Power Semiconductor Devices

UJT as Over Voltage Detector Circuit Diagram: UJT as Over Voltage Detector Circuit Diagram – A simple dc overvoltage detector circuit is given in Fig. 26.96. It operates on the fact that the device remains switched off as long as the input voltage remain less than the peak point voltage VP of the UJT and […]

UJT Relaxation Oscillator – Circuit Diagram and its Workings: UJT Relaxation Oscillator – The relaxation oscillator shown in Fig. 26.94 (a) consists of UJT and a capacitor C which is charged through resistor RE when interbase voltage VBB is switched on. During the charging pe­riod, the voltage across the capacitor increases exponentially until it attains

UJT Triggering of SCR Working Principle: UJT Triggering of SCR Working Principle – One common application of the unijunction transistor is the triggering of the other devices such as the SCR, triac etc. The basic elements of such a triggering circuit are shown in Fig. 26.91. The resistor RE is chosen so that the load

Power BJT – Construction, Operation and its Characteristics: Power transistors are large-area devices. Because of differences in geometry and doping concentrations, their properties tend to vary from those of the small-signal devices. The structure of a vertical NPN power transistor is shown in Fig. 26.74. In the vertical con­figuration for power BJT, the collector terminal

Light Activated SCR (LASCR) – Symbol, Construction and Operation: Light activated SCR is just an ordinary SCR except that it can also be light triggered. Most LASCRs also have a gate terminal for be­ing triggered by an electrical pulse just as a conventional SCR. Construction: The basic construction of an Light Activated SCR (LASCR) is

Silicon Controlled Switch (SCS) – Symbol, Operation, Advantages and Application: Silicon controlled switch (SCS), like the SCR, is a unilateral, four layer, three junction P-N-P-N silicon device with four electrodes namely cathode C, cathode gate G1, anode gate G2 and the anode A, as shown in Fig. 26.59. Infact, the Silicon Controlled Switch is a

Gate Controlled Switch (GCS) Circuit – Operation and Advantages: As mentioned earlier, low-current drop out is the normal way in which the SCR is turned off. Gate controlled switch is designed for easy opening with a reverse-biased trigger. A GCS is closed by a positive trigger and opened by a negative trigger (or by low-current drop

Shockley Diode Equation, Symbol, Operation and Applications: The four layer diode, also called the Shockley diode after its in­ventor Willian Shockley, is essentially a low-current SCR without a gate. It is classified as a diode because it has only two exter­nal terminals viz. anode and cathode. Because of its four doped regions, it is often

What is DIAC? – Symbol, Construction, Operation and Applications A diac is an important member of the thyristor family and is usually employed for triggering triacs. A diac is a two electrode bidirectional avalanche diode which can be switched from off-state to the on-state for either polarity of the applied voltage. This is just like

SCR as Full Wave Rectifier Circuit Diagram: For Two SCR as Full Wave Rectifier are connected across the centre taped secondary, as shown in Fig. 26.32 (a). The gates of both SCRs are supplied from two gate control supply circuits. One SCR conducts during the + ve half cycle and the other during the -ve