21-03-2014, 03:26 PM
Special Semiconductor Devices
[attachment=60386]
OBJECTIVE
In this chapter various semiconductor devices are dealt with in detail. Power electronic Devices play a major role in modern electronic design. High-power semiconductor devices have better switching speed, they are smaller in size and cost of production is also low.
Subsequently, the SCR,TRIAC, DIAC, UJT and IGBT are discussed in a similar manner with respect to their real life application.
INTRODUCTION
The SCR is the most important special semiconductor device. This device is popular for its Forward-Conducting and Reverse-blocking characteristics.
SCR can be used in high-power devices. For example, in the central processing unit of the computer, the SCR is used in switch mode power supply (SMPS).
The DIAC, a combination of two Shockley Diodes, and the TRIAC, a combination of two SCRs connected
anti-parallelly are important power-control devices. The UJT is also used as an efficient switching device.
SCR in Forward Bias:
There are two different states in which we can examine the SCR in the forward-biased condition:
(i) The high- impedance or forward-blocking state
(ii) The low-impedance or forward-conducting state
At a critical peak forward voltage Vp, the SCR switches from the blocking state to the conducting state, as shown in Fig. 8-2.
A positive voltage places junction j1 and j3 under forward-bias, and the centre junction j2 under reverse-bias.
The for ward voltage in the blocking state appears across the reverse-biased junc tion j2 as the applied voltage V is increased. The voltage from the anode A to cathode C, as shown in Fig. 8-1, is very small after switching to the forward-conducting state, and all three junctions are forward-biased. The junction j2 switches from reverse-bias to forward-bias..
Simple Applications:
The SCR is the most important member of the thyristor family. The SCR is a capable power device as it can handle thousands of amperes and volts.
Generally the SCR is used in many applications such as in high power electronics, switches, power-control and conversion mode.
It is also used as surge protector.
Static Switch: The SCR is used as a switch for power-switching in various control circuits.
Power Control: Since the SCR can be turned on externally, it can be used to regulate the amount of power delivered to a load.
Surge Protection: In an SCR circuit, when the voltage rises beyond the threshold value, the SCR is turned on to dissipate the charge or voltage quickly.
Power Conversion: The SCR is also used for high-power conversion and regulation. This includes conversion of power source from ac to ac, ac to dc and dc to ac.
[attachment=60386]
OBJECTIVE
In this chapter various semiconductor devices are dealt with in detail. Power electronic Devices play a major role in modern electronic design. High-power semiconductor devices have better switching speed, they are smaller in size and cost of production is also low.
Subsequently, the SCR,TRIAC, DIAC, UJT and IGBT are discussed in a similar manner with respect to their real life application.
INTRODUCTION
The SCR is the most important special semiconductor device. This device is popular for its Forward-Conducting and Reverse-blocking characteristics.
SCR can be used in high-power devices. For example, in the central processing unit of the computer, the SCR is used in switch mode power supply (SMPS).
The DIAC, a combination of two Shockley Diodes, and the TRIAC, a combination of two SCRs connected
anti-parallelly are important power-control devices. The UJT is also used as an efficient switching device.
SCR in Forward Bias:
There are two different states in which we can examine the SCR in the forward-biased condition:
(i) The high- impedance or forward-blocking state
(ii) The low-impedance or forward-conducting state
At a critical peak forward voltage Vp, the SCR switches from the blocking state to the conducting state, as shown in Fig. 8-2.
A positive voltage places junction j1 and j3 under forward-bias, and the centre junction j2 under reverse-bias.
The for ward voltage in the blocking state appears across the reverse-biased junc tion j2 as the applied voltage V is increased. The voltage from the anode A to cathode C, as shown in Fig. 8-1, is very small after switching to the forward-conducting state, and all three junctions are forward-biased. The junction j2 switches from reverse-bias to forward-bias..
Simple Applications:
The SCR is the most important member of the thyristor family. The SCR is a capable power device as it can handle thousands of amperes and volts.
Generally the SCR is used in many applications such as in high power electronics, switches, power-control and conversion mode.
It is also used as surge protector.
Static Switch: The SCR is used as a switch for power-switching in various control circuits.
Power Control: Since the SCR can be turned on externally, it can be used to regulate the amount of power delivered to a load.
Surge Protection: In an SCR circuit, when the voltage rises beyond the threshold value, the SCR is turned on to dissipate the charge or voltage quickly.
Power Conversion: The SCR is also used for high-power conversion and regulation. This includes conversion of power source from ac to ac, ac to dc and dc to ac.