Can fast recovery diodes with different withstand voltages be used in series?

Can fast recovery diodes with different withstand voltages be used in series?

It cannot be simply connected in series because the reverse resistance of all fast diodes connected in series must not differ significantly. Otherwise, diodes with high reverse resistance must withstand a greater reverse voltage than other diodes. If they exceed their own withstand voltage, they will be broken down. If irreversible breakdown occurs, it will cause a chain reaction and breakdown one by one. Therefore, the diodes in series must be connected in parallel with voltage sharing resistors. The diodes in the high-voltage silicon stack are screened before being packaged into the silicon stack, and they are produced in the same batch.

Of course, as long as the total withstand voltage after series connection is much higher than the actual voltage, voltage equalization can not be considered because fast recovery diodes are nonlinear devices. Diodes with high reverse resistance will first undergo soft breakdown, and after soft breakdown occurs, the voltage at both ends will no longer rise. However, the current can increase within a small range without secondary breakdown, which is equivalent to reducing the reverse resistance, so the voltage will be redistributed, If two diodes with a withstand voltage of 100 volts are connected in series, the two fast recovery diodes will successively enter a soft breakdown state, and the final withstand voltage is 200 volts. Of course, this is a static state, which is different if it is high-frequency rectification, because diodes in soft breakdown have longer reverse recovery time, greatly increasing power consumption, and are prone to severe heating and damage.

It is possible to use high back pressure s in parallel, as long as the margin is large enough and the performance difference of each diode is not significant, current sharing can also be ignored. For example, if a 2A output is required, five FR107s can be connected in parallel. The reason is also due to the nonlinearity of the diodes, and the forward voltage drop of the diodes with high current will inevitably increase, leading to current splitting to the diodes with low current. When the performance difference is not significant, the diodes will not be damaged.

When reversing, it is necessary to withstand the peak value of the entire voltage. Even if the current is zero, all the voltage is applied to all the diodes. As for equality and inequality, it depends on the respective partial voltage. If the reverse leakage current of some diodes is smaller than that of others, it will withstand a large part of the voltage, while other diodes with high leakage current are equivalent to low resistance, which may cause some fast recovery diodes to breakdown first. This is absolutely not allowed in the fast recovery diodes string or thyristor string in the converter of extra High-voltage direct current, and it is not like someone said that voltage balancing resistance is not allowed.