शक्ति अर्धचालक युक्तियाँ

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प्रमुख शक्ति युक्तियों का धारा/वोल्टता/आवृति डोमेन

शक्ति एलेक्ट्रानिकी के क्षेत्र में शक्ति-परिपथों में प्रयुक्त होने वाली अर्धचालक युक्तियों को शक्ति अर्धचालक युक्ति (power semiconductor device) कहते हैं। ये दिष्टकारी के रूप में या स्विच के रूप में प्रयुक्त होती हैं। ये युक्तियाँ प्रायः पूर्णतः चालू (आन) या पूर्णतः बन्द (आफ) अवस्था में रहती हैं और इसी प्रकार के उपयोग के लिए डिजाइन भी की जाती हैं। ये प्रायः 'रैखिक अवस्था' (लिनियर मोड) में काम में नहीं ली जातीं।

ठोस अवस्था शक्ति-युक्तियाँ[संपादित करें]

सिलिखॉन आधारित युक्तियाँ व्यख्या उदाहरण
डायड एकध्रुवी, अनियंत्रित स्विच करने वाली युक्ति। इसका उपयोग ऋजुकरण (rectification) में होता है। यह व्युत्क्रम वोल्टता को धारा बहाने से रोकती है। इसको प्रायः एक वोल्टता स्रोत (प्रायः 0.7 VDC) के श्रेणीक्रम में एक स्विच लगाकर मॉडल किया जाता है। इस मॉडल में जंक्सन प्रतिरोध को भी शामिल करके इसे और उन्नत बनाया जा सकता है। [[File:Diode pinout en fr.svg|thumb|center|200px|डायोड का प्रतीक और कुछ छोटे डायोड। पतली पट्टी डायोड का कैथोड है।
एससीआर (SCR) यह अर्ध-नियंत्रित युक्ति है जो गेट पल्स देने पर चालू हो जाती है यदि उस समय इसका एनोड कैथोड की अपेक्षा धनात्मक विभव पर हो। किन्तु एससीआर को गेट की सहायता से आफ नहीं किया जा सकता। चालू होने के बाद यह तभी आफ होगा जब इसकी धारा एक निश्चित मात्रा से कम (लगभग शून्य) हो जाय। .[1] [[File:Thyristor circuit symbol.svg|thumb|x120px|540px|center|Electronic symbol|Circuit symbol for a silicon-controlled rectifier.]]
थाइरिस्टर यह युक्तियों के एक परिवार का नाम है जिसमें एससीआर, GTOs और MCT शामिल है। For most of the devices, a gate pulse turns the device on. The device turns off when the reverse voltage at the anode is more negative than the cathode. When off, it is considered a reverse voltage blocking device.[1]
Circuit symbol for a thyristor.
जीटीओ (GTO) The gate turn-off thyristor, unlike an SCR, can be turned on and off with a gate pulse. One issue with the device is that turn off gate voltages are usually larger and require more current than turn on levels. This turn off voltage is a negative voltage from gate to source, usually it only needs to be present for a short time, but the magnitude s on the order of 1/3 of the anode current. A snubber circuit is required in order to provide a usable switching curve for this device. Without the snubber circuit, the GTO cannot be used for turning inductive loads off. These devices, because of developments in IGCT technology are not very popular in the power electronics realm. They are considered controlled, uni-polar and bi-polar voltage blocking.[2]
ट्रायक (TRIAC) The triac is a device that is essentially an integrated pair of phase-controlled thyristors connected in inverse-parallel on the same chip.[3] Like an SCR, when a voltage pulse is present on the gate terminal, the device turns on. The main difference between an SCR and a Triac is that both the positive and negative cycle can be turned on independently of each other, using a positive or negative gate pulse. Similar to an SCR, once the device is turned on, the device cannot be turned off. This device is considered bi-polar and reverse voltage blocking.
Triac schematic symbol.
बीजेटी (BJT) The BJT cannot be used at high power; they are slower and have more resistive losses when compared to MOSFET type devices. In order to carry high current, BJTs must have relatively large base currents, thus these devices have high power losses when compared to MOSFET devices. BJTs along with MOSFETs, are also considered unipolar and do not block reverse voltage very well, unless installed in pairs with protection diodes. Generally, BJTs are not utilized in power electronics switching circuits because of the I2R losses associated with on resistance and base current requirements.[1] BJTs have lower current gains in high power packages, thus requiring them to be setup in Darlington configurations in order to handle the currents required by power electronic circuits. Because of these multiple transistor configurations, switching times are in the hundreds of nanoseconds to microseconds. Devices have voltage ratings which max out around 1500 V and fairly high current ratings. They can also be paralleled in order to increase power handling, but must be limited to around 5 devices for current sharing.[2]
The symbol of a PNP Bipolar junction transistor. The symbol "points in proudly."
The symbol of an NPN BJT. The symbol is "not pointing in."
पॉवर मॉसफेट The main benefit of the power MOSFET is that the base current for BJT is large compared to almost zero for MOSFET gate current. Since the MOSFET is a depletion channel device, voltage, not current is necessary to create a conduction path from drain to source. The gate does not contribute to either drain or source current. Turn on gate current is essentially zero with the only power dissipated at the gate coming during switching. Losses in MOSFETs are largely attributed to on-resistance. The calculations show a direct correlation to drain source on-resistance and the device blocking voltage rating, BVdss.

