* Question
| What is the role of the parallel RC network at both ends of the thyristor? |
* Answer
| We know that the thyristor has an important characteristic parameter – the critical state of the off-state voltage rise rate dlv / dlt.It indicates the minimum voltage rise rate of the thyristor from the off state to the on state at rated junction temperature and gate open conditions.In the thyristor circuit, an RC series network is connected in parallel at both ends thereof, and the network is often referred to as an RC RC absorption circuit.When the thyristor is in a blocking state, the J2 junction surface is equivalent to a capacitor C0 because the layers are closely spaced.If the thyristor voltage is rising too fast when the thyristor is turned off, the larger the charging current of C0, the more likely the gate will be mis-conducted without the trigger signal, which is often said to be hard-on. This isnot allowed.Therefore, there should be a certain limit on the rate of rise of the anode voltage applied to the thyristor.Because the circuit always has inductance (transformer leakage inductance or load inductance), the series resistance R with the capacitor C can act as a damping function, which can prevent the R, L, C circuits from appearing at the ends of the capacitor during the transition process.Overvoltage damages the thyristor. |
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