Intuitive explanation of SiC MOSFET thermal impedance, SOA, and LTspice simulation

00:24:36
https://www.youtube.com/watch?v=Ixg198eJSMg

概要

TLDRThe presentation titled "Intuitive Explanation of Silicon Carbide Thermal Impedance, Safe Operating Area, and MPI Simulation" by Samanyakov addresses the thermal management issues related to the junction temperature of transistors. It uses a thermal equivalent circuit to model the thermal behavior similar to an electric circuit. The goal is to explore the linear mode not the switching mode of a transistor. The presentation details a method of using capacitors as thermal capacitances for understanding heat absorption. It looks into the Safe Operating Area (SOA) plot that helps determine the boundary conditions to avoid exceeding the junction temperature limits during operation. Emphasizing transient thermal behavior, the presenter demonstrates using thermal impedance plots to manage thermal resistance during pulses and highlights the importance of simulations in accurately predicting junction temperatures. The speaker notes discrepancies in maximum junction temperature specifications by manufacturers and introduces utilizing models for effective simulation and analysis of thermal resistance trends and their impact on transistor operation.

収穫

  • 🖥️ Presentation focuses on silicon carbide thermal impedance and safe operating areas.
  • 🔄 Thermal behavior of transistors is modeled using equivalent circuits.
  • ⚡ Linear mode of transistor operation is explored, not switching mode.
  • 📉 Safe Operating Area (SOA) plot determines safe boundaries for transistors.
  • 🌡️ Thermal capacitors represent transient heat absorption in the model.
  • 💡 Thermal impedance plot helps compute temperature rise during pulse operations.
  • 🎥 Simulation models provide insight into varying current profiles for temperatures.
  • 🔍 Discrepancies found between simulations and manufacturer specifications.
  • 📊 Allows for probing junction temperatures using simulation models in Multisim.
  • ✅ Importance of integrating thermal equivalents into models for accurate predictions.

タイムライン

  • 00:00:00 - 00:05:00

    In this presentation, the speaker addresses the thermal problems of transistors, particularly focusing on the junction temperature. The presentation uses an equivalent thermal circuit to emulate thermal behavior in electrical terms. The primary focus is on the linear mode of operation in transistors, rather than the switching mode. The speaker explains various aspects of thermal resistance and capacitance, representing junction and case temperatures, and discusses the need for a distributed model, emphasizing the propagation of heat throughout the transistor, similar to a three-dimensional thermal transmission line.

  • 00:05:00 - 00:10:00

    The concept of the Safe Operating Area (SOA) plot is introduced, which provides data about the transient behavior of junction temperatures through a plot of current vs voltage. The boundaries of the SOA plot define the maximum voltage and current that a transistor can handle. The speaker discusses silicon carbide devices and the difference in maximum operating temperatures between manufacturers, noting how these plots can be used to assess safe junction temperatures under pulsed conditions.

  • 00:10:00 - 00:15:00

    The speaker explains the importance of thermal impedance plots, which account for the transient nature of temperature due to pulses and help in determining the maximum temperature. The thermal impedance changes based on pulse width and is used to find the right junction temperature under various pulse conditions. The speaker discusses the difference in thermal resistance values for different pulse durations, emphasizing that shorter pulses have lower thermal resistance.

  • 00:15:00 - 00:24:36

    Simulation setups are discussed, where electronic models are used to mimic transistor behavior with a focus on linear operation. Using the plots and models discussed, the speaker identifies discrepancies in expected junction temperatures and the limitations of the SOA in real-world applications. The conclusion is that, despite discrepancies, the simulations and data are effective for educational purposes, aiding in better understanding of thermal impacts on semiconductor devices.

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よくある質問

  • What is the main focus of this presentation?

    The main focus is on silicon carbide thermal impedance, safe operating area, and simulations using thermal equivalent circuits.

  • Why use a thermal equivalent circuit?

    A thermal equivalent circuit is used to emulate the thermal behavior of a transistor, representing power dissipation via an electrical circuit.

  • What is the significance of the safe operating area (SOA) plot?

    The SOA plot helps to determine the conditions under which a transistor can operate safely without exceeding the maximum junction temperature.

  • Why are thermal capacitances important?

    Thermal capacitances are crucial for considering transient heat absorption during pulse operations, affecting how temperature rises.

  • What does the thermal impedance plot indicate?

    The thermal impedance plot indicates transient thermal resistance to help find maximum temperatures due to pulses.

