1 / 65

UNIT I

UNIT I. Power Semiconductor Devices. Introduction. What are Power Semiconductor Devices (PSD)? They are devices used as switches or rectifiers in power electronic circuits What is the difference of PSD and low-power semiconductor device? Large voltage in the off state

polkr
Download Presentation

UNIT I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. UNIT I Power Semiconductor Devices

  2. Introduction • What are Power Semiconductor Devices (PSD)? They are devices used as switches or rectifiers in power electronic circuits • What is the difference of PSD and low-power semiconductor device? • Large voltage in the off state • High current capability in the on state EE2301-POWER ELECTRONICS

  3. Classification Fig. 1. The power semiconductor devices family EE2301-POWER ELECTRONICS

  4. Important Parameters • Breakdown voltage. • On-resistance. Trade-off between breakdown voltage and on-resistance. • Rise and fall times for switching between on and off states. • Safe-operating area. EE2301-POWER ELECTRONICS

  5. Power MOSFET: Structure Power MOSFET has much higher current handling capability in ampere range and drain to source blocking voltage(50-100V) than other MOSFETs. Fig.2.Repetitive pattern of the cells structure in power MOSFET EE2301-POWER ELECTRONICS

  6. Power MOSFET: R-V Characteristics An important parameter of a power MOSFET is on resistance: , where Fig. 3. Typical RDS versus ID characteristics of a MOSFET. EE2301-POWER ELECTRONICS

  7. Thyristor: Structure • Thyristor is a general class of a four-layer pnpn semiconducting device. Fig.4 (a) The basic four-layer pnpn structure. (b) Two two-transistor equivalent circuit. EE2301-POWER ELECTRONICS

  8. Thyristor: I-V Characteristics Three States: • Reverse Blocking • Forward Blocking • Forward Conducting Fig.5 The current-voltage characteristics of the pnpn device. EE2301-POWER ELECTRONICS

  9. Applications Power semiconductor devices have widespread applications: • Automotive Alternator, Regulator, Ignition, stereo tape • Entertainment Power supplies, stereo, radio and television • Appliance Drill motors, Blenders, Mixers, Air conditioners and Heaters EE2301-POWER ELECTRONICS

  10. Thyristors • Most important type of power semiconductor device. • Have the highest power handling capability.they have a rating of 1200V / 1500A with switching frequencies ranging from 1KHz to 20KHz. EE2301-POWER ELECTRONICS

  11. Is inherently a slow switching device compared to BJT or MOSFET. • Used as a latching switch that can be turned on by the control terminal but cannot be turned off by the gate. EE2301-POWER ELECTRONICS

  12. Different types of Thyristors • Silicon Controlled Rectifier (SCR). • TRIAC. • DIAC. • Gate Turn-Off Thyristor (GTO). EE2301-POWER ELECTRONICS

  13. SCR Symbol of Silicon Controlled Rectifier EE2301-POWER ELECTRONICS

  14. Structure EE2301-POWER ELECTRONICS

  15. Device Operation Simplified model of a thyristor EE2301-POWER ELECTRONICS

  16. V-I Characteristics EE2301-POWER ELECTRONICS

  17. Effects of gate current EE2301-POWER ELECTRONICS

  18. Two Transistor Model of SCR  EE2301-POWER ELECTRONICS

  19. EE2301-POWER ELECTRONICS

  20. EE2301-POWER ELECTRONICS

  21. EE2301-POWER ELECTRONICS

  22. EE2301-POWER ELECTRONICS

  23. EE2301-POWER ELECTRONICS

  24. Turn-on Characteristics EE2301-POWER ELECTRONICS

  25. Turn-off Characteristic EE2301-POWER ELECTRONICS

  26. Methods of Thyristor Turn-on • Thermal Turn-on. • Light. • High Voltage. • Gate Current. • dv/dt. EE2301-POWER ELECTRONICS

  27. Thyristor Types • Phase-control Thyristors (SCR’s). • Fast-switching Thyristors (SCR’s). • Gate-turn-off Thyristors (GTOs). • Bidirectional triode Thyristors (TRIACs). • Reverse-conducting Thyristors (RCTs). EE2301-POWER ELECTRONICS

  28. Static induction Thyristors (SITHs). • Light-activated silicon-controlled rectifiers (LASCRs). • FET controlled Thyristors (FET-CTHs). • MOS controlled Thyristors (MCTs). EE2301-POWER ELECTRONICS

  29. Phase Control Thyristor • These are converter thyristors. • The turn-off time tq is in the order of 50 to 100sec. • Used for low switching frequency. • Commutation is natural commutation • On state voltage drop is 1.15V for a 600V device. EE2301-POWER ELECTRONICS

  30. They use amplifying gate thyristor. EE2301-POWER ELECTRONICS

  31. Fast Switching Thyristors • Also called inverter thyristors. • Used for high speed switching applications. • Turn-off time tq in the range of 5 to 50sec. • On-state voltage drop of typically 1.7V for 2200A, 1800V thyristor. • High dv/dt and high di/dt rating. EE2301-POWER ELECTRONICS

