Silicon Controlled Rectifier Overview
171 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What role does a Silicon Controlled Rectifier (SCR) primarily serve?

  • It converts AC current into RF signals.
  • It generates alternating current from direct current.
  • It allows DC current to flow in both directions.
  • It controls high power and converts AC to DC. (correct)

    • How many terminals and layers does a Silicon Controlled Rectifier have?

  • 3 terminals and 3 layers
  • 4 terminals and 4 layers
  • 2 terminals and 2 layers
  • 3 terminals and 4 layers (correct)

    • Which of the following terms is commonly used interchangeably with Silicon Controlled Rectifier?

  • Oscillator
  • P-N Junction Diode
  • Transistor
  • 4-Layer Device (correct)

    • What is the main advantage of Silicon Controlled Rectifiers over normal diodes?

    <p>They operate at higher voltages.</p> Signup and view all the answers

    What type of current do Silicon Controlled Rectifiers predominantly control?

    <p>Alternating Current</p> Signup and view all the answers

    What were the primary contributions made by Tanenbaum, Goldey, Moll, and Holonyak?

    <p>Development of p-n-p-n switching</p> Signup and view all the answers

    In what year was the Silicon Controlled Rectifier commercialized?

    <p>1957</p> Signup and view all the answers

    Which of the following applications is NOT typically associated with Silicon Controlled Rectifiers?

    <p>Transforming AC to RF signals</p> Signup and view all the answers

    What is the function of the gate terminal in a Silicon Controlled Rectifier?

    <p>It controls the flow of current between the anode and cathode.</p> Signup and view all the answers

    What happens to the depletion region at junction J2 in Forward Blocking Mode?

    <p>It widens and blocks current flow.</p> Signup and view all the answers

    What happens in the forward blocking region of an SCR when a positive voltage is applied to the anode?

    <p>A small leakage current flows from anode to cathode.</p> Signup and view all the answers

    Which of the following describes the structure of a Silicon Controlled Rectifier?

    <p>A PNPN structure with four semiconductor layers.</p> Signup and view all the answers

    What is the condition that leads to the SCR entering its forward conduction region?

    <p>The forward bias voltage is increased beyond the breakdown voltage.</p> Signup and view all the answers

    In which mode does the SCR allow a small amount of leakage current to flow?

    <p>Forward Blocking Mode.</p> Signup and view all the answers

    What is the effect of applying a positive voltage to the gate terminal during Forward Blocking Mode?

    <p>It narrows the depletion region at junction J2.</p> Signup and view all the answers

    In the reverse blocking region of an SCR, what occurs when a negative voltage is applied to the anode?

    <p>A small leakage current flows due to drift in junction J2.</p> Signup and view all the answers

    What causes the SCR to transition into Forward Conducting Mode?

    <p>Applying voltage to the gate terminal.</p> Signup and view all the answers

    What is the critical voltage level called at which junction J2 gets broken when the gate is open?

    <p>Forward breakdown voltage.</p> Signup and view all the answers

    Which of the following best describes a TRIAC?

    <p>A bidirectional device that controls both DC and AC.</p> Signup and view all the answers

    What happens in Reverse Blocking Mode?

    <p>Junctions J1 and J3 are reverse biased.</p> Signup and view all the answers

    What type of semiconductor is formed when pentavalent impurities are added to silicon?

    <p>N-type semiconductor.</p> Signup and view all the answers

    What occurs when the gate and MT2 of a TRIAC are at positive potential with respect to MT1?

    <p>Current flows through P1-N1 and P2-N2.</p> Signup and view all the answers

    Which junctions are formed in the PNPN structure of an SCR?

    <p>Junctions J1, J2, J3 only.</p> Signup and view all the answers

    What role does the gate terminal play in the operation of a TRIAC?

    <p>It influences the turn-on conditions of the device.</p> Signup and view all the answers

    In the event of an avalanche breakdown in reverse bias, what is the likely outcome for the SCR?

    <p>The SCR is damaged due to rapid increase in current.</p> Signup and view all the answers

    What causes avalanche breakdown in an SCR?

    <p>High energy minority carriers at breakdown voltage.</p> Signup and view all the answers

    Which current is generated in reverse block region but is insufficient to turn on the SCR?

    <p>Reverse leakage current.</p> Signup and view all the answers

    How does forward biasing affect the junctions in the SCR?

    <p>It facilitates conduction by reducing the depletion width.</p> Signup and view all the answers

    What is the primary function of the SCR in power electronics?

    <p>To control the flow of electric current.</p> Signup and view all the answers

    Which material is primarily used to construct the SCR?

    <p>Silicon.</p> Signup and view all the answers

    Which mode of operation allows for current to flow after breakdown occurs?

    <p>Forward Conducting Mode.</p> Signup and view all the answers

    What happens to the voltage across an SCR as soon as it turns on after reaching breakdown?

    <p>It drops to a few volts.</p> Signup and view all the answers

    Which statement about the structure of a TRIAC is true?

    <p>It is composed of two SCRs in parallel along with a gate terminal.</p> Signup and view all the answers

    What is the main characteristic of Reverse Blocking Mode in an SCR?

    <p>Only gate terminal is forward biased.</p> Signup and view all the answers

    How does the SCR behave when the applied voltage is below the breakdown value?

    <p>It behaves as an insulator.</p> Signup and view all the answers

    In mode 1 of TRIAC characteristics, what are the conditions for its operation?

    <p>Both VMT21 and VG1 are positive.</p> Signup and view all the answers

    What defines the reverse avalanche region for an SCR?

    <p>Current increases rapidly with increasing reverse bias voltage.</p> Signup and view all the answers

    In which mode is VMT21 positive and VG1 negative?

    <p>Mode 2</p> Signup and view all the answers

    What is the purpose of the external resistance in a TRIAC circuit?

    <p>To limit excess current</p> Signup and view all the answers

    What defines the on-state current for a typical TRIAC?

    <p>25 A</p> Signup and view all the answers

    Which component is primarily responsible for triggering other devices like TRIAC?

    <p>DIAC</p> Signup and view all the answers

    What is a key disadvantage of using a TRIAC compared to SCR?

    <p>Lower availability of ratings</p> Signup and view all the answers

    What happens when the applied voltage at MT1 of a DIAC does not exceed the break over voltage?

