SBS – Silicon Bidirectional Switch

The SBS – Silicon Bidirectional Switch is a symmetrical low power device used on trigger applications. The SBS is more versatile than the SIDAC. It also has an additional terminal (gate or G), which allows you to modify its trigger characteristics with small pulses of current (tens of microamperes (uA)).

Its low cost, high speed and ability to trigger thyristor gates with high current values makes this device very useful in many applications. Silicon Bidirectional Switch is not only an improved version of the four-layer diode, but is manufactured as an integrated circuit consisting of transistors, diodes and resistors.

• Diagram (a) shows its symbol
• Diagram (b) shows the structure at circuit level, and …
• Diagram (c) shows its I-V characteristics.

The Motorola MBS4991 is a typical example of a symmetrical Silicon Bidirectional Switch.

SBS main characteristics

Its main characteristic parameters according to diagram (c) are:

• Switching voltage V = 8 V (VS1).
• Switching current I = 175uA (IS1).
• Holding current I = 0.7mA (IH1).
• ON state forward voltage V = 1.4 V (VF1).

To trigger this device it is necessary to exceed the switching voltage V = 8 volts (VS1) or to apply a gate current I = 200uA. (IS1).