TI 2N4988

The GE/RCA 2N4987 through -90 Silicon Unilateral Switches (SUS) are planar monolithic silicon integrated circuits whose thyristor electrical characteristics closely approximate those of an "ideal" four-layer diode. The devices are designed to switch at 8V with a temperature coefficient of 0.02%/°C. A gate lead is provided to eliminate rate effects, obtain triggering information at lower voltages, and achieve transient-free waveforms. The Silicon Unilateral Switches are designed and characterized for monostable and bistable applications where low cost is critical. These types are available in the JEDEC TO-98 package. Devices in the TO-98 package are available with and without a mounting flange (see dimensional drawing).

• Silicon Controlled Rectifier (SCR) trigger
• Frequency driver
• Ring counter
• Crosspoint switch
• Overvoltage sensor
• Fewer components than transistor flip-flop, "B" output free of transient waveforms
• Switching action of 2N4990 allows smaller capacitors while achieving reliable thyristor triggering
• Utilizes energy stored in capacitor to generate fast rise or fall times
• For overvoltage, SCR conducts and blows fuse; for fast-rising voltage, circuit triggers between 13.2V and 14V; for slow-rising voltage, circuit triggers between 14V and 17V
• Capacitor charges until switching voltage is reached. When the SUS conducts, the inductor causes the current to oscillate. When current through the SUS falls below holding current, device turns off and cycle repeats
• Eliminates spike at center of sawtooth wave via gate triggering
• Sawtooth output frequency of each stage is half that of the preceding stage