    <p>The DIAC remains in off-state</p> Signup and view all the answers

    Which of the following is NOT a component of the DIAC?

    <p>Gate terminal</p> Signup and view all the answers

    Which characteristic of the DIAC allows it to conduct in both directions?

    <p>Symmetrical structure</p> Signup and view all the answers

    The V-I characteristics of a DIAC resemble which letter when plotted?

    <p>Z</p> Signup and view all the answers

    What type of control does a TRIAC provide in AC applications?

    <p>Both on and off control</p> Signup and view all the answers

    What is the average triggering current for a typical TRIAC?

    <p>5 mA</p> Signup and view all the answers

    What happens to the DIAC once the current falls below its holding current limit?

    <p>It switches to off-state</p> Signup and view all the answers

    During which part of the input cycle does the TRIAC switch D1 forward biased?

    <p>Positive half cycle</p> Signup and view all the answers

    Which layer structure is primarily used in constructing a DIAC?

    <p>3-layer structure</p> Signup and view all the answers

    What is the holding current for a typical TRIAC?

    <p>75 mA</p> Signup and view all the answers

    What causes the IGBT to switch ON?

    <p>Exceeding threshold voltage with positive gate voltage</p> Signup and view all the answers

    What distinguishes punch through IGBTs from non punch through IGBTs?

    <p>Asymmetric voltage blocking capabilities</p> Signup and view all the answers

    In which scenario does the IGBT remain in the cutoff mode?

    <p>When VGE is less than VGET</p> Signup and view all the answers

    What is a major disadvantage of IGBTs compared to MOSFETs?

    <p>Inability to block higher reverse voltage</p> Signup and view all the answers

    Which type of IGBT can handle reverse voltages?

    <p>Non punch through IGBT</p> Signup and view all the answers

    What happens to the collector current IC when the gate-emitter voltage VGE is increased above the threshold voltage VGET?

    <p>IC exponentially increases</p> Signup and view all the answers

    Which application is NOT typically associated with IGBTs?

    <p>Digital signal processing</p> Signup and view all the answers

    What characteristic sets IGBTs apart from BJTs?

    <p>Voltage control instead of current control</p> Signup and view all the answers

    What is the primary function of the N+ buffer layer in punch through IGBTs?

    <p>To create asymmetric breakdown voltage characteristics</p> Signup and view all the answers

    What is a primary advantage of using a DIAC in circuits?

    <p>It offers symmetrical switching characteristics.</p> Signup and view all the answers

    What is the effect of excess reverse voltage on IGBT operation?

    <p>Uncontrolled current flow occurs</p> Signup and view all the answers

    Which of the following best describes the 1st and 3rd quadrants in the operation of a device like a DIAC?

    <p>They differ only in the direction of voltage and current.</p> Signup and view all the answers

    What is the main function of a DIAC in relation to a TRIAC?

    <p>To trigger the TRIAC at equal voltage levels for both AC cycles.</p> Signup and view all the answers

    Which statement is true regarding the current through the cathode terminal in a SCR?

    <p>It is the sum of the gate current and anode current.</p> Signup and view all the answers

    What happens during the regeneration process of an SCR after it is triggered?

    <p>It reinforces the triggering effect through feedback.</p> Signup and view all the answers

    What is a disadvantage of using a DIAC?

    <p>It is not effective in high voltage applications.</p> Signup and view all the answers

    In the two transistor analogy of an SCR, what connects the collector of each transistor?

    <p>The base of the other transistor.</p> Signup and view all the answers

    What is the effect of asymmetrical triggering in a TRIAC?

    <p>It generates harmonics in the system.</p> Signup and view all the answers

    Which method can be used to turn on a Silicon Controlled Rectifier (SCR)?

    <p>Providing a short-duration pulse to the gate.</p> Signup and view all the answers

    What does the term 'holding current' refer to in the context of SCR operation?

    <p>The current below which the SCR turns off.</p> Signup and view all the answers

    What is one of the key requirements for a successful SCR turn-on?

    <p>The timing of the triggering signal must be appropriate.</p> Signup and view all the answers

    What occurs if the anode current of an SCR falls below the holding current?

    <p>The SCR turns off automatically.</p> Signup and view all the answers

    In terms of their switching characteristics, how do DIACs operate?

    <p>They provide symmetrical switching characteristics.</p> Signup and view all the answers

    What is the implication of a low on-state voltage drop in a DIAC?

    <p>It allows better power efficiency during operation.</p> Signup and view all the answers

    What is a characteristic of the forward blocking mode in an SCR?

    <p>Both J1 and J3 are forward biased.</p> Signup and view all the answers

    Which triggering method uses light to activate the SCR?

    <p>Light Triggering</p> Signup and view all the answers

    Why is forward voltage triggering not recommended in practice?

    <p>It may destroy the device due to overheating.</p> Signup and view all the answers

    What occurs in the SCR during thermal triggering?

    <p>Leakage current increases with temperature.</p> Signup and view all the answers

    How does dV/dt triggering work in SCRs?

    <p>By producing a gate current when voltage rises rapidly.</p> Signup and view all the answers

    What is the role of the gate terminal in gate triggering?

    <p>It injects electrons into the P-layer.</p> Signup and view all the answers

    Which method of triggering is described as the most reliable for SCR?

    <p>Gate Triggering</p> Signup and view all the answers

    What happens if the gate current is applied during reverse bias?

    <p>The SCR may be damaged.</p> Signup and view all the answers

    Which method is NOT recommended for turning ON an SCR?

    <p>Forward Voltage Triggering</p> Signup and view all the answers

    What condition must be met for gate triggering to start conducting in SCR?

    <p>Gate voltage must be applied correctly.</p> Signup and view all the answers

    Which statement is true about the temperature effect on SCR operation?

    <p>Increased temperature can lead to thermal runaway.</p> Signup and view all the answers

    What is the primary risk of using dV/dt triggering for SCR operation?

    <p>It may lead to undesired triggering from voltage spikes.</p> Signup and view all the answers

    What happens to the SCR when the breakdown of junction J2 occurs during forward voltage triggering?

    <p>Conduction begins from anode to cathode.</p> Signup and view all the answers

    What is the main advantage of using pulse triggering compared to AC triggering for SCR?