  32. Bidirectional Triode Thyristors (TRIAC) EE2301-POWER ELECTRONICS

  33. Mode-I Operation MT2 Positive, Gate Positive EE2301-POWER ELECTRONICS

  34. Mode-II Operation MT2 Positive, Gate Negative EE2301-POWER ELECTRONICS

  35. Mode-III Operation MT2 Negative, Gate Positive EE2301-POWER ELECTRONICS

  36. Mode-IV Operation MT2 Negative, Gate Negative EE2301-POWER ELECTRONICS

  37. Triac Characteristics EE2301-POWER ELECTRONICS

  38. BJT structure heavily doped ~ 10^15 provides the carriers lightlydoped~ 10^8 lightlydoped ~ 10^6 note: this is a current of electrons (npn case) and so the conventional current flows from collector to emitter. EE2301-POWER ELECTRONICS

  39. BJT characteristics EE2301-POWER ELECTRONICS

  40. BJT characteristics EE2301-POWER ELECTRONICS

  41. BJT modes of operation EE2301-POWER ELECTRONICS

  42. BJT modes of operation Cutoff: In cutoff, both junctions reverse biased. There is very little current flow, which corresponds to a logical "off", or an open switch. Forward-active (or simply, active): The emitter-base junction is forward biased and the base-collector junction is reverse biased. Most bipolar transistors are designed to afford the greatest common-emitter current gain, βf in forward-active mode. If this is the case, the collector-emitter current is approximately proportional to the base current, but many times larger, for small base current variations. Reverse-active (or inverse-active or inverted): By reversing the biasing conditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Since most BJTs are designed to maximise current gain in forward-active mode, the βf in inverted mode is several times smaller. This transistor mode is seldom used. The reverse bias breakdown voltage to the base may be an order of magnitude lower in this region. Saturation: With both junctions forward-biased, a BJT is in saturation mode and facilitates current conduction from the emitter to the collector. This mode corresponds to a logical "on", or a closed switch. EE2301-POWER ELECTRONICS

  43. IE IC - VCE + E C - + VBE VCB IB + - B BJT structure (active) current of electrons for npn transistor – conventional current flows from collector to emitter. EE2301-POWER ELECTRONICS

  44. L = channel length W • W = channel width n n L oxide insulator MOSFET • NMOS:N-channel Metal • Oxide Semiconductor GATE “Metal” (heavily doped poly-Si) DRAIN p-type silicon SOURCE • A GATE electrode is placed above (electrically insulated from) the silicon surface, and is used to control the resistance between the SOURCE and DRAIN regions EE2301-POWER ELECTRONICS

  45. n n gate oxide insulator N-channel MOSFET Gate IG Drain Source IS ID p • Without a gate-to-source voltage applied, no current can flow between the source and drain regions. • Above a certain gate-to-source voltage (threshold voltageVT), a conducting layer of mobile electrons is formed at the Si surface beneath the oxide. These electrons can carry current between the source and drain. EE2301-POWER ELECTRONICS

  46. n+ poly-Si p+ poly-Si p-type Si n-type Si N-channel vs. P-channel MOSFETs NMOS PMOS • For current to flow, VGS > VT • Enhancement mode: VT > 0 • Depletion mode: VT < 0 • Transistor is ON when VG=0V n+ n+ p+ p+ • For current to flow, VGS < VT • Enhancement mode: VT < 0 • Depletion mode: VT > 0 • Transistor is ON when VG=0V (“n+” denotes very heavily doped n-type material; “p+” denotes very heavily doped p-type material) EE2301-POWER ELECTRONICS

  47. p+ poly-Si n+ poly-Si Body Body n-type Si p-type Si MOSFET Circuit Symbols G G NMOS n+ n+ S S G G PMOS p+ p+ S S EE2301-POWER ELECTRONICS

  48. MOSFET Terminals • The voltage applied to the GATE terminal determines whether current can flow between the SOURCE & DRAIN terminals. • For an n-channel MOSFET, the SOURCE is biased at a lower potential (often 0 V) than the DRAIN (Electrons flow from SOURCE to DRAIN when VG > VT) • For a p-channel MOSFET, the SOURCE is biased at a higher potential (often the supply voltage VDD) than the DRAIN (Holes flow from SOURCE to DRAIN when VG < VT ) • The BODY terminal is usually connected to a fixed potential. • For an n-channel MOSFET, the BODY is connected to 0 V • For a p-channel MOSFET, the BODY is connected to VDD EE2301-POWER ELECTRONICS

  49. + +   NMOSFET IGvs.VGS Characteristic Consider the current IG (flowing into G) versus VGS : IG G S D VDS oxide semiconductor VGS IG The gate is insulated from the semiconductor, so there is no significant steady gate current. always zero! VGS EE2301-POWER ELECTRONICS

  50. The MOSFET as a Controlled Resistor • The MOSFET behaves as a resistor when VDS is low: • Drain current ID increases linearly with VDS • Resistance RDS between SOURCE & DRAIN depends on VGS • RDS is lowered as VGS increases above VT NMOSFET Example: oxide thickness tox ID VGS = 2 V VGS = 1 V > VT VDS Inversion charge density Qi(x) = -Cox[VGS-VT-V(x)] where Coxeox / tox IDS = 0 if VGS< VT EE2301-POWER ELECTRONICS

More Related