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Posted on 25 March 2019

Series and Parallel Connection of Diodes and Thyristors

 

 

 

 

 

 

 

 

 

 

Parallel connection of thyristors

In parallel thyristor circuit arrangements, homogenous current distribution is required from the moment of firing and throughout the entire current flow time. For this purpose, steeply rising trigger pulses of sufficient amplitude, as well as symmetrical line impedances in the main circuit are needed. When connecting thyristors in parallel, it makes sense to arrange them by smallest possible forward voltage difference. To take into account any remaining asymmetry, it is recommended to operate the parallel thyristors with no more than 80 % of the calculated maximum rated value for mean forward current. It may be necessary to limit the rate of rise of current in the individual thyristor using chokes.

Series connection of thyristors

To increase the off-state or blocking voltage, thyristors can be connected in series. Here, even voltage distribution must be ensured - using parallel resistors for blocking and off-state and using parallel RC elements for commutation. The parallel resistors have to be rated such that the current that flows through the resistors is 5…10 times the thyristor off-state current in hot state. To ensure that the thyristor firing is as simultaneous as possible, sufficiently high, steep-rising trigger pulses are required. The voltage load on each thyristor should be at least 10 % lower than for individual operation.

Parallel connection of rectifier diodes

Parallel diode circuits must be as symmetrical as possible in order to achieve even current distribution in the electric circuit (connection point, wiring, and wire length); this will rule out substantial differences in line impedances. It makes sense to arrange parallel diodes by the smallest possible difference in forward losses. To take into account any remaining asymmetry, it is recommended to operate the parallel rectifier diodes with no more than 80% of the calculated maximum rated value for mean forward current.

Series connection of rectifier diodes

To increase the blocking-state voltage, diodes may be connected in series. Especially when "many" diodes are connected in series, in most cases homogenous voltage distribution has to be forced: in blocking-state by using parallel resistors; during commutation using parallel RC. The parallel resistors have to be rated such that the current that flows through the resistors is 5…10 times the diode blocking-state current in hot state. These measures may not be necessary in series connected avalanche diodes. The voltage load on each diode should be at least 10% lower than for individual operation.

 

For more information, please read:

Mounting of Capsule Diodes and Thyristors (disc cells)

Thyristor Basics

Structure and Functional Behavior of PIN Diodes

Criteria for Successful Selection of Diodes and Thyristors

 

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One Response

  1. avatar Priya says:

    need more information about this..

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