views

flyback converter closed loop by using TL431

I have some things I can't understand when I use a TL431 to compensate for the flyback converter. This picture is from RICHTEK Feedback Control Design of Off-line Flyback Converter. According to this ...
• 409
49 views

TL431 Resistor Choice

I read the Christophe Basoo article The TL431 in Switch-Mode Power Supplies loops: part II About how to choose the resistor I have some questions I would like to ask. On page 13 and page 14 (Watch the ...
• 409
429 views

What's TL431 Output voltage

I am using PSIM to simulate the TL431, and I have some questions. This is my PSIM circuit: When Vref is less than 2.5V, the TL431 doesn't conduct, it looks like an open circuit so Vo is almost 5.1V. ...
• 409
99 views

LED resistor in the TL431

I read the Christophe Basso APEC 2011 seminar, about this figure I have one question. 1.) Why RLED,max need to below this equation(Red line), what happen if RLED above this equation(Red line)
• 409
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TL431 Extracting the Pole

I read the Christophe Basso APEC 2011 seminar, about this figure I have some things I can't get it. 1.)Why should need to put the Cdc capacitor in the circuit, what's this function? to block the DC ...
• 409
77 views

TL431 Type2 Compensator derivation

I am trying to derive the Type 2 Compensator by using TL431, and I read the C.Basso document and I know how to derive the Type 1 Compensator, but I don't know why adding the capacitor (C2) at the Vfb ...
• 409
374 views

TL431 fast lane and slow lane

I read AN_201610_PL16_01 (Using the IRS2982S in a PFC Flyback with opto-isolated feedback) from Infineon. I would like to know what the fast lane and slow lane are. The document doesn't explain it in ...
• 409
104 views

TL431 small signal analysis

I read the Chris Basso APEC 2010 I don't understand why the C1 can connect the Op amp output directly when using the TL431. Because the TL431 output has a BJT.
• 409
1 vote
216 views

TL431 output voltage

Recently, I use the Tl431 to be a regulator, and I want to change the output of TL431. I read the TI datasheet if I want to change the output I need to change the divider resistor, and I also use PSIM ...
• 409
447 views

Is this component in falstad a tl431

I'm self studying electronics, I am now familiarizing myself with the tl431, which is pretty much a "variable zener" aparently. I was shown the following symbol. I would like to simulate ...
510 views

Getting a higher voltage from TL431 in a crowbar circuit

I want to protect a circuit from overvoltage using crowbar circuit, the input voltage shouldn't get above 50 V. TL431 output is 36 V max, can a zener diode in series like schematic below protect the ...
• 2,046
1 vote
240 views

TL431 vs. SMPS transient response

I am currently working with few 150 W SMPS designs for industial applications with heavy transient load condition. Current design works well by mean of line/load regulation and device reliability but ...
696 views

Modifying SMPS power supply to produce a negative voltage

In SMPS power supply that uses a single transistor to generate the switching signal ( no control IC), which component must be modified so the output voltage could be negative? I tried to reverse the ...
287 views

4S Lithium Ion Low Votlage Cutoff

Disclaimer: I'm not an electrical engineer, and most of what I've done so far has been from researching similar designs on the interwebs. I'm just a tinkerer with a soldering iron, so please excuse my ...
1 vote
3k views

LTspice error "could not open Library file" when trying to use TL431 model from TI

I downloaded the LTspice model of TL431 from the Texas Instruments website, but I am not able to simulate the circuit given below due to this error: "could not open Library file" https://www....
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1 vote
99 views

Powering TL431 from MCU output possible?

I'm designing a board with ATmega128 MCU. I have a TL431 reference connected to the ADC_REF pin, with both TL431 and the MCU connected to the same supply, 3.3 V. Now I realized one problem - since ...
• 91
634 views

TL431 Loop Compensation

I'm trying to understand this material from C.Basso regarding TL431 compensation (Designing Compensators for the Control of Switching Power Supplies If you refer to pg.110, there is one example ...
• 357
447 views

TL431 crowbar simulation problem

I'm trying to simulate crowbar circuits, which is mentioned on page 8 of ON SEMI TL431 datasheet (https://www.onsemi.com/pub/Collateral/TL431-D.PDF). I'm using TINA TI for this. There are two circuits,...
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TL431 / TLV431 supercapacitor voltage clamping circuit

