In this post we learn how a shunt regulator IC works typically in SMPS circuits. We take the example of the popular TL431 device and try to understand its use in electronic circuits through a few of its application notes.
Electrical Specifications
Technically the deviceTL431简单地称为可编程调节器，可以理解为可调式二极管。
Let's learn more about its specifications and application notes.
TL431归因于以下主要功能：
- Output voltage settable or programmable from 2.5V (minimum reference) up to 36 volts.
- 输出阻抗低动态性，约为0.2欧姆。
- Sink current handling capacity up to maximum 100mA
- Unlike normal zeners, noise generation is negligible.
- Switching response lightning fast.
IC TL431如何工作？
The TL431 is a three pin transistor like (such as BC547) adjustable or programmable voltage regulator.
输出电压可以使用设备的指定销钉外只有两个电阻来尺寸。
下图显示了设备的内部框图以及引脚输出名称。
下图指示实际设备的销钉出现。让我们看看如何将该设备配置为实用电路。
使用TL431的电路示例
The circuit below shows how the above device TL431 can be used as a typical shunt regulator.
上图显示了如何在几个电阻的帮助下，可以将TL431作为分流器调节器连接起来，以生成2.5V至36V之间的输出。R1是可变电阻器，用于调整输出电压。
可以使用欧姆定律来计算供应的串联电阻阳性输入：
R = Vi / I = Vi / 0.1
在这里，VI是必须低于35 V的电源输入。0.1或100 mA是IC的最大分流电流规范，R是欧姆中的电阻器。
Calculating Shunt Regulator Resistors
The following formula holds good for acquiring the values of the various components used for fixing the shunt voltage.
Vo = (1 + R1/R2)Vref
In case a 78XX needs to be used in conjunction with the device, the following circuit can be used:
TL431阴极的地面与78xx的地面引脚相连。来自78xx IC的输出与确定输出电压的潜在分隔网络连接。
The parts can be identified through the formula shown in the diagram.
上面的配置仅限于输出处的最大100 mA电流。为了获得更高的电流，可以使用晶体管缓冲液，如以下电路所示。
In the above diagram most of the parts placement is similar to the first shunt regulator design, except that here the cathode is provided with a resistor to positive and the point also becomes the base trigger of the connected buffer transistor.
The output current will depend on the magnitude of current the transistor is able to sink.
在上图中，我们可以看到两个不提及值的电阻，一个与输入电源线串联，另一个在PNP晶体管的底部。
The resistor at the input side limits the maximum tolerable current that can be sinked or shunted by the PNP transistor. This can be calculated in the same way as discussed previously for the first TL431 regulator diagram. This resistor protects the transistor from burning due to short circuit at the output.
The resistor at the base of the transistor is not critical and may arbitrarily selected anything between 1k and 4k7.
Application Areas of the IC TL431
Although the above configurations can be used in any place where precision voltage setting and references may be required, it's extensively used in SMPS circuits nowadays for generating precise reference voltage for the connected opto coupler, which in turn prompts the input mosfet of the SMPS to regulate the output voltage precisely to the desired levels.
For more info please go tohttps://www.fairchildsemi.com/ds/TL/TL431A.pdf
You are welcome!
Great article!
谢谢you. Was very helpful.
you are welcome
can also use 2N3819
Can also use 2N3819
where?
我从链接的数据表中复制了它，它仍然显示相同的数据。
yes it makes sense…any voltage drop in series with a 78XX ground pin adds up with the output result.
how TL431 can be used from 1 volt to higher voltages as ref. pl. help me.
Do you mean from minimum 1V input, Sorry it won’t work with a 1V input supply
亲爱的斯瓦加瑟姆，
I think Mr.Devdatt is asking about Reference voltage. TLV431 has a low Ref.voltage of 1.25V . (TL431’s reference voltage is 2.5V)
实际上，我来这里问一个疑问。
电路（TL431 + 7805）显示了在输出和接地之间连接的R1和R2。但是在某些电路中，我已经看到R1和R2在输入和地面之间连接。
是there any difference/advantage between these two type of connections.
