Construction and Operation
amounts of current because of the low voltage drop (VT) across the device. Once the
current flowing through the device is either interrupted or falls below a minimum holding
current (IH), the SIDACtor resets, returning to its off state. If the IPP rating is exceeded, the
SIDACtor device typically becomes a permanent short circuit.
Physics
The SIDACtor device is a semiconductor device which is characterized as having four
layers of alternating conductivity: PNPN. (Figure 5.2) The four layers include an emitter
layer, an upper base layer, a mid-region layer, and a lower base layer. The emitter is
sometimes referred to as a cathode region, with the lower base layer being referred to as
an anode region.
As the voltage across the SIDACtor device increases and exceeds the device’s VDRM, the
electric field across the center junction reaches a value sufficient to cause avalanche
multiplication. As avalanche multiplication occurs, the impedance of the device begins to
decrease, and current flow begins to increase until the SIDACtor device’s current gain
exceeds unity. Once unity is exceeded, the SIDACtor device switches from a high
impedance (measured at VS) to a low impedance (measured at VT) until the current flowing
through the device is reduced below its holding current (IH).
N
P
N
P
N
Figure 5.2 Geometric Structure of Bidirectional SIDACtor devices
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SIDACtor Data Book and Design Guide
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