CS243553B1 - A method of measuring the time stability of a semiconductor diode closing current at elevated temperature - Google Patents

Abstract

The method of measuring the time stability of the closing current of diodes at elevated temperature solves the problem of measuring the electrical parameters of discrete semiconductor components. Time stability of the closing current is important from the point of view of long-term reliable operation of semiconductor diodes. It is of great importance especially in cases where work is carried out at an upper limit temperature and with a small reserve of final energy. Monitoring the temporal stability of the closing current, i.e. the dependence of IK = f(t) at a constant closing voltage is time-consuming and unsuitable for serial production. The method of measurement according to the invention allows to evaluate the temporal stability of the closing current in a short time, about 5 seconds. It is suitable for serial production and can also be used for automatic evaluation. The main area of application of this method of measurement is for rectifier diodes, fast rectifier diodes, high-voltage rectifiers, but it is also possible to apply it for transistors

Description

SUMMARY OF THE INVENTION The present invention is directed to a method for measuring the stability of a closed-circuit current of a semiconductor diode at elevated temperature.

The blocking capability of semiconductor diodes in the downstream direction is determined by the long-term stability of the closing current. In addition to the closing voltage, the decisive parameter for the closing current value is the temperature. In an ideal diode, the closing current through the semiconductor volume is given by the so-called saturation current Io, whose temperature dependence is given by: Io (T) = Io (To) e »(T —To) (1) where

To = 298 K (normal temperature) T> To - increased temperature and - coefficient (for Si = 0.1 K'1) In fact, the closing current is higher than that of the first relation and is caused mainly by undefined surface states. Accordingly, the nature of the temperature and time dependence of the closing current may be varied. The current method of measuring the closing current stability is very cumbersome. The diode is placed in a thermostat heated to elevated temperature and the shut-off current value is monitored for a few minutes to several hours. Therefore, this method is not suitable for mass production.

The aforementioned drawback removes the method of measurement according to the invention, the principle of which is that the diode is heated to an elevated temperature and long-term time stability is evaluated on a natural cooling diode by measuring at least two closing current values measured at constant closing voltage, which are measured in a short time sequence behind.

The method of measurement according to the invention can be done, for example, as follows:

The diode heats up to an elevated temperature in the thermostate or by passing a defined pass current pulse. In order to increase the sensitivity, it is appropriate in the sense of the relation (1) to choose a temperature close to the maximum permissible transition temperature. Thereafter, the diode is quickly removed from the thermostat or the heating through current is interrupted and a specific closing voltage is applied.

The time from the interruption of the heating to the connection of the closing voltage is a maximum of 2 seconds. The initial value of the closing current IR0 is subtracted and after the time i t the second value IRi.

As satisfactory diodes for the long-term stability of the closing current, such diodes are evaluated in which the decrease of the closing current as a function of time corresponds to the natural cooling of the diode - the courses 1 and 2 in figure 1, the course 1 corresponds to a diode with a smaller thermal capacity.

The diodes in which the drop of the closing current is insignificant - the course 3 in FIG. 1, or the current rising - the course 4 in FIG. 1 is judged to be unsatisfactory.

A time dut = ti - to = 1- ^ 3 seconds is sufficient for such a rating of the closing current stability. Also unsatisfactory are the diodes in which the value of the leakage current IK0, determined for a particular diode type and temperature, is also evaluated.

This method of measuring the long-term stability of the diode closing current is suitable for measuring medium power rectifier diodes both conventional and fast, and for high voltage rectifiers that can be measured in a normal environment. It can also be used to measure the time stability of transistor residual currents.

Claims (2)

SUBJECT 1. A method of measuring the temporal stability of the reverse current of semiconductor diodes at elevated temperature, characterized in that the diode is heated to an elevated temperature and the long term stability is evaluated on a naturally cooling diode by measuring at least two reverse current measured values. Max. 3 seconds in a row. 2. A measurement method as in 1, characterized in that the diode is heated to an elevated temperature by a defined current pulse in the forward direction.