Basic characteristics of TL431 and oscillator circuit

 

§01TL431基本特性

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一、基本介绍

  TL431It is a more commonly used reference power supply, It can form very flexible and changeable circuits. There are many related applications. The following is a preliminary test of its basic characteristics.

  

二、Multimeter test pins

  The diode gear of the multimeter is used below, 测试一下TL431turn-on voltage between pins. 对照TL431的数据手册, The diode conduction characteristics between the corresponding pins are respectively measured, The anode-to-cathode turn-on voltage is 0.602V,This corresponds to the forward voltage of the silicon diode. 反向截止. between the reference pole and the anode,正向导通电压为1.774V, The reverse conduction voltage is 1.358V. between the reference electrode and the cathode0.817V. 反向截止.

  
  利用这个关系, can help us determine quicklyTL431Definition of each pin.

  

三、基本特性测试

  Build the basic test circuit below, 测试一下TL431的基本特性. This is the test circuit, 测量TL431The voltage between the cathode and anode is 2.491V.

  
  Next, use a networked multimeter, and a digitally programmable DC power supplyDH1766, Measure the input voltage, relationship with the regulated voltage. 最后, Plot the relationship between the two.

  
  这是测量结果,  可以看到当输入电压超过2.5V之后,The output starts to regulate. If the voltage of the regulation stage is plotted separately, It can be seen that it increases with the input voltage,That is, flow throughTL431increase in current,TL431voltage also from2.484V增加到2.4859V. Consider the series resistance of 300欧姆, 所以可以计算出TL431The equivalent resistance of 0.255欧姆. This is consistent with the data in the data sheet.

  

四、振荡电路

  根据TL431内部结构,It can be seen that it has a signal reverse amplification function between the reference terminal and the negative pole. So directly connecting the reference terminal from the cathode can keep the circuit stable. If a phase shift circuit is introduced in this link, Such as the resistance-capacitance phase-shift circuit,Then it is possible to form an oscillation circuit. A basis is given hereTL431phase-shift oscillator circuit, It consists of two levelsRC移相, This will maximize production180度的相移. Thereby, an oscillating output can be generated.

  
  This is an oscillator circuit built on a breadboard. This is measuredTL431Oscillating waveform on the cathode, 振荡频率为2.23kHz. 这是一个有趣的实验, Also verified to useTL431Possibility to build oscillators.
  
 

※ 总  结 ※

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  本The text is measuredTL431的基本特性, Summarized the use of multimeter diode gear measurementTL431管脚功能. Tested with adjustable power supplyTL431voltage regulation characteristics and internal resistance. 最后利 用RCPhase shifting makes an interesting oscillator circuit.

  

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