Connect diodes in series to improve voltage withstand

 

§01 strand Coupled diode

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One 、 Source of problem

   Diodes used at high voltage ,  If the withstand voltage is not enough ,  Its reverse breakdown voltage can be increased by series .  Some people according to the series capacitance Use of uniform resistance is required ,  For diodes connected in series, it is also through the voltage equalizing resistor To improve the reliability of series diode withstand voltage .  The problem is coming. , Do you need this voltage equalizing resistor for series diodes ？

  
   This is the forward conduction voltage current characteristic curve of ordinary headphones ,  The inverse current drawn here is exaggerated , It should be very .  If the reverse voltage exceeds a certain threshold ,  The reverse current will increase sharply ,  This voltage threshold is the reverse breakdown voltage of the diode .

  
   Although the diode VA Characteristics are not linear ,  But his change is to meet the positive impedance characteristic ,  Showing a monotonous trend .  For multiple diodes in series ,   The final breakdown voltage should be the sum of their breakdown voltages .   So for the so-called uniform resistance ,  It should be unnecessary .  On this point , Let's verify it through experiments .

  

Two 、 Measure the series diode

1、 diode FR107

   The diode under test is just from TB Buy to FR107 1A/1000V diode .  according to FR107 Data manual ,  You can see two parameters that characterize his response speed .  One is PN Junction capacitance , And 15pF,  The other is recovery time , Less than 500ns. FR107 The reverse withstand voltage of is less than 1000V.

  

2、 Measurement results

   Use a multimeter to measure the forward conduction voltage of the diode ,  Use high-voltage power supply and its voltage dividing circuit to measure Output high voltage and output current .  These are the two diodes to be measured , In series .  Next, measure their forward voltage and reverse voltage respectively .  The forward voltage is not much different , All in 0.53V about .  When measuring the reverse voltage , It is when the reverse current is 10 Measure under microampere . D1 The reverse breakdown voltage of is 1464V,D2 The reverse breakdown voltage of is 1273V.  The reverse breakdown voltage of the two in series is 2776V.  You can see that it is within the error range , The reverse breakdown voltage in series is equal to The sum of their respective reverse breakdown voltages .

  
   Next, measure the reverse breakdown voltage of three diodes in series . The reverse breakdown voltage of the first two diodes has been measured .  The reverse breakdown voltage of the third diode is 1475V.  What is the reverse breakdown voltage after they are connected in series ？  The measurement result is 4354V.  This value is slightly larger than the sum of their reverse breakdown voltage .

  
 

※ junction    On ※

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   through Experiments have shown ,  For the application of series diode to improve reverse breakdown voltage ,  In fact, there is no need to use voltage sharing resistors in parallel .  This is different from the series capacitor to improve the withstand voltage .

  

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