    <p>Reduced gate losses</p> Signup and view all the answers

    What condition must be met for the gate current in a thyristor firing circuit?

    <p>It must be of sufficient amplitude and duration</p> Signup and view all the answers

    Which firing circuit allows for a firing angle range between 0° to 90°?

    <p>Resistance firing circuit</p> Signup and view all the answers

    When is a thyristor turned ON during the AC supply cycle?

    <p>During the positive half cycle only</p> Signup and view all the answers

    What happens during the negative half cycle of the current supply to the thyristor?

    <p>It is reverse-biased and turns OFF</p> Signup and view all the answers

    What is the role of the diode in the resistance firing circuit?

    <p>To prevent reverse voltage exceeding peak reverse voltage</p> Signup and view all the answers

    What is a common feature of most firing circuits for thyristors?

    <p>Usage of low-power semiconductor devices</p> Signup and view all the answers

    What is a significant disadvantage of the resistance firing circuit?

    <p>Limited range of firing angles</p> Signup and view all the answers

    How does varying the resistance in an R-firing circuit affect the firing angle?

    <p>Increases the firing angle as resistance increases</p> Signup and view all the answers

    What determines when a thyristor loses its control from the gate?

    <p>Once the thyristor is turned ON</p> Signup and view all the answers

    Which of the following is NOT a type of commonly used firing circuit for thyristors?

    <p>Field-effect firing circuit</p> Signup and view all the answers

    Which of the following operating characteristics is true for power MOSFETs?

    <p>Exhibit high speeds of switching</p> Signup and view all the answers

    What is the most important factor for successfully using a firing circuit for multiple thyristors?

    <p>Simultaneous gate current for all thyristors</p> Signup and view all the answers

    What is the primary reason for using a pulse amplifier in a thyristor firing circuit?

    <p>To increase the gate current to required levels</p> Signup and view all the answers

    What happens to the P-layer of a MOSFET when a positive voltage is applied to the gate terminal?

    <p>It becomes an N-layer, allowing current to flow</p> Signup and view all the answers

    In which region does the drain current become approximately independent of the drain to source voltage?

    <p>Saturation region</p> Signup and view all the answers

    What characteristic allows power MOSFETs to avoid excessive breakdown?

    <p>Breakdown voltage being larger than the applied voltage</p> Signup and view all the answers

    Which of the following is NOT an advantage of power MOSFETs?

    <p>High on-state power dissipation</p> Signup and view all the answers

    What structure is an IGBT primarily built upon?

    <p>PNPN structure</p> Signup and view all the answers

    In the construction of an IGBT, what is the role of the P+ substrate?

    <p>It is used for current injection</p> Signup and view all the answers

    What is true about the blocking capacity of power MOSFETs?

    <p>It only blocks high forward voltage and not reverse voltage</p> Signup and view all the answers

    Which application is NOT commonly associated with power MOSFETs?

    <p>NPN transistor amplifiers</p> Signup and view all the answers

    What determines the depth of the induced channel in a MOSFET?

    <p>The voltage at the gate terminal</p> Signup and view all the answers

    Which characteristic is beneficial for thermal stability in power MOSFETs?

    <p>Positive temperature coefficient</p> Signup and view all the answers

    When does a power MOSFET enter the cut-off region?

    <p>When gate-source voltage is much lower than threshold voltage</p> Signup and view all the answers

    What can result from excessive gate voltage application on a power MOSFET?

    <p>Avalanche breakdown</p> Signup and view all the answers

    Which of the following accurately describes the behavior of current in the ohmic region of a power MOSFET?

    <p>Current increases linearly with drain-source voltage</p> Signup and view all the answers

    What is required to protect a power MOSFET from high reverse voltage?

    <p>An additional external diode</p> Signup and view all the answers

    What is the primary role of the gate terminal in a power MOSFET?

    <p>To control current conduction between source and drain</p> Signup and view all the answers

    What does the ID in the equation ID = K (VGS – VT)² represent?

    <p>Drain current</p> Signup and view all the answers

    Which package is NOT commonly associated with power MOSFETs?

    <p>VGA</p> Signup and view all the answers

    What is meant by the term 'drain saturation current' (IDSS)?

    <p>The maximum current that can flow when the gate-source and drain-source voltages are equal</p> Signup and view all the answers

    Which of the following is a characteristic of enhancement MOSFET structures?

    <p>They need a positive gate voltage to conduct</p> Signup and view all the answers

    How is the voltage rating enhanced in an enhancement-type MOSFET?

    <p>By implementing a drift layer</p> Signup and view all the answers

    Which aspect does NOT contribute to the breakdown voltage of a power MOSFET?

    <p>The package type</p> Signup and view all the answers

    What does the term VGS(Off) refer to in power MOSFET specifications?

    <p>The gate-source voltage that results in nearly zero drain current</p> Signup and view all the answers

    Which of the following describes the testing method for an N-channel MOSFET?

    <p>A short circuit is observed when the probe is connected to the drain</p> Signup and view all the answers

    What is the key difference in testing P-channel MOSFETs compared to N-channel MOSFETs?

    <p>The probe colors and connections are the same but reverse the polarities</p> Signup and view all the answers

    In the structure of a n-channel enhancement MOSFET, what is the doping type of the middle layer?

    <p>Lightly doped p-type</p> Signup and view all the answers

    Which is NOT a structure type of power MOSFET mentioned?

    <p>TFT</p> Signup and view all the answers

    Why are power MOSFETs available in various packaging types?

    <p>To accommodate thermal and space constraints</p> Signup and view all the answers

    What primarily causes the increase in drain current (ID) in a power MOSFET?

    <p>Increasing the gate-source voltage (VGS)</p> Signup and view all the answers

    What is the primary advantage of Silicon Controlled Rectifiers in comparison to traditional diodes?

    <p>They can operate at higher voltages.</p> Signup and view all the answers

    How many semiconductor layers are present in a Silicon Controlled Rectifier?

    <p>4 layers</p> Signup and view all the answers

    What type of current does a Silicon Controlled Rectifier allow to pass through it?

    <p>Unidirectional current</p> Signup and view all the answers

    Which of the following applications is primarily suited for Silicon Controlled Rectifiers?

    <p>Power control for electric motors</p> Signup and view all the answers

    What is one of the key roles of a Silicon Controlled Rectifier in power electronics?

