GK light control thyristor, also known as optical switch, a photosensitive device.
1. The structure of light-control thyristor
SCR usually has three electrodes: control pole G, the anode A and cathode C. The light control thyristor control signal from the light because of its exposure is not necessary to control the most leads, only two electrodes (anode A and cathode C). But its structure and normal SCR, is constituted by the four PNPN device.
Picture this subject as follows:
Thyristor control the shape of light as shown in Figure 1 (a) below. The circuit symbols shown in Figure 1 (b) below.
From the appearance point of view, light control thyristor also by light window, there are two pins and the shell, exactly like the photo diode.
2. The working principle of optical control thyristor
Picture this subject as follows:
the light control with thyristor forward voltage of the anode and cathode with a negative voltage, Figure of the light control thyristor can be equivalent to Figure 2 (b) of the circuit.
Figure to calculate the following formula:
Ia = Il / [1 - (a1 a2)]
Where, Il for the photodiode photocurrent; Ia as a light control thyristor anode current, ie, the output current control thyristor; a1, a2, respectively BGl, BG2 of the current gain.
By the above formula, Ia and Il is proportional to the light when the photodiode current increases, the light control thyristor output current increases accordingly, while Il increases, so BGl, BG2 of the current gain a1 , a2 also increases. When al and a2 of and close to l, Ia light control thyristor maximum, that is fully on. Thyristor light control make the minimum illumination, called the turn-on illumination. Thyristor controlled thyristor with ordinary light, like, once triggered, Serve Communications and Navigation state. As long as the light source of sufficient strength to look at the tube by light window, it immediately became a guide through the state, then light can be maintained even if the withdrawal of turn, unless the increase in the voltage between the anode and cathode is zero, or reversed, in order to close.
3. The characteristics of light control thyristor
To make light control thyristor can be triggered in the faint light turns on, so must make light control thyristor control in a very small current can be reliably turned on. This light control thyristor by the high temperature and pressure constraints, in the current conditions, the same can not be made with ordinary high-power thyristors.
In addition to light control thyristor trigger different, other characteristics of the basic and general thyristor is the same, so the use of thyristors can be selected according to the ordinary, just note that it is light control this feature on the line. Optical wavelength of the light source control thyristors have certain requirements, that is, selectively. Wavelength of 0.8 - 0.9um wavelength infrared and laser around 1um, is an ideal light source controlled thyristor.