I have a question regarding a circuit I've been working on for some time. The circuit is based around existing supercapacitor protection modules and uses a TL431 (actually a TLV431 lower power ...
2k views

Crowbar circuit causes unexpected behavior for op amp circuit

I am using an op amp to amplify an input signal from a microcontroller, which in general is working fine. For over voltage protection, I added the crowbar circuit taken directly from figure 32, page ...
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427 views

I'm trying to build a lipo discharger

The way I want it to work is to slowly discharge the lipo down to storage voltage and then stop. I think the best way to do this is to use a TL431 to control the voltage shutoff and use a power ...
72 views

Ripple in output voltage

I am working on an Active Clamp Forward converter. Schematic is given here: Specs: Output voltage-5V Input voltage 26..42V frequency=500KHz Output power=10W It is working fine in open loop, but in ...
1 vote
445 views

How can I estimate TL431 output voltage swings based on datasheet alone?

I am trying to design a series-pass regulator that brings 12V down to 3.3V. If I see a 20 mA step change in current, I would like to stay within a certain output voltage range (±2%). What parameters ...
• 1,084
1 vote
3k views

TL431 as negative voltage reference

Im building a LM317 based power supply and the output range must be 0.3V-21V. I've used a 2 diodes in series and a resistor supplied by a negative voltage and take the node between resistor and diode ...
• 35
1k views

TL431 Constant Sinking current

A user already asked a question about it at TL431 Constant current source. My SPECIFIC question is about the figure 29. Sure it is not a complete circuit, so I completed it, in order to understand it, ...
2k views

Adjustable current limiting in flyback converter using TL431

I'm building a SMPS and I would like to have a current limiting feature on the output. I'm trying to make a feedback loop using TL431, shunt resistor, optocoupler and a potentiometer, but no luck this ...
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2k views

Voltage Feedback Using TL431

Hello All , In the Above circuit , TL431 is used to regulate the output voltage which is set by resistors RH1 and RL1. resistor RB is bias resistor to provide the current to regulate the output ...
• 103
2k views

Multiplexing PT100 with CD4051

I am interested in developing a generic 8-channel 4-wire PT100 interface for RaspberryPi. Needed accuracy must be better than 1degC and range from 0-200 degC. Additionally i need lead wire ...
1k views

How to use a TL431 for PMOS based reverse polarity protection?

Consider the following illustration: I wonder if it possible to replace the zener with a TL431. The usual application of TL431 supplies specific voltage to next stage but the zener here supplies ...
1 vote
783 views

TL431 LDO series pass transister heating up

I designed a low drop out 5v voltage regulator from 24v input. Works fine. But the series pass transistor heating up more than 100 degree Celsius (with heat sink). Is it normal? Or how to reduce heat? ...
2k views

Strange oscillations with TL431 voltage reference

I have a problem with TL431 voltage reference circuit: There is no load connected to VREF25. When I remove C8, voltage VREF25 is perfectly stable 2.5V. But when I put C8 back into the circuit, ...
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TL431 not tripping at high loads

In the datasheet for TL431, page 26, figure 32, is an example schematic of a crowbar circuit. I've been toying around with this one, since this is the first time I use a TL431. Instead of a TRIAC I ...
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1 vote
4k views

Configuring a TL431 current limitation

I am trying to get this well known circuit [ work inserted in a series of 69 LEDs to protect them according to this specification. Transistor is 2N2222, hfe=18 according to multimeter. The free-...
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Crowbar circuit with TL431 help

So I'm trying to create a OVP using TL431 an a triac, i have checked the datasheet but since i suck at math i don't really get how to set the ref voltage.. datasheet: http://www.ti.com/lit/ds/symlink/...
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19k views

TL431 low battery cut-off

Could somebody please explain the operation of the attached diagram? The circuit was proposed here and here as a low voltage cut-off circuit, which switches off the MOSFET when the voltage drops below ...
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Where should I place the capacitor in this TL431 + TRIAC crowbar circuit?

I'm building a replacement power supply for my C64 and want to add some protection against overvoltage. For that purpose, I tried to find a suitable crowbar circuit that would short-circuit the supply ...
• 587
761 views

Coil-less AC-DC line regulator

I'm trying to fix an AC-DC line regulator that I have build and doesn't work as expected. I'm trying to convert AC 220V mains to DC 5V 10mA without a transformer. To do this I'm using an 1uF 250VAC ...
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