    <p>To control high-power delivery in various applications.</p> Signup and view all the answers

    What happens at junction J2 during the Forward Blocking Mode of an SCR?

    <p>It becomes reverse biased.</p> Signup and view all the answers

    Which condition is necessary to transition from Forward Blocking Mode to Forward Conducting Mode?

    <p>A small positive voltage must be applied to the gate terminal.</p> Signup and view all the answers

    In Reverse Blocking Mode, what happens to the current flowing through the SCR?

    <p>No current flows but a small leakage current is observed.</p> Signup and view all the answers

    What is the effect of applying a large forward bias voltage to the SCR during Forward Conducting Mode?

    <p>Avalanche breakdown occurs enhancing current flow.</p> Signup and view all the answers

    What is the role of the gate terminal in the Silicon Controlled Rectifier?

    <p>It controls the flow of current between anode and cathode.</p> Signup and view all the answers

    What occurs in the forward conduction region of an SCR?

    <p>Charge carriers are generated due to collisions in the depletion region.</p> Signup and view all the answers

    What is defined as the voltage at which junction J2 breaks under forward bias?

    <p>Forward breakdown voltage (VBF)</p> Signup and view all the answers

    In the reverse blocking region of an SCR, what is the effect of applying a negative voltage to the anode?

    <p>Leakage current flows due to the forward-biased junction J2.</p> Signup and view all the answers

    Which characteristic describes the TRIAC as a device?

    <p>It is a 3 terminal, bidirectional switch.</p> Signup and view all the answers

    What initiates the conduction in a TRIAC when MT2 is at a positive potential with respect to MT1?

    <p>The two junctions P1-N1 and P2-N2 become forward biased.</p> Signup and view all the answers

    What happens when the applied voltage exceeds the break over voltage in a DIAC?

    <p>The DIAC enters the avalanche breakdown state.</p> Signup and view all the answers

    Which of the following describes the structure of a DIAC?

    <p>It has a five-layer structure resembling two SCRs.</p> Signup and view all the answers

    What is a primary disadvantage of using TRIACs?

    <p>They have non-symmetrical switching characteristics.</p> Signup and view all the answers

    What does the resistor R2 do in a TRIAC control circuit?

    <p>It controls the point of beginning of conduction.</p> Signup and view all the answers

    What is the function of the holding current in a DIAC?

    <p>It keeps the DIAC in the off-state.</p> Signup and view all the answers

    How does a TRIAC control power in an AC circuit?

    <p>By switching on and off during the entire cycle.</p> Signup and view all the answers

    In which quadrant does the DIAC operate when both voltage and current are positive?

    <p>First quadrant</p> Signup and view all the answers

    What is the main use of a DIAC in electrical circuits?

    <p>To trigger TRIACs for better control</p> Signup and view all the answers

    What characteristic of the DIAC helps in reducing harmonics in a system?

    <p>Symmetrical switching characteristics</p> Signup and view all the answers

    What condition must be met for a DIAC to conduct electricity?

    <p>Voltage must exceed a minimum threshold</p> Signup and view all the answers

    In the two transistor analogy of an SCR, what happens when the gate voltage is not applied?

    <p>No current flows through the load</p> Signup and view all the answers

    What occurs during the regeneration process of an SCR upon triggering?

    <p>A self-reinforcing conduction begins</p> Signup and view all the answers

    What happens to an SCR when the anode current falls below the holding current?

    <p>It automatically turns off</p> Signup and view all the answers

    Which of the following indicates the primary limitation of a DIAC?

    <p>Low power handling capability</p> Signup and view all the answers

    Which statement about TRIACs is true regarding their triggering mechanism?

    <p>They require different voltages for forward and reverse cycles</p> Signup and view all the answers

    Which component is essential for triggering the conduction of both halves of the AC cycle in a DIAC circuit?

    <p>The TRIAC</p> Signup and view all the answers

    What occurs when the anode-cathode voltage exceeds the forward break-over voltage in the forward voltage triggering method?

    <p>The SCR gets damaged due to excessive current flow</p> Signup and view all the answers

    Which method of turning ON an SCR involves using a beam of light to activate the device?

    <p>Light triggering</p> Signup and view all the answers

    Why is temperature or thermal triggering not commonly used in practice for SCRs?

    <p>It can lead to thermal runaway and device damage</p> Signup and view all the answers

    In which mode does the dv/dt triggering method enable the SCR to turn ON?

    <p>Forward blocking mode</p> Signup and view all the answers

    What is the primary action that takes place during gate triggering of an SCR?

    <p>Electrons are injected into the P-layer</p> Signup and view all the answers

    Which condition does NOT need to be met for effective gate triggering of an SCR?

    <p>A continuous gate current must be maintained</p> Signup and view all the answers

    What is the main drawback of using the DC triggering method for turning ON an SCR?

    <p>It generates excess heat in the gate</p> Signup and view all the answers

    Which method of turning ON an SCR allows for immediate activation through a transient voltage spike?

    <p>dv/dt triggering</p> Signup and view all the answers

    What happens to junction J2 when the SCR is in the forward blocking mode?

    <p>It is reverse biased and acts as an open circuit</p> Signup and view all the answers

    Study Notes

    Silicon Controlled Rectifier (SCR)

    • Definition: A 3-terminal, 4-layer semiconductor device used to control high power. Often referred to as an SCR diode, 4-layer diode, 4-layer device, or Thyristor.
    • Construction: Made of alternating P and N type semiconductor layers (NPNP or PNPN structures) with 3 junctions (J1, J2, J3).
      • Anode: Positive terminal where conventional current enters.
      • Cathode: Negative terminal where conventional current exits.
      • Gate: Controls the flow of current between the anode and cathode.
    • Modes of Operation:
      • Forward Blocking Mode (Off State): Anode (+) and cathode (-) are biased, gate is open. J1 and J3 are forward biased, J2 is reverse biased. This blocks the majority of current flow (only small leakage current).
      • Forward Conducting Mode (On State): SCR can be turned on by either:
        • Increasing the forward bias voltage beyond the breakdown voltage.
        • Applying a positive voltage to the gate terminal.
      • Reverse Blocking Mode (Off State): Anode (-) and cathode (+) are biased, gate is open. J1 and J3 are reverse biased, J2 is forward biased. Very little current flows due to the reverse bias.
    • V-I Characteristics:
      • Forward Blocking Region: SCR does not conduct current. A small forward leakage current is present.
      • Forward Conduction Region: As the forward bias voltage increases past the breakdown voltage, current increases rapidly. The SCR transitions to the "on" state.
      • Reverse Blocking Region: No current flows until the applied reverse voltage exceeds the reverse breakdown voltage, then an avalanche breakdown occurs and current increases rapidly. This can potentially damage the SCR.

