The Shockley diode is a four-layer semiconductor device invented by William Shockley. It consists of three PN junctions (J1, J2, J3) constructed by connecting two transistors. In the forward bias state, J1 and J3 are forward biased while J2 is reverse biased, allowing current to flow. In reverse bias, J1 and J3 are reverse biased while J2 is forward biased, blocking current flow. The diode acts as a closed switch when conducting but turns off when current drops below the holding level. Key applications include use as a relaxation oscillator and triggering SCR devices.

1. SHOCKLEY DIODE
Prepared by
Barira Nashal

2. Contents
Introduction
Construction
Working or characteristics
Application

3. Introduction
The term Shockley diode or PNPN diode is named from the
inventor “William Shockley”.
It is a four layer semiconductor device and it was the first
semiconductor devices.
It is similar to a thyristor with detached gate.
This type of diode is not available commercially and not
particularly useful. But, this diode is more useful in making other
kinds of thyristors such as DIAC,TRIAC and SCR.

4. Internal Structure And Symbol

5. EquivalentCircuitDiagram

6. Construction
The construction of this diode is done by connecting the four
layers to form PNPN junction.The basic circuit of this diode using
two transistors. In the circuit, the collector terminal of the
T1 transistor is connected to the base terminal of theT2
transistor.
The J1 junction is designed at the EB junction ofT1 transistor,
J2 is at common connected BC junction betweenT1 &T2
transistors,
J3 is at BE junction ofT2 transistor.
So, as the BE junctions, J1& J3 must be forward biased & as a CB
junction, J2 must be reverse biased for linear operation.

7. Working
The shockley diode functions like a normal thyristor without any
trigger inputs . When the diode is in the forward, the current
flows through the diode, whereas in reverse bias, there is no flow
of current.
The Shockley diode comprises of three junctions namely J1, J2
and J3. Whenever the voltage is applied to the diode then the
anode terminal is made positive with respect to the cathode, J1
and J3 junctions are forward biased where J2 is reverse biased.

8. Forward Biasing
When the voltage is applied to the shockley diode in such a
way that anode is made positive with respect to cathode,
junctions J1 and J3 are forward biased and J2 is reverse biased.
Until the voltage across the diode is less than the break over
voltage, as an open switch shockley diode exhibits a very high
resistance and allows no current to flow through it.
Once the break over voltage is reached (as the forward
voltage is increased), it exhibits a very low resistance due to
the breakdown of junction J2.
Therefore, it acts like a short circuit and allows the current to
flow until the current reaches to the holding current level of
the diode.
ON-state current flows only when the voltage is more than
the break over voltageVBO.

9. Reverse Biasing
When the anode is made negative with respect to
the cathode, junctions J1 and J3 are reverse biased
and junction J2 is forward biased.
If the reverse bias voltage is increased (beyond
the breakdown voltage of the shockley diode), J1
and J3 are reverse biased, then the reverse current
will flow through the diode.
This reverse current produces the heat, further
this could ruin the entire diode.
Therefore, shockley diode should never be
operated in reverse biased condition with a
voltage equal to the reverse breakdown voltage.

10. To Turn Off Diode ..
Once the shockley diode is ON it acts like a closed switch offer a
very low resistance to the current flow.To turn OFF the diode,
the applied voltage must be reduced to a value such that current
flowing through the diode is less than the holding current IH of
the diode. In this state, junction J2 comes from reverse
breakdown state and restores its high resistance value.

11. Characteristics curve

12. Applications
1. Shockley Diode used as Relaxation
Oscillator:
When the battery voltage is applied to the circuit, the
capacitor charges through a resistance R.
When the applied voltage or voltage across the capacitor is
more than the break over voltage of shockley diode, it
becomes turned ON and acts as a Switch.
This causes rapidly to discharge the capacitor through the
diode.
When the current through the diode is less than the holding
current of the diode, the diode becomes turned OFF and
capacitor charges again.
The voltage across the capacitor isVBO where the voltage at
the reference is more than zero volts because the capacitor
will not discharge completely.

13. 2. Shockley Diode used asTrigger Switch:
Most common applications of shockley diode are
switching circuits , to turn ON the SCR. SCR is triggered
by the shockley diode.The Resistive and capacitor RC
network is fed with a DC supply which drives the
shockley diode.
When theVDC is applied, shockley is forward biased and
also capacitor starts charging through the resistance.
When the charging voltage of the capacitor reaches to
the break over voltage of the diode, diode starts
conducting and the capacitor starts discharging through
the diode.This conduction of shockley diode drives the
SCR into turn ON state, then the buzzer gives an alarm.
Once the SCR is turned ON it will remain in the latching
or ON state until the power is removed.The triggering
times of SCR is controlled by selecting proper values of
capacitor and resistors.

14. Thank You !!!