谢谢
Dear Anil,
For the 7805 circuit, taking the reference from the output makes more sense because the output is more stabilized than the input. Once the output is set using the preset, there’s virtually no chance for the reference to change, and therefore it’s more reliable to use R1/R2 at the output side.
Hi Swag
这是一个最有用的网站 - 谢谢。
I’m wondering how to make a BMS to control charging and discharging a battery made up of LTO cells connected as 5S to give me approximately 12V.
I found something I hope can be easily modified at homemade-circuits.com/wp-content/uploads/2019/10/5.jpg but this will only top balance and I don’t understand how to select the resistor values to make the cut-off 2.75V.
谢谢for any help and advice you are able to offer
谢谢Tim,
You can use the following set up and adjust the preset accordingly for each module separately:
//m.addme-blog.com/wp-content/uploads/2019/10/5-1.jpg
Good day Swag, how can I modify this circuit for 12v, 10A output. Thanks.
Hi Adeymei, you can do it by replacing the transistor in the last circuit with a 20 amp transistor
Hello Swagatam:
You mentioned that this device can goto 36 volt…I want to build a 36 volt supply to charge a 36 volt lithium iron phosphate pack. I have a 36 volt transformer, bridge rectifier, caps, tl431’s, and NPN power transistors rated at 60 Volt… i.e 2n3055. i am assuming I need to make the power circuit with a darlington configuration to drive the 2n3055 type.
Can you recommend using the tl431 at this upper voltage, or use a fixed zener?
Many thanks for your work.
Hello Lisa, a shunt regulator is not recommended for a transformer based supply, it is recommended for alternators or generators. Instead you can use a simple emitter follower circuit for charging your bats. as given below
Hello Swagatam..
I guess I was over thinking this… I will make this up and test it…
Thank You..
OK, no problem!
请就您的评论，我想询问基于TRAFO的充电器，交流发电机和发电机之间的区别，因为Trafo会影响分流器调节器。
我有used emitter follower system but it doesn’t regulate well as it shoots above level.
我有tried tl431 shunt regulator but for high voltage/current, 15v, 10amps, the tl431 gets very hot and burns without any negative effect on the transistor Please help to resolve these issues. Thanks Swag
对于基于TRAFO的充电器，最好选择正常的线性电压调节器（例如LM338等），对于交流发电机，可以使用分流器调节器，因为它可以防止交流发电机线圈中的高压升高，并且还可以保持其控制频率，但是对于Trafo，这可能会导致这可能导致这可能导致这可能导致此导致TRAFO的频率加热trafo。
Please where will I put the 12v regulator for the tl431 in the circuit. Thanks sir.
ADEYEMI，如果正确计算了参数，则实际上永远不会燃烧。其次，如果正确安装了齐纳二极管，则发射器追随者也将永远不会更改输出。再次检查您的电路。
You can refer to the following article for more variations:
//m.addme-blog.com/simple-voltage-regulator-circuits-using-transistor-and-zener-diode/
非常感谢Swagatam响应。我有tried few of transistor-zener regulators but I still prefer tl431 shunt regulator. It worked well for me in regulation but just that it got burnt as it can sustain at high voltage-current. Please help me out in getting the parameters right. Thanks
Adeyemi，最后一个电路是高电流的理想分流电路，您必须根据要求计算参数。必须对晶体管进行适当的额定额定值以沉降过多的电压。
r =（vi - 0.6）HFE / LOAD电流，用于15.5V输入和10AMP载荷电流，请为晶体管底座的R r r。请帮助计算参数。谢谢
实际上，由于BJT是PNP，因此最后一个电路中的基本电阻不是BJT的偏置电阻。这只是为了确保BJT基数只要输入供应量低于最大阈值，就可以将BJT基数保持在正开关状态。
You just have to calculate the other things in the circuit as explained through the various diagrams.
hi, what is the circuit efficiency? I want to use this as a powerbank, 2 lipo batteries. And also for power suppy charging 12v car batteries.
Efficiency is not relevant for this circuit since it is supposed to shunt and dissipate the excess power. If it is used for charging battery then the recommended source should be an alternator.
请您提供基于OPAMP的分流器调节器
The left side op amp stage is the op amp shunt regulator in the following schematic
//m.addme-blog.com/solar-water-heater-with-battery-charger/