The Shockley Diode Features & Operation

The Shockey diode is a four layer sandwich of PNPN semiconductor material very similar to the SCR but without a gate as illustrated in the Figure 1.0 below:

Figure 1.0 Shockley or 4-layer diode (PNPN diode)

Figure 1.1 Transistor equivalent of Shockley diode

Figure 1.2 Two transistor equivalent circuit and a symbol of Shockley diode

The Operation of Shockley Diode

A Shockley diode can be turned ON by applying enough voltage between anode and cathode. This voltage will cause one of the transistors to turn ON, which then turns the other transistor ON, ultimately latching both transistors on where they will tend to remain. The two transistors can be turned on OFF again by reducing the applied voltage to a much lower point where there is too small current to maintain transistor bias, at which point one of the transistors will cutoff, which then halts base current through, the other transistor, sealing both transistors in the OFF state as they were before any voltage was applied at all. That is, the Shockley diode tends to stay on once it is turned ON, and stay OFF once it’s turned OFF. There is no in-between or active mode in its operation; it is a purely ON or OFF device like all other thyristors (SCR, diac, triac, etc.)

John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.