  • How does junction temperature change during pulse operation?

    Junction temperature rises to different points depending on pulse width and power, rather than steadily, because of transient heat absorption.

  • What limitations exist with single pulse and pulse train methods for temperature calculation?

    These methods assume specific thermal behaviors and may not accurately predict temperatures under arbitrary pulse profiles.

  • How can simulation models improve temperature analysis?

    Simulation models incorporating thermal circuits allow for more precise temperature predictions across varying current profiles.

  • What discrepancy was discussed regarding manufacturer specifications?

    There was a discrepancy between simulated maximum junction temperatures and manufacturer-specified safe operating limits.

  • What tools and simulations are explored in this presentation?

    The presentation uses simulations in Multisim to explore linear modes in transistors using silicon carbide.

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  • 00:00:00
    hi I'm samanyakov this presentation is
  • 00:00:03
    entitled intuitive explanation of
  • 00:00:05
    silicon carbide thermal impedance safe
  • 00:00:08
    operating area and empty spy simulation
  • 00:00:11
    there is a disclaimer here that the
  • 00:00:14
    devices and simulation tools shown in
  • 00:00:16
    this presentation are for educational
  • 00:00:19
    purposes and only there is no
  • 00:00:22
    endorsement or recommendation implied
  • 00:00:25
    the issue that I'm addressing in this
  • 00:00:28
    presentation is the thermal problem of a
  • 00:00:33
    transistor and in particular The
  • 00:00:35
    Junction temperature
  • 00:00:37
    so here is an equivalent circuit a
  • 00:00:39
    thermal equivalent circuit in which the
  • 00:00:42
    thermal behavior is emulated by an
  • 00:00:45
    electrical circuit in this case the
  • 00:00:48
    current Source represent the power which
  • 00:00:50
    is pumped into the transistor that is
  • 00:00:53
    the voltage and current through it and
  • 00:00:56
    I'm primarily interested in this
  • 00:00:58
    presentation in the linear mode
  • 00:01:01
    inductive not the switching mode the
  • 00:01:04
    transistor is completely on and there is
  • 00:01:06
    the earlier Zone but rather when you
  • 00:01:08
    have a voltage across the transistor any
  • 00:01:11
    current passing through it so this will
  • 00:01:14
    represent the power dissipated within
  • 00:01:17
    the unit these are the thermal
  • 00:01:20
    resistances
  • 00:01:22
    this is the junction temperature is
  • 00:01:25
    represented by the voltage here
  • 00:01:27
    case temperature is the voltage here and
  • 00:01:31
    this is the thermal resistance between
  • 00:01:33
    Junction and case also I'm showing here
  • 00:01:37
    the thermal resistance between the case
  • 00:01:40
    and ambient
  • 00:01:41
    and then we have the ambient temperature
  • 00:01:44
    represented by a clamped by a voltage
  • 00:01:48
    source now these capacitors represent
  • 00:01:52
    thermal capacitances and that is the
  • 00:01:55
    amount of heat that is absorbed by the
  • 00:01:58
    mass you need it for transient in DC you
  • 00:02:02
    don't need it that is for steady state
  • 00:02:04
    you don't need it because you just
  • 00:02:06
    consider the resistance but if you have
  • 00:02:10
    a pulse coming in then temperature
  • 00:02:13
    starts rising and some of the heat is
  • 00:02:15
    being absorbed by the mass so this
  • 00:02:18
    capacitors represent the
  • 00:02:21
    terminal capacitances within the area of
  • 00:02:24
    the dye and the structure as a matter of
  • 00:02:27
    fact there is a need for a distributed
  • 00:02:30
    presentation because the heat is
  • 00:02:33
    propagating throughout the die you might
  • 00:02:36
    say it's like a three-dimensional
  • 00:02:38
    thermal transmission line and therefore
  • 00:02:42
    the best way is of course to use this
  • 00:02:45
    the leather type of a presentation
  • 00:02:48
    although some cases you can get by by a
  • 00:02:51
    simpler structure so with this
  • 00:02:55
    equivalent circuit you can probe into
  • 00:02:57
    the issue of the junction temperature in
  • 00:03:01
