Silicon Bidirectional Switch (SBS)

Silicon bidirectional switch SBS (Silicon bidirectional Switch) is also called a bidirectional trigger transistor. It is equivalent to connecting two silicon unidirectional switches in parallel with reverse polarity. The equivalent circuit and symbols are shown in Figure 1. The volt-ampere characteristics and the appearance of a typical product are shown in Figure 2. The forward characteristics and uses of silicon bidirectional switches are the same as silicon unidirectional switches, and the symmetry of the forward and reverse transition voltages is similar to that of bidirectional trigger diodes. The only difference is that the symmetry is better (the deviation is less than 0.2V). The method of using a multimeter to determine gate G is the same as that of a silicon one-way switch and will not be described again. In addition, since the A1 and A2 poles are completely symmetrical in structure, they can no longer be distinguished and can be used interchangeably. The circuit for checking the symmetry of forward and reverse transition voltages is shown in Figure 3. The megohmmeter and multimeter are still used together to measure V (BO) and V (BR) respectively, and finally compare the difference between the two. Example: The silicon bidirectional switch under test is BS08A. Select the R×100 scale of the 500-type multimeter and measure the resistances of ③-② and ①-② to be 820Ω and 830Ω respectively, and they are symmetrical, so it is determined that ② (middle leg) is the gate. According to the circuit shown in Figure 5.9.25, V (BO) = 8.35V and V (BR) = 8.2V were measured respectively. The difference between the two is only 0.15V, which proves that the symmetry is very good.