The influence of temperature on the working characteristics of thyristor

Semiconductor single crystal silicon is very sensitive to changes in ambient temperature, for example, its resistivity changes with temperature changes. When monocrystalline silicon is made into a thyristor, the parameters of the thyristor also change with temperature. Although the thyristor can work normally in a wide temperature range, its parameters have indeed changed.

The influence of temperature on the changes of thyristor parameters is regular. Mastering this law can improve the initiative when selecting thyristors suitable for their circuit characteristics; second, the cause of failure can be found in time in the application, because the thyristor that violates this law should It is a defective product.

1. The influence of temperature on the forward and reverse withstand voltage and leakage current

As the ambient temperature increases, the forward and reverse withstand voltage of the thyristor, that is, the breakdown voltage will increase, and the leakage current will increase, see (Figure 1). If the temperature increases and the withstand voltage decreases, it should be a "defective product". The leakage current increases greatly with the increase of temperature. When the junction temperature is 125°C, it is about a hundred times higher than that at room temperature. For example, the leakage current of a certain specification of thyristor at room temperature is 0.05 mA, and it reaches dozens of mA or even at 125°C. An order of magnitude greater.

Figure 1 The relationship between temperature and reverse withstand voltage and leakage current

2. The influence of temperature on gate trigger current

When the thyristor works at an allowable junction temperature of 125°C, it is called a high temperature state. At this time, the leakage current increases, plus

The lifetime of minority carriers in the PN junction increases as the temperature increases, and the amplification factor increases accordingly. These two points cause the gate trigger current to decrease as the temperature rises, and when it works at a high temperature, it is much smaller than that at room temperature. In order to avoid false triggering caused by too small trigger power, the standard stipulates "non-trigger voltage", "non-trigger current" and other items. The thyristor can only be triggered when the value is greater than this value, otherwise it is unqualified. It should be noted that when leaving the factory, the gate current is the measured value at room temperature and the anode voltage is 6V. In practical use, it is high temperature and high pressure. At this time, it is easy to trigger conduction because the trigger current becomes smaller.

3. The influence of temperature on switching time

The switching time includes two times of turn-on and turn-off. Temperature has little effect on the turn-on time, but has a great effect on the turn-off time, as shown in (Figure 2). Therefore, the standard stipulates that the off-time measurement must be performed under high temperature conditions. The turn-off time of the high temperature test is 1.5 to 2 times longer than that of the room temperature test. When it is turned on, the “minority carriers” that carry electric charges are accumulated on both sides of the PN junction. The turn-off process is a process in which the charge disappears. This time is called the “off time”, which is related to the “minority carrier lifetime”. "related. The lifetime of the minority carrier increases with the increase of temperature, the accumulated electric charge disappears more difficultly, the turn-off process is lengthened, and the "turn-off time" increases.

Figure 2 The relationship between temperature and turn-off time

Fourth. the influence of temperature on dv/dt

In the circuit, too high dv/dt will cause the thyristor to turn on. The ability of the thyristor to withstand dv/dt with a small trigger current is correspondingly weak. Similarly, the trigger current becomes smaller when the temperature rises, and the dv/dt capability of the thyristor decreases accordingly. The standard stipulates that the thyristor must be tested for dv/dt under high temperature conditions.

Figure 3 The relationship between the maintenance current and the temperature

5. The influence of temperature on maintaining current

The maintenance current is a function of temperature. It decreases with the increase of temperature, and the magnitude of the change is larger. The user should give full consideration when using it, see (Figure 3). The maintenance current provided by the factory is measured at room temperature.

Sixth. the influence of temperature on the on-state characteristics

The on-state voltage drop of the thyristor decreases when the temperature increases. People use this characteristic of the thyristor to conduct a "junction temperature" test. First find out the relationship curve between the temperature and the on-state voltage drop of a certain thyristor. On the contrary, by measuring the on-state voltage drop of this kind of thyristor during operation, the corresponding temperature value can be found on the relationship curve, and this temperature is the chip junction temperature at this time.

The source of this article refers to the Power Electronics Industry Network