    TRIAC

    • Definition: A 3-terminal AC switch capable of conducting current in both directions. Triggered into conduction by a low energy gate signal. It is a bidirectional thyristor.
    • Construction: Consists of two SCRs in inverse parallel connection with a gate terminal.
      • MT1 and MT2: Terminals for the main current path.
      • Gate (G): Control terminal.
    • Operation: Can be triggered in any of four ways:
      • Positive bias: MT2 (+) and gate (+) with respect to MT1.
      • Positive bias: MT2 (+) with gate (-) with respect to MT1.
      • Negative bias: MT2 (-) and gate (-) with respect to MT1.
      • Negative bias: MT2 (-) with gate (+) with respect to MT1.
    • Characteristics: Has four operating modes corresponding to the four possible voltage polarity combinations of MT2 and gate with respect to MT1.
    • Applications: Commonly used in AC power control, lighting control, and electric motor control.

    DIAC

    • Definition: A 2-terminal bidirectional switch that conducts in both directions when the applied voltage exceeds its breakover voltage. An uncontrolled switch (no gate terminal).
    • Construction: Typically consists of 5 semiconductor layers (2 P-layers and 3 N-layers) with symmetrical structure from each terminal. It can also be constructed with 3 layers (PNP or NPN).
    • Working: Similar to a diode, but conducts in either direction. The middle junction is reverse biased until the breakdown voltage is reached, then it conducts.
    • V-I Characteristics: Operates in the first and third quadrants of the V-I plane. The voltage must exceed the breakover voltage for the DIAC to conduct.
    • Applications: Primarily used for triggering other devices, such as TRIACs, due to its symmetrical switching characteristics.

    DIAC

    • DIAC is a symmetrical device, meaning it conducts in both forward and reverse directions.
    • When the voltage is below the break-over voltage (VBO), the DIAC acts as an open circuit, only allowing a tiny leakage current to pass.
    • When voltage exceeds VBO, the DIAC triggers into the ON-state, allowing current to flow.
    • The voltage across the DIAC then decreases to a steady ON-state voltage.
    • DIACs are ideal for triggering TRIACs.
    • DIACs offer symmetrical switching, which reduces harmonics in a system.
    • They have a low ON-state voltage drop, which increases with voltage.
    • DIACs are easy to switch by increasing or decreasing the applied voltage.
    • DIACs offer smooth power control when used for triggering thyristors and TRIACs.
    • DIACs are low power devices, only conducting above 30 volts and cannot block high voltages.

    Advantages of DIAC

    • Offers symmetrical switching characteristics, reducing system harmonics.
    • Low ON-state voltage drop.
    • Easy switching by voltage variation.
    • Smooth power control for thyristor/TRIAC triggering.

    Disadvantages of DIAC

    • Low power device.
    • Minimum conducting voltage is above 30 volts.
    • Unable to block high voltages.

    Two-Transistor Analogy of SCR

    • An SCR is a semiconductor device that can be turned on and off in a controlled manner.
    • The two-transistor analogy illustrates the working of an SCR by visualizing it as two interconnected transistors.
    • The collector of each transistor is connected to the base of the other.

    SCR Turn ON Mechanism

    • Initially, the SCR's anode is positive, and the cathode is negative, forward biasing the device.
    • Applying a positive voltage pulse to the gate terminal triggers the SCR.
    • The trigger signal initiates conduction by causing a small current flow from anode to cathode.
    • The SCR enters a regenerative process, where the current flow reinforces the triggering effect, leading to latch-up.
    • The SCR becomes fully latched into the ON-state, remaining so even after the gate triggering signal is removed.
    • The SCR conducts until the anode current drops below the holding current, at which point it turns off.
    • The gate triggering signal must be synchronized with the proper timings and voltage levels for reliable turn-on.

    Different Methods for Turning ON SCR

    • An SCR can be turned ON by switching from forward-blocking to forward-conduction mode.
    • Forward Voltage Triggering:
      • Increases anode-cathode voltage to forward break-over voltage.
      • Causes avalanche breakdown at junction J2.
      • Turns the SCR ON.
      • Not recommended in practice due to device damage risk.
    • Light Triggering:
      • Used by light-activated SCRs (LASCRs).
      • A light beam triggers conduction by injecting charge carriers.
    • Temperature/Thermal Triggering:
      • Reverse leakage current increases with temperature, turning ON the SCR.
      • Not used in practice due to overheating risks.
    • dV/dt Triggering:
      • Rapid voltage change across the SCR generates a transient gate current, turning it ON.
      • Spurious voltage spikes can trigger the SCR.
      • Not used in practice due to potential device damage.
    • Gate Triggering:
      • Most commonly used method.
      • Applies a positive voltage between the gate and cathode terminals while the SCR is in forward blocking mode.
      • This injects electrons into the P-layer, reducing the depletion layer in junction J2 and triggering conduction.
      • DC Triggering: Continuous gate signal, high gate losses.
      • AC Triggering: Triggering only during positive half-cycle; phase angle control for firing angle control.
      • Pulse Triggering: Discontinuous signal, reduced gate losses, controllable conduction period; most efficient method.

    Points to Remember for Operating Thyristors

    • Supply voltage should be less than the break-over voltage.
    • Gate signal should make the gate positive with respect to the cathode.
    • To turn OFF a thyristor, anode current should be reduced below the holding current.
    • Once the thyristor is ON, the gate loses control.

    Thyristor Firing Circuits

    • The most common method to turn ON a thyristor is by controlling the gate pulse.
    • The circuit that produces these pulses is called the Firing or Triggering Circuit.
    • These circuits must meet certain conditions for successful triggering.

    Conditions for Triggering Circuits

    • Gate current must be sufficient and flow for the required duration.
    • Voltage pulses should be applied to the driver circuit first and then to the gate-cathode circuit.
    • For circuits with multiple thyristors, each thyristor must be triggered at the appropriate time.

