Application of American CDE capacitor module in buffer circuit

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Application of American CDE capacitor module in buffer circuit [Copy link]

Application of American CDE capacitor module in buffer circuit

As we all know, in the application circuit of power electronic devices, a snubber circuit, that is, an absorption circuit, must be set without exception. Some readers who are using fully controlled devices for the first time may have such a feeling: the device is inexplicably damaged. Although there are many reasons for damage, improper selection of snubber circuits and snubber capacitors is an important reason that cannot be ignored.

Device damage is nothing more than the device being damaged by excessive di/dt, dv/dt or instantaneous power consumption during the switching process. The role of the snubber circuit is to change the switching trajectory of the device, control various transient overvoltages, reduce device switching losses, and protect the safe operation of the device.

Figure 1 shows the switching waveform when the GTR drives an inductive load. It is not difficult to see that during the turn-on and turn-off process, the GTR collector voltage uc and collector current ic will appear at the same time, resulting in large switching power consumption. By adding a buffer circuit, part of the switching power consumption can be transferred to the buffer circuit, thereby ensuring the safe operation of the device.

A typical composite snubber circuit is shown in Figure 2. When the GTR is turned off, the load current charges the snubber capacitor Cs through the snubber diode D, and the collector current ic gradually decreases. Since the voltage across the capacitor Cs cannot change suddenly, the GTR collector voltage rise rate dv/dt is effectively limited, reducing the voltage stress of the GTR. At the same time, the collector current is transferred to the snubber circuit, thereby reducing the shutdown power consumption. The energy LI2/2 stored in the GTR collector bus inductance and stray inductance when the GTR is turned on is converted into CsVcs2/2 and stored in the snubber capacitor Cs. When the GTR is turned on, the collector bus inductance and other stray inductances and the current limiting effect of Rs on the discharge of Cs effectively limit the GTR collector current rise rate di/dt, reducing the current stress of the GTR, and also reducing the turn-on power consumption. In this way, the snubber circuit not only reduces the switching loss of the switching device, but also reduces the voltage and current stress borne by the device, thereby protecting the safe operation of the GTR.