    the case that you have a current with
  • 00:03:03
    some background current and there is a
  • 00:03:05
    pulse and then some more current and the
  • 00:03:08
    pulse or any other profile of a car
  • 00:03:11
    manufacturers are giving in the data
  • 00:03:14
    sheet information regarding the
  • 00:03:16
    transient behavior of the junction
  • 00:03:19
    temperature and one of them is they save
  • 00:03:22
    operating area plot which is shown here
  • 00:03:25
    and let me go over it very quickly the
  • 00:03:28
    y-axis is current the drain current the
  • 00:03:31
    x-axis is the drain to Source voltage
  • 00:03:33
    this device is a 1200 volt device
  • 00:03:38
    silicon carbide 25 million quite a hefty
  • 00:03:43
    transistor and then we have boundaries
  • 00:03:45
    here this
  • 00:03:47
    right boundary is actually the maximum
  • 00:03:50
    voltage that you can expose the
  • 00:03:53
    transistor to 1200 volt and then there
  • 00:03:57
    is a upper boundary which is the maximum
  • 00:04:00
    current and then this boundary here is
  • 00:04:03
    actually the RDS on because if the
  • 00:04:06
    voltage is low you cannot go above
  • 00:04:10
    certain currents which are limited by
  • 00:04:12
    the resistance of the S1 okay so in fact
  • 00:04:16
    each point here represents a ratio
  • 00:04:19
    between voltage and current to give you
  • 00:04:22
    the audio song so this is this boundary
  • 00:04:25
    here and then we have these curves here
  • 00:04:28
    and these are four pulses so if I have a
  • 00:04:31
    pulse of say 100 microseconds
  • 00:04:35
    in order to be in the safe
  • 00:04:38
    Junction temperature you have to be
  • 00:04:40
    below this line meaning that the
  • 00:04:42
    boundary here let's say take for example
  • 00:04:45
    if the voltage of the transistor is 100
  • 00:04:48
    volt then
  • 00:04:51
    you can have a current of the pulse of
  • 00:04:55
    the 100 microsecond of about I'd say 50
  • 00:05:00
    M okay so as long as you are below this
  • 00:05:05
    line you are okay if you are about this
  • 00:05:08
    line you are supposed to
  • 00:05:09
    violate this maximum Junction
  • 00:05:12
    temperature unfortunately Cree does not
  • 00:05:15
    give you what is the maximum Junction
  • 00:05:20
    temperature for these curves
  • 00:05:22
    well the maximum Junction temperature
  • 00:05:24
    for the transistor of 3 wolf speed is
  • 00:05:29
    150 degree so you might have thought
  • 00:05:33
    that this is 150 degrees well we'll
  • 00:05:36
    check it later on on the other hand some
  • 00:05:38
    windows like St of course also give this
  • 00:05:41
    safe operating area plot in their data
  • 00:05:44
    sheet and then this particular unit that
  • 00:05:47
    they have the silicon carbide has
  • 00:05:50
    specified the maximum operating
  • 00:05:53
    temperature of 200 Centigrade as opposed
  • 00:05:58
    to 150 for world speed I I really don't
  • 00:06:01
    understand the very big difference in
  • 00:06:04
    any event
  • 00:06:05
    regarding our discussion here they are
  • 00:06:08
    showing the maximum temperature for
  • 00:06:11
    these plots that they're saying okay
  • 00:06:13
    these plots are for a maximum of 200
  • 00:06:18
    degrees and of course we have the same
  • 00:06:20
    situation here we've got different
  • 00:06:22
    pulses of different width however this
  • 00:06:26
    safe operating area is is good for the
  • 00:06:29
    boundary but does not give you
  • 00:06:32
    information of say suppose you have a
  • 00:06:35
    100 microsecond pulse okay and let's say
  • 00:06:39
    they
  • 00:06:40
    voltage across the transistor is 100
  • 00:06:43
    volt what is the junction temperature
  • 00:06:45
    well you don't get it from here what you
  • 00:06:48
    get here is that you can go up to a
  • 00:06:51
    current of this value but what about
  • 00:06:54
    this case this current you just don't
  • 00:06:58
    have this information here you can get
  • 00:07:01
    it from this plot which is the thermal
  • 00:07:04
    impedance
  • 00:07:05
    and what it is it sort of takes into
  • 00:07:10
    account the fact that if you have pulses
  • 00:07:13
    the temperature are not of course
  • 00:07:15
    stabilized but they are sort of a