    Types of Thyristor Firing Circuits

    • Resistance Firing Circuit (R-Firing):
      • Simple circuit for controlling firing angle from 0° to 90°.
      • AC supply to the gate terminal for firing.
      • Firing angle control through variable resistance.
      • Advantages: simplicity of operation and firing angle control up to 90°.
      • Disadvantages: limited firing angle, dependence on minimum gate current, temperature sensitivity.
    • Resistance-Capacitance Firing (RC-Firing):
      • Improves firing angle control beyond 0°-90°.
      • Uses a capacitor and a diode to delay gate current.
    • UJT-Firing Circuit:
      • Provides more precise firing angle control.
      • Uses a unijunction transistor (UJT) as a trigger device.

    Power MOSFET

    • Power MOSFETs are designed for high power handling and fast switching speeds.
    • They are widely used in high-frequency applications, like motor drives and power supplies.
    • The operating principle is similar to standard MOSFETs but with higher voltage and current ratings.
    • Available in different structures, most often p-channel and n-channel varieties.
    • Common packages for discrete devices include TO-247, TO-220, D2PAK, and surface mountable SMD-220.
    • Newer packages, like chip-scale devices, PolarPak™, and DirectFET™, are also readily available.

    Operating Principle of Power MOSFET

    • Gate-source voltage (VGS) controls the current between the source and drain terminals.
    • Applying a voltage to the gate creates a channel between the source and drain, allowing current flow.
    • Increasing VGS enhances the channel and increases drain current (ID).
    • The relationship between VGS and drain voltage (VD) depends on device specifics.

    Power MOSFET

    • Drain Current (ID) is determined by the formula: ID = K (VGS – VT)2
      • ID = Drain Current
      • K = Device Constant
      • VGS = Gate Voltage
      • VT = Threshold Voltage
    • Drain Saturation Current (IDSS) is the maximum drain current when the drain-source voltage (VDS) equals the gate-source voltage (VGS).
    • Gate-source Cutoff Voltage (VGS(Off)) is the gate-source voltage value that results in a drain current near zero.
    • Power MOSFETs are tested for conformance to standards:
      • JEDEC JEP 115
      • BS IEC 60747-8-4
      • JEDEC JESD 24

    Power MOSFET Testing

    • N-Channel MOSFET Testing
      • Short the drain and gate terminals to discharge internal capacitance.
      • Place the black probe of a multimeter on the source and the red probe on the drain, an open circuit should be indicated.
      • Move the red probe to the gate then back to the drain, multimeter should indicate a short circuit.
      • This proves the MOSFET is functional.
    • P-Channel MOSFET Testing
      • Follow the same steps as the N-Channel MOSFET testing, but reverse the polarity of the probes.

    Power MOSFET Construction

    • Structure: n+ p n- n+ (n-channel enhancement mode)
      • n+ layers: source and drain
      • p-type layer: body
      • n- layer: drift region (lightly doped)
    • Gate Insulation: oxide layer (silicon dioxide) between the metal and semiconductor.
    • Metal Oxide Semiconductor (MOS) Capacitance: formed by the oxide layer and provides high capacitance (above 1000 pF).

    Power MOSFET Circuit

    • Operation:
      • A positive voltage at the drain relative to the source prevents current flow.
      • A positive voltage at the gate induces a negative charge on the silicon surface.
      • This creates an "induced N layer" in the P-layer, allowing electron flow from drain to source.
      • The gate voltage controls the channel depth and current flow.

    Power MOSFET Characteristics

    • VI Characteristics: Show the relationship between the drain-source voltage (VDS) and drain current (ID).
    • Regions:
      • Cut-off Region: VGS < VT, no current flow.
      • Ohmic Region: Low power dissipation.
      • Saturation Region: Drain current is independent of VDS, dependent on VGS.
    • Breakdown Voltage: Must be higher than the applied voltage to prevent avalanche breakdown.

    Power MOSFET Advantages

    • No second breakdown.
    • Simple gate drive circuit.
    • Easy to switch ON and OFF.
    • High switching frequency.
    • Good thermal stability (positive temperature coefficient).
    • Low on-state resistance.
    • Less expensive.
    • Small size.
    • Voltage-controlled device.
    • Low power required to maintain ON state.
    • Fast switching speed.
    • No extra circuit for commutation.

    Power MOSFET Disadvantages

    • High on-state voltage.
    • High on-state power dissipation.
    • Asymmetric blocking capacity (high forward voltage, low reverse voltage).
    • Susceptible to damage from static electricity.

    Power MOSFET Applications

    • UPS (Uninterruptible Power Supplies)
    • Relay drivers
    • SMPS (Switch Mode Power Supplies)
    • High-frequency inverters
    • Power amplifiers
    • Motor control
    • Display drivers

    Insulated-Gate Bipolar Transistor (IGBT)

    • Construction: PNPN structure with four semiconductor layers.
      • Collector (C) electrode connected to P layer.
      • Emitter (E) electrode between P and N layers.
      • P+ substrate as the base.
      • N- layer for PN junction J1.
      • P regions for PN junction J2
      • N+ region for emitter and gate connections.
      • Oxide layer isolates gate from the semiconductor.

    IGBT Equivalent Structure

    • Equivalent Model: combination of an N-channel MOSFET and a PNP BJT in Darlington configuration.
    • Two Current Paths:
      • Collector, P+ substrate, N-, P, emitter.
      • Collector, P+ substrate, N-, P, N+, emitter.

    IGBT Working

    • OFF State:
      • Gate voltage (VG) = 0V.
      • Junction J1 forward biased, J2 reverse biased.
      • No current flows between collector and emitter.
    • ON State:
      • Positive VG applied to gate.
      • Negative charges accumulate beneath gate oxide.
      • When VG exceeds threshold voltage, an "induced N channel" forms.
      • Electrons flow from emitter to collector via the drift region.
      • This reduces the resistance of the drift region, turning on the IGBT.

    IGBT Types

    • Punch-Through IGBT (Asymmetrical):
      • Includes an N+ buffer layer.
      • Asymmetric voltage blocking characteristics (higher forward breakdown voltage than reverse).
      • Fast switching speed.
      • Used in DC circuits (inverters, choppers).
    • Non-Punch-Through IGBT (Symmetrical):
      • No N+ buffer layer.
      • Symmetric breakdown voltage characteristics.
      • Used in AC circuits.