Switching times range from tens of nanoseconds to a few hundred microseconds, depending on the device. MOSFET drain source resistances increase as more current flows through the device. As frequencies increase the losses increase as well, making BJTs more attractive. Power MOSFETs can be paralleled in order to increase switching current and therefore overall switching power. Nominal voltages for MOSFET switching devices range from a few volts to a little over 1000 V, with currents up to about 100 A or so. Newer devices may have higher operational characteristics. MOSFET devices are not bi-directional, nor are they reverse voltage blocking.[2]

Cross section of a VDMOS, showing an elementary cell. Note that a cell is very small (some micrometres to some tens of micrometres wide), and that a power MOSFET is composed of several thousand of them.
आईजीबीटी (IGBT) These devices have the best characteristics of MOSFETs and BJTs. Like MOSFET devices, the insulated gate bipolar transistor has a high gate impedance, thus low gate current requirements. Like BJTs, this device has low on state voltage drop, thus low power loss across the switch in operating mode. Similar to the GTO, the IGBT can be used to block both positive and negative voltages. Operating currents are fairly high, in excess of 1500 A and switching voltage up to 3000 V.[2] The IGBT has reduced input capacitance compared to MOSFET devices which improves the Miller feedback effect during high dv/dt turn on and turn off.[3]
Electronic symbol for depletion-mode IGBT.
MOS Controlled Thyristor (MCT) The MOS controlled thyristor is thyristor like and can be triggered on or off by a pulse to the MOSFET gate.[3] Since the input is MOS technology, there is very little current flow, allowing for very low power control signals. The device is constructed with two MOSFET inputs and a pair of BJT output stages. Input MOSFETs are configured to allow turn on control during positive and negative half cycles. The output BJTs are configured to allow for bidirectional control and low voltage reverse blocking. Some benefits to the MCT are fast switching frequencies, fairly high voltage and medium current ratings (around 100 A or so).
Circuit symbol for a MOS Controlled Thyristor.
आईजीसीटी (IGCT) Similar to a GTO, but without the high current requirements to turn on or off the load. The IGCT can be used for quick switching with little gate current. The devices high input impedance largely because of the MOSFET gate drivers. They have low resistance outputs that don't waste power and very fast transient times that rival that of BJTs. ABB has published data sheets for these devices and provided descriptions of the inner workings. The device consists of a gate, with an optically isolated input, low on resistance BJT output transistors which lead to a low voltage drop and low power loss across the device at fairly high switching voltage and current levels.

An example of this new device from ABB shows how this device improves on GTO technology for switching high voltage and high current in power electronics applications. According to ABB, the IGCT devices are capable of switching in excess of 5000 VAC and 5000 A at very high frequencies, something not possible to do efficiently with GTO devices.[4]

Circuit symbol for an integrated gate-commutated thyristor.

सन्दर्भ[संपादित करें]

  1. Hart, D. (2010). Power Electronics. McGraw-Hill Education. pp. Chapter 1. आई॰ऍस॰बी॰ऍन॰ 978-0-07-128930-6. 
  2. Mohan, N. (2003). Power Electronics Converters Applications and Design. Michigan: John Wiley and Sons. pp. Chapter 1. आई॰ऍस॰बी॰ऍन॰ 978-0-471-22693-2. 
  3. Bose, B (April 1992). "Evaluation of Modern Power Semiconductor Devices and Future Trends of Converters". IEEE Transactions on Industry Applications 28 (2). 
  4. "semiconductor GTO". GTO. ABB. http://www.abb.com/product/us/9AAC30301124.aspx?country=US. अभिगमन तिथि: 21 मार्च 2012. 

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