Overload on a Thyristor Caused by a Single Large-Amplitude Current Pulse

Abstract

Overloading a thyristor with a single sinusoidal current pulse is considered. The current-voltage characteristic of the thyristor is approximated by the expression V = V₀ + IR. Heat conduction equations are solved making some simplifying assumptions. The temperature rise in a silicon plate is determined during and after the passage of a current pulse through the systems W-Si-W, Cu-Si-Cu, and W-Si-Cu. In particular, the temperature rise at the Si-W boundary at the end of a 10 msec sinusoidal current pulse is given by the following expression, which applies to the W-Si-W system (silicon plate 0.4 mm thick and tungsten heat sink ≥1 mm thick):

$$ {\text{T/P }}_{\text{m}} {\text{ = 0}}{\text{.01025 + 0}}{\text{.0034V}}_{\text{0}} {\text{/V }}_{\text{m}} $$

where V _m = V₀ + I_mR and P _m = I_mV_m are the peak values of the voltage and power during this pulse. The temperature rise in the Cu-Si-Cu system is approximately half that given above, other conditions being equal. The temperature in the central plane of the silicon plate during the passage of a cur — rent pulse differs considerably from the temperature at the boundaries of this plate, but at the end of the pulse (for a plate 0.4 mm thick and a pulse 10 msec long) the temperature throughout the plate is practically the same. An experimental determination was made of the temperature rise in a silicon plate at the end of a pulse. The temperature dependence of the forward voltage drop at low current densities (~30 mA/cm²) is used as the temperature-sensitive parameter. The experimental results are in satisfactory agreement with the theoretical formulas.