    IGBT V-I Characteristics

    • Transfer Characteristics: Relation between VGE and IC.
      • VGE < VGET (threshold voltage): device is OFF, only leakage current.
      • VGE > VGET: device turns ON, IC increases proportionally to VGE.

    IGBT Advantages

    • Combines advantages of both BJT and MOSFET.
    • High voltage and current handling capabilities.
    • High input impedance.
    • Low input current and losses.
    • Simple and inexpensive gate drive circuitry.
    • Low on-state resistance.
    • High current density (small chip size).
    • Higher power gain than BJT and MOSFET.
    • Faster switching speed than BJT.

    IGBT Disadvantages

    • Lower switching speed than MOSFET.
    • Unidirectional (cannot conduct in reverse).
    • Cannot block high reverse voltage.
    • Costlier than BJT and MOSFET.
    • Latching problems can occur.

    IGBT Applications

    • SMPS (Switched Mode Power Supplies)
    • UPS (Uninterruptible Power Supply)
    • AC and DC motor drives
    • Choppers and inverters
    • Solar inverters

    Silicon Controlled Rectifier (SCR)

    • An SCR is a three-terminal, four-layer semiconductor device that controls high power.
    • It is unidirectional, conducting current in one direction only, like a diode.
    • Constructed with alternating P and N-type semiconductor layers, creating three junctions (J1, J2, J3).
    • Terminals: Anode (A), Cathode (K), and Gate (G).
    • The gate terminal controls the flow of current between the anode and cathode.

    SCR Operating Modes

    • Forward Blocking (Off State):
      • Anode (+) and Cathode (-) are biased, gate is open.
      • J1 and J3 are forward biased, J2 is reverse biased.
      • Depletion region at J2 acts as a barrier, blocking current flow.
      • Only a small leakage current flows.
      • SCR conducts when the voltage reaches its breakdown value.
    • Forward Conducting (On State):
      • SCR can conduct when the anode-cathode voltage exceeds the breakdown voltage or a positive voltage is applied to the gate.
      • Increasing voltage beyond the breakdown point causes a large number of charge carriers, allowing for conduction.
      • Applying a positive gate voltage forward biases J2, narrowing the depletion region, enabling current flow.
    • Reverse Blocking (Off State):
      • Anode (-) and Cathode (+) are biased, gate is open.
      • J1 and J3 are reverse biased, J2 is forward biased.
      • No significant current flows, only reverse leakage current.

    SCR V-I Characteristics

    • Divided into three regions: forward blocking, forward conduction, and reverse blocking.
    • Forward Blocking Region:
      • Small leakage current flows as the SCR doesn't conduct significantly.
    • Forward Conduction Region:
      • Current flows rapidly when the SCR switches from blocking to conduction mode.
      • The voltage across the SCR drops significantly.
    • Reverse Blocking Region:
      • Very little current flows, similar to the forward blocking region.
      • If reverse voltage increases beyond the breakdown point, the SCR can be damaged.

    TRIAC (Triode for Alternating Current)

    • A three-terminal AC switch that conducts in both directions.
    • Controlled by low-energy gate signals.
    • A bi-directional device, meaning it can conduct current regardless of the voltage polarity across its terminals.
    • Composed of two SCRs in an inverse parallel connection with a common gate terminal.
    • Used in power electronics to control alternating current.

    DIAC (Diode for Alternating Current)

    • A two-terminal, bi-directional switch that conducts in both directions when the applied voltage exceeds its break-over voltage.
    • Essentially an uncontrolled switch with no gate terminal for control.
    • Used for triggering other devices, specifically TRIACS, due to its symmetrical switching characteristics.
    • Constructed as two anti-parallel SCRs without a gate terminal.
    • It only operates in the 1st and 3rd quadrants of its V-I characteristic curve.

    DIAC

    • DIAC is a symmetrical device, meaning the graph of its voltage and current relationship is symmetrical in both quadrants, forming the shape of a 'Z'.
    • When voltage is below the breakover voltage (VBO), the DIAC blocks current except for leakage current, remaining in the OFF state.
    • As voltage rises above VBO, the DIAC triggers into the ON state, and current increases.
    • The voltage across the device then reduces to a steady ON state voltage.
    • The DIAC operates similarly in the third quadrant, with the only difference being that the voltage and current are reversed.

    DIAC Advantages

    • Offers symmetrical switching characteristics, reducing harmonics in a system.
    • Has a low on state voltage drop, which increases with voltage.
    • Easily switched by increasing or decreasing the applied voltage.
    • Provides smooth power control when used to trigger other thyristors and TRIACs.

    DIAC Disadvantages

    • It is a low power device.
    • It conducts only when voltage increases above 30 volts.
    • It cannot block high voltages.

    DIAC Applications

    • The main application of DIAC is to trigger TRIACs.
    • TRIACs have asymmetrical triggering due to differences in their structure, resulting in uneven triggering for forward and reverse currents.
    • This asymmetry creates harmonics.
    • The DIAC is connected in series with the gate of the TRIAC, offering symmetrical triggering.
    • Since the DIAC switches on at the same voltage for both directions, it ensures symmetrical triggering of the TRIAC for both halves of the AC cycle.
    • DIACs are not suitable for regulating power on their own but are used with TRIACs to regulate high power circuits in applications like motor speed control, heat control, and dimmers.

    Two Transistor Analogy of SCR

    • The SCR can be understood as a combination of two interconnected transistors.
    • The collector of each transistor is connected to the base of the other transistor.
    • The two transistor analogy helps explain how the SCR conducts when triggered.
    • The SCR is in the OFF state when the base current of transistor 2 is zero.
    • When a small voltage is applied to the gate and cathode, the base current of transistor 1, which is the same as the collector current of transistor 2, drives both transistors into saturation mode.

    SCR Turn ON Mechanism

    • An SCR or thyristor is a semiconductor device that can be turned on and off in a controlled manner.
    • To turn on the SCR, a triggering signal is applied to the gate terminal.
    • The SCR enters a conducting state, and remains on until the current falls below a certain threshold.

