Dynamic parameters of thyristor and three derivative devices

Dynamic parameters of thyristor and three derivative devices

Dynamic parameters

In addition to the turn-on time and turn-off time, there are the following two parameters:

(1) The critical rate of rise of off-state voltage du/dt

The critical off-state voltage rise rate refers to the maximum rise rate of the applied voltage that will not cause the thyristor to switch from off-state to on-state under the conditions of rated junction temperature and open gate. If the voltage applied across the blocked thyristor has a positive rate of rise, it is equivalent to a charging current flowing through the J2 junction of a capacitor in the blocking state, which is called a displacement current. When this current flows through the J3 junction, it will act like a gate trigger current.

If the voltage rise rate is too large and the charging current is large enough, the thyristor will be turned on by mistake. Therefore, the actual voltage rise rate in use must be lower than this critical value.

2) The critical rate of rise of the on-state current di/dt

The critical rise rate of on-state current refers to the maximum on-state current rise rate that the thyristor can withstand from blocking to conducting under specified conditions and normal gate drive.

If the current rises too fast, as soon as the thyristor is turned on, a large current will be concentrated in a small area near the gate, which will cause local overheating and damage the thyristor.

Fast thyristor

The working principle of Fast Switching Thyristor (FST) is the same as that of ordinary thyristor. The off time of ordinary thyristor is generally hundreds of microseconds, that of fast thyristor is tens of microseconds, and that of high-frequency thyristor is 10 μ S, which can be applied to chopper or inverter circuits above 400Hz and 40KHz respectively. Due to the improvement of the core structure and manufacturing process of the ordinary thyristor, the switching time of the fast thyristor and the tolerance of du/dt and di/dt have been significantly improved. Compared with ordinary thyristors, high-frequency thyristors have lower voltage and current ratings. Due to the high operating frequency, when selecting the average on-state current of fast thyristors and high-frequency thyristors, the heating effect of their switching consumption should be considered.

Reverse conducting thyristor

Reverse Conducting Thyristor (RCT) is a power integrated device made of ordinary thyristor and anti-parallel diode on the same die. This kind of device does not have the ability to withstand reverse voltage. Once withstand the reverse voltage, the anti-parallel diode is turned on. The graphical symbols and volt-ampere characteristics of the reverse conducting thyristor are shown in Figure 1. Because the reverse conducting thyristor is different from the special structure of the ordinary thyristor, it has excellent performance such as high voltage resistance, low on-state voltage, short turn-off time, good high temperature characteristics and high rated junction temperature, and can be used in circuits that do not need to block reverse voltage.

Dynamic parameters of thyristor and three derivative devices
Figure 1 – Graphical symbols and volt-ampere characteristics of reverse conducting thyristors

Light-controlled thyristor

Light Triggered Thyristor (LTT), also known as light-triggered thyristor, is a thyristor that uses a certain wavelength of light signal to trigger the conduction. The graphic symbols and volt-ampere characteristics of the light-controlled thyristor are shown in Figure 2. The light intensity is different, the turning voltage is also different, the turning voltage decreases with the increase of light intensity.

The low-power light-controlled thyristor has only two terminals, the anode and the cathode, while the high-power light-controlled thyristor also has an optical cable, which is equipped with a light-emitting diode or a semiconductor laser as a trigger light source. Since the use of light triggering ensures the insulation between the main circuit and the control circuit, and can avoid the influence of electromagnetic interference, the light-controlled thyristor is currently used in high-voltage and high-power applications, such as high-voltage direct current transmission and high-voltage nuclear fusion devices have extremely wide applications.

Dynamic parameters of thyristor and three derivative devices
Figure 2 – Graphical symbols and volt-ampere characteristics of light-controlled thyristors