Product Code Database
The Shockley diode (named after William Shockley) is a four-layer semiconductor diode. It is a PNPN diode with alternating layers of P-type and N-type material. It is equivalent to a thyristor with a disconnected gate. Shockley diodes were manufactured and marketed by Shockley Semiconductor Laboratory in the late 1950s. The Shockley diode has a negative resistance characteristic. It was largely superseded by the DIAC.
The Shockley diode remains in an OFF state, with a very high resistance, until a voltage greater than the trigger voltage is applied across its terminals. When the voltage exceeds the trigger value, the resistance drops to an extremely low value and the device switches ON. The constituent transistor help in maintaining the ON and OFF states. Since the construction resembles a pair of interconnected bipolar transistors, one PNP and other NPN, neither transistor can turn ON until the other is turned ON due to the absence of any current through the base-emitter junction. Once sufficient voltage is applied and one of the transistors breaks down, it starts conducting and allows base current to flow through the other transistor, resulting in saturation of both the transistors, keeping both in ON state.
On reducing the voltage to a sufficiently low level, the current flowing becomes insufficient to maintain the transistor bias. Due to insufficient current, one of the transistors will cut off, interrupting the base current to the other transistor, hence sealing both transistors in the OFF state.
Niche applications:
| Switching voltage Vs | 10 V to 250 V | 50 V ± 4 V |
| Holding voltage Vh | 0.5 V to 2 V | 0.8 V |
| Switching current Is | a few μA to some mA | 120 μA |
| Hold current IH | 1 to 50 mA | 14 to 45 mA |
| Reverse current IR | 15 μA | |
| Reverse breakdown voltage Vrb | 10 V to 250 V | 60 V |
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