Ri In Sik, a researcher at the Semi-conductor Institute, made an analysis of reverse voltage distribution of high-voltage diode stack considering the effect of temperature.
First, he presented an equivalent circuit of a high–voltage silicon diode taking into account the effects of temperature and reverse voltage, and obtained an analytical expression for impedance of a diode. Then, he proposed the most generalized equivalent circuit of a high–voltage diode stack consisting of a serial connection of several diodes, and obtained an analytical expression for the reverse voltage applied to each diode. As a result, he offered an easy estimation of the reverse voltage distribution of a high–voltage diode stack by an analytical method, not in an experimental way.
High–voltage diode stacks (HVDS) are now widely used in extracorporeal shock wave lithotriptors, diagnostic X–ray equipment, sound detectors, night glasses, high–voltage magnetic compression modulators, high–voltage pulse generators, dust collectors and electrostatic fly–ash separators at thermal power plants.
The most important characteristic of an HVDS is reverse voltage distribution between chips or diodes. If the non–uniformity of reverse voltage distribution is severe, twice the breakdown voltage of P–N junction or more can be applied to the chips or diodes placed on high–voltage terminal and ground terminal, leading to their destructions. The reverse voltage distribution of an HVDS is mainly affected by the characteristics of chips or diodes, such as the dependence of the temperature and the reverse voltage on the impedance of them. The dependence of impedances of chips or diodes on temperature and reverse voltage strongly affect the reverse voltage distribution of an HVDS. Also, according to an HVDS consisting of stacked chips or a serial connection of individual diodes, the leakage impedances connected to the high–voltage terminal and the ground terminal are varied and they strongly affect the reverse voltage distribution. The stacking of chips and a serial connection of the individual diodes are the technologies that have been widely used to manufacture HVDS.
The reverse current of the diode increases and its barrier resistance decreases with increasing temperature and reverse voltage. In addition, when the reverse voltage of the diode increases, the width of the space–charge layer increases, thus the barrier resistance decreases. Consequently, the impedance of the diode decreases with increasing temperature and reverse voltage. Hence, the equivalent circuit of an HVDS consisting of a serial connection of the individual diodes is needed in order to analyze the reverse voltage distribution of it, considering the effects of the temperature and the reverse voltage of the diodes.
That is why, he proposed and analyzed a new equivalent circuit of an HVDS, including not only the impedance and the uniform voltage impedance of each device, but also the leakage impedance connected to the high–voltage terminal and the ground terminal.
The calculated values of the reverse voltage distribution of a high–voltage diode stack were shown to be in good agreement with the measured values.
His essay “Analysis of Reverse Voltage Distribution of High–Voltage Diode Stack Considering Effect of Temperature” is carried in SCI Journal “Solid-State Electronics”.
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