    Key steps:

    • Forward Biasing: The anode is connected to positive voltage and the cathode to negative voltage, which forward biases the device.
    • Gate Triggering Signal: A positive voltage pulse is applied to the gate terminal, activating the SCR.
    • Initiation of Conduction: The signal causes a small current flow from anode to cathode, triggering the SCR.
    • Regeneration Process (Positive Feedback): The small current reinforces the triggering effect, leading to further conduction.
    • Latch-Up: The regenerative process continues until the SCR is fully latched into the conducting state.
    • Maintained Conduction: The SCR remains on until the anode current drops below the holding current, at which point it turns off.

    Methods For Turning ON SCR

    • SCR's operation can be analyzed in three modes: forward blocking, forward conduction, and reverse blocking.
    • Forward Voltage Triggering: This method is not recommended as it can damage the device due to excessive current flow beyond the breakdown voltage.
    • Light Triggering: Used with LASCRs (light-activated SCRs). Applying a light beam of specific wavelength and frequency to the inner P-layer injects charge carriers, turning on the SCR.
    • Temperature or Thermal Triggering: This method is not practical because it relies on a high leakage current due to increasing temperature, which can lead to thermal runaway.
    • dV/dt Triggering: A high rate of voltage rise across the SCR can create sufficient gate current, turning it on. This effect is not intentional but can lead to unwanted SCR triggering.
    • Gate Triggering: The most reliable and efficient method. Applying a positive voltage between the gate and cathode while the anode is forward-biased turns on the SCR.

    Gate Triggering Methods

    • DC Triggering: Continuous DC supply applied to the gate, which leads to higher gate losses.
    • AC Triggering: AC supply is used for triggering, turning on the SCR only during the positive half-cycle. The triggering angle can be controlled by adjusting the phase angle.
    • Pulse Triggering: Short pulses are applied to the gate, minimizing gate losses and allowing control over the conduction period. This method is widely used.

    SCR Turn OFF Mechanism

    • The SCR can be turned OFF by reducing the anode current below the holding current.

    Triggering or Firing Circuits of Thyristors

    • The circuit used to turn on a thyristor by providing gate pulses is called a "Firing or Triggering Circuit".
    • The most commonly used triggering circuits are: Resistance Firing Circuit (R-Firing), Resistance-Capacitance Firing (RC-Firing), and UJT-Firing Circuit.

    Power MOSFET

    • Power MOSFET is a type of MOSFET designed to handle high levels of power.
    • These devices feature high switching speeds and are available in various structures like: VDMOS, DMOS, Trench-MOS, and VMOS.
    • Power MOSFETs are used in integrated circuits and come in various packages including: SOIC, TO-247, TO-220, D2PAK, and SMD-220.

    Power MOSFET Operating Principle

    • Power MOSFETs operate similarly to normal MOSFETs.

    • Applying a voltage to the gate terminal creates a channel between the source and drain terminals, allowing current flow.

    • Increasing the gate-source voltage (VGS) enhances the channel and increases the drain current (ID).

    • The relationship between gate and drain voltages is crucial for power MOSFET operation.### Power MOSFETs

    • Drain Current (ID) is proportional to the square of the difference between gate voltage (VGS) and threshold voltage (VT).

    • Device Constant (K) is a property of a specific MOSFET and influences drain current.

    • Gate-Source Cutoff Voltage (VGS(Off)) is the gate-source voltage where drain current is near zero.

    • Drain Saturation Current (IDSS) is the maximum drain current when VDS=VGS.

    • Power MOSFET Testing can be done with a multimeter, checking for continuity using different probe placements on the drain, gate and source.

    • Power MOSFET Structure features a vertical structure of n+ p n- n+ layers for n-channel MOSFETs.

    • Drift Region (n-) within the power MOSFET structure determines the breakdown voltage.

    • Metal Oxide Semiconductor Capacitance exists at the gate due to the oxide layer between the gate terminal and the semiconductor.

    • Power MOSFET Circuit utilizes the flow of current from drain to source, controlled by gate voltage.

    • Power MOSFET Characteristics are characterized by three regions: cut-off, ohmic and saturation.

    • Cut-off Region occurs when VGS is less than VT, and the MOSFET is off.

    • Ohmic Region has low power dissipation.

    • Saturation Region allows the MOSFET to operate as a switch.

    • Advantages of Power MOSFETs:

      • High-frequency operation
      • Low on-state resistance
      • Thermal stability
      • Fast switching speed
      • Simple gate driving circuit
      • Small size and cost-effectiveness

    • Disadvantages of Power MOSFETs:

      • High on-state voltage
      • Asymmetry in blocking capabilities
      • Susceptibility to damage from static electricity

    Insulated Gate Bipolar Transistors (IGBTs)

    • IGBT Construction features a four-layer PNPN structure.
    • Collector (C) is attached to the P layer.
    • Emitter (E) is attached between the P and N layers.
    • Gate (G) is insulated with a SiO2 layer.
    • Drift Region (N-) in the IGBT structure is thicker for higher voltage blocking capacity.
    • Punch Through IGBT includes an N+ buffer layer, has asymmetric voltage blocking capabilities and faster switching speed.
    • Non-Punch Through IGBT lacks the N+ buffer layer, has symmetrical blocking capabilities and is suitable for AC applications.
    • IGBT Working Principles rely on biasing between gate-emitter and collector-emitter terminals, forming a channel for electron flow.
    • IGBT V-I Characteristics showcase the relationship between VGE, IC, and VCE, demonstrating the controlled current flow.
    • Advantages of IGBTs:
      • High voltage and current handling capabilities
      • High input impedance
      • Simple gate drive circuit
      • Fast switching speed
      • Low on-state resistance
    • Disadvantages of IGBTs:
      • Lower switching speed than MOSFETs
      • Unidirectional current flow
      • Susceptibility to latching issues
      • Higher cost
    • Applications of IGBTs:
      • SMPS (Switched Mode Power Supply)
      • UPS (Uninterruptible Power Supply)
      • Motor drives
      • Inverters
      • Solar inverters

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    This quiz explores the fundamentals of Silicon Controlled Rectifiers (SCR), a key component in power electronics. You'll learn about its structure, operational modes, and the roles of its terminals. Test your understanding of this crucial semiconductor device used in controlling high power applications.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser