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الکترونیک صنعتی دانشگاه تهران – بهزاد آسائی 1385 ترانزیستور Bipolar Junction Transistors (BJTs) 2 صنعتی الکترونیک BY: B. Asaei ترانزیستور Generic BJT Application Clamped Inductive Load 3 صنعتی الکترونیک BY: B. Asaei ترانزیستور Bipolar Junction Transistors (BJTs) C I I C B B D M D1 C D M+ D+ M B 4 صنعتی الکترونیک BY: B. Asaei MOSFET I-V Characteristics and Circuit Symbols i D [v - V GS = v ] GS(th) DS ohmic V GS5 active V GS4 V GS3 V GS2 VGS1 V 5 < GS V v GS(th) BV DS DSS صنعتی الکترونیک BY: B. Asaei MOSFET Switching Models for Buck Converter V D d Io D r DS(on) F R G C gd + V G GG C S • Buck converter using power MOSFET. • MOSFET equivalent circuit valid for on-state (triode) region operation. D C gd I = f(V ) GS D G C gs S 6 gs • MOSFET equivalent circuit valid for offstate (cutoff) and active region operation. صنعتی الکترونیک BY: B. Asaei Turn-on Equivalent Circuits for MOSFET Buck Converter • Equi val ent ci r cui t dur i ng t d(on) . D V in • I o F C R + V i GG Equi val ent ci r cui t dur i ng t r i . D G C • Equi val ent ci r cui t dur i ng t f v1 . C R G + V gs V in i GG G C V • Equi val ent ci r cui t dur i ng t f v2 . R G C gd1 + V + V 7 GG i DC C gd1 GG i G gs in I o R I o F DC C gd1 G V in I o DS(on) G C gs G صنعتی الکترونیک r BY: B. Asaei C gd2 MOSFET-based Buck Converter Turn-on Waveforms • Free-wheeling diode assumed to be ideal. (no reverse recovery current). 8 صنعتی الکترونیک BY: B. Asaei Paralleling of MOSFETs D • MOSFETs can be easily paralleled because of posit iv e t emperat ure coefficient of r DS( on) . Rd Q 1 G S • Posit iv e t emperat ure coefficient leads t o t hermal st abilizat ion effect . • If r DS( on) 1 > r DS( on) 2 t hen more current and t hus higher power dissipat ion in Q2 . • Temperat ure of Q2 t hus increases more t han t emperat ure of Q1 and r DS( on) v alues become equalized. 9 صنعتی الکترونیک BY: B. Asaei ارزیابی 10 As shown in Figure 1.1, a variety of circuitries in power electronics can be produced today with MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors), which were introduced into the market one by one in the mid 80’s. Compared to other switchable power semiconductors, such as conventional GTO-thyristors, these types of transistors have a number of application advantages, such as active turn-off even in case of short-circuit, operation without snubbers, simple control unit, short switching times and, therefore, relatively low switching losses. The production of MOSFETs and IGBTs is comparatively simple and favourable and can easily be managed by today’s technologies in microelectronics. It was mainly due to the rapid development of IGBTs and power MOSFETs that power electronics continued open up new markets, and that their fields of application increased tremendously at the same time. Bipolar high-voltage power transistors that were still very common a few years ago, have been almost completely replaced by IGBTs. صنعتی الکترونیک BY: B. Asaei