  • 00:07:18
    transient temperature and this will help
  • 00:07:21
    you to find out what is the maximum
  • 00:07:23
    temperature due to pulses so
  • 00:07:27
    let's just go over it very quickly in
  • 00:07:30
    general and then I'll probe into it a
  • 00:07:32
    little bit more in depth what we have
  • 00:07:35
    here this is the thermal impedance that
  • 00:07:38
    is the thermal resistance during
  • 00:07:41
    transient this is the meaning of this
  • 00:07:43
    thing this is the pulse
  • 00:07:46
    width okay so we have one microsecond up
  • 00:07:49
    to 100 milliseconds and here I'm
  • 00:07:52
    concentrating now on one
  • 00:07:55
    curve here which is the Single part this
  • 00:07:58
    is the curve okay it goes up and then it
  • 00:08:00
    sort of clamps to this value which is
  • 00:08:04
    the DC thermal resistance between
  • 00:08:07
    Junction and K so this is what is given
  • 00:08:10
    is the data sheet as The Junction to
  • 00:08:13
    case thermal resistance in this
  • 00:08:15
    particular case for this particular
  • 00:08:17
    transistor it's 0.24 degrees per watt
  • 00:08:22
    okay but if the pulses are short if the
  • 00:08:26
    pulses are short not long passes for
  • 00:08:30
    example 100 microsecond where at this
  • 00:08:34
    point and at this point we have a
  • 00:08:36
    certain value okay so this would be like
  • 00:08:39
    uh 20 10 to the 10 to the minus
  • 00:08:43
    3.03 okay so this will be the value here
  • 00:08:47
    what does it mean it means that if the
  • 00:08:51
    pulse is short then the thermal
  • 00:08:56
    resistance that you have to take into
  • 00:08:58
    account is not this wonderful steady
  • 00:09:00
    state but rather they want for this
  • 00:09:03
    particular case of the width of the
  • 00:09:06
    pulse
  • 00:09:08
    and then we're talking here about a
  • 00:09:12
    single path okay so this is this curve
  • 00:09:15
    here we'll talk about these later on so
  • 00:09:17
    let's have a look what is the meaning of
  • 00:09:19
    this single pulse line here or curve
  • 00:09:23
    here okay so let's assume that we have a
  • 00:09:26
    pulse of a power injected into the
  • 00:09:30
    transistor okay this is the pause
  • 00:09:32
    hundred microsecond width and there's a
  • 00:09:35
    second height for the power
  • 00:09:38
    now obviously the temperature will start
  • 00:09:40
    going up
  • 00:09:42
    if this pulse is much longer we are in
  • 00:09:47
    the continuous steady state situation
  • 00:09:49
    and then of course they
  • 00:09:53
    temperature of the junction or Junction
  • 00:09:55
    to case will be the power times the
  • 00:09:58
    thermal resistance between Junction and
  • 00:10:01
    K however if the pulse is short
  • 00:10:04
    temperature will rise only to this point
  • 00:10:07
    okay so obviously uh just the power
  • 00:10:10
    times the steady state thermal
  • 00:10:13
    resistance is incorrect it has to be
  • 00:10:15
    shorter this is exactly this line I have
  • 00:10:18
    to sort of Mark this as the thermal
  • 00:10:22
    resistance Junction to case for pulse
  • 00:10:24
    okay so this pulse is 10 microsecond and
  • 00:10:29
    for 10 microsecond the value of this
  • 00:10:32
    thermal resistance pulse is seven Milli
  • 00:10:36
    degree pair what as opposed to
  • 00:10:40
    240 Milli degree
  • 00:10:43
    Centigrade per Watts so it's a much much
  • 00:10:46
    lower one
  • 00:10:48
    thermal resistance because it only got
  • 00:10:51
    to this point so when you multiply the
  • 00:10:54
    power by this value from this curve
  • 00:10:57
    you'll get the right Junction
  • 00:11:00
    temperature
  • 00:11:01
    if the pulse is wider then you'll get to
  • 00:11:06
    a higher point and obviously you have to
  • 00:11:09
    look at the corresponding pulse width
  • 00:11:13
    which is 100
  • 00:11:14
    micro second it'll be here and this will
  • 00:11:18
    be 21 and this will be this point here
  • 00:11:21
    so this is the meaning of this plot
  • 00:11:24
    which is very neat for a single part
  • 00:11:26
    however if you have a train of pulses
  • 00:11:30
    that is you have some frequency with
  • 00:11:34
    pulses of certain width then you have to
  • 00:11:37
    go to this area here and let me go over
  • 00:11:40
    it quickly here in this case we have the
  • 00:11:44
    pulses coming in now obviously for this
  • 00:11:48
    first one we got up to here but if this
  • 00:11:51
    train persists eventually we'll get to a
  • 00:11:54
    higher temperature
  • 00:11:56
    and this temperature now depends on the
  • 00:11:59
    average power as well as the duty cycle
  • 00:12:02
    because of course the if the due to
  • 00:12:04
    cycle is large then it will go to a
  • 00:12:07
    higher value okay so here are the plots
  • 00:12:10
    now that allow you to estimate this
  • 00:12:14
    temperature for the train of pulses
  • 00:12:17
    now the weight is specified here is this
  • 00:12:22
    is still the width of the pulse this is
  • 00:12:25
    this width here and this curves now are
  • 00:12:28
    for the duty cycle okay so for any given
  • 00:12:32
    duty cycle you have to look for the
  • 00:12:35
    corresponding curve here so say if it is
  • 00:12:38
    10 microsecond pulse with the duty cycle
  • 00:12:43
    of let's say
  • 00:12:46
    0.01 then this will be this value
  • 00:12:48
    however
  • 00:12:50
    if you have
  • 00:12:52
    a current of another profile not a
  • 00:12:55
    single pulse and not a train of pulses
  • 00:12:58
    which are starting from zero you cannot
  • 00:13:01
    get the junction temperature problem
  • 00:13:04
    plots that I've shown not the safe
  • 00:13:07
    operating area and not the thermal
  • 00:13:10
    impedance okay for this you need this
  • 00:13:14
    equivalent circuit or this
  • 00:13:16
    presentation which will give you for any
  • 00:13:21
    profile The Junction temperature okay
  • 00:13:23
    you cannot get it from here and you
  • 00:13:27
    cannot get it from here this is just the
  • 00:13:30
    limit
  • 00:13:31
    for a single pulse
  • 00:13:33
    and here this is the you get a
  • 00:13:36
    temperature for a train of pulses not
  • 00:13:40
    any arbitrary current profile so you
  • 00:13:43
    need
  • 00:13:44
    this equivalent circuit
  • 00:13:46
    some vendors will give it as a separate
  • 00:13:49
    unit that you can sort of during
  • 00:13:52
    simulation find out what is the
  • 00:13:55
    instantaneous power and you get this
  • 00:13:57
    value or
  • 00:14:00
    some vendors and we see more and more
  • 00:14:04
    vendors are giving
  • 00:14:07
    a model of a transistor that includes
  • 00:14:10
    this equivalent circuit so here is an
  • 00:14:15
    example this is just one example as I've
  • 00:14:17
    said other
  • 00:14:19
    manufacturers are providing similar
  • 00:14:21
    models and this is for Wall Street the
  • 00:14:25
    free and here I am showing a transistor
  • 00:14:29
    this is this one this third 25 million
  • 00:14:33
    1200 volt voltage
  • 00:14:36
    and you just put it in as a regular
  • 00:14:40
    model of in this case entity spice and
  • 00:14:44
    the difference is that now you're
  • 00:14:46
    getting two outputs additional outputs
  • 00:14:50
    one is the case temperature in one of
  • 00:14:53
    the junction temperature these are
  • 00:14:55
    coming
  • 00:14:57
    out of here
  • 00:14:59
    now in order to examine the linear case
  • 00:15:03
    linear operational mode
  • 00:15:06
    I've set up this circuit to be a current
  • 00:15:10
    source and this is done by having this
  • 00:15:12
    resistor here now if I have an input
  • 00:15:15
    pulse say of 10 volt
  • 00:15:17
    and if this transfer starts to conduct
  • 00:15:21
    and then it will lock at the threshold
  • 00:15:26
    voltage between gated force and let's
  • 00:15:29
    say that the threshold voltage is a say
  • 00:15:31
    4 volt then the remaining 10 minus 4 6
  • 00:15:35
    voltage on this resistor being one ohm
  • 00:15:39
    you'll have a 6 amp passing through the
  • 00:15:43
    current while the voltage is of course
  • 00:15:46
    the Thousand volt here which is the
  • 00:15:48
    voltage source minus the voltage here
  • 00:15:50
    which is six volt in this particular
  • 00:15:52
    cave you can neglect it or take it into
  • 00:15:54
    account okay so this is just a tool to
  • 00:15:58
    see how well if this model operates
  • 00:16:02
    so in this case I'm feeling a pulses
  • 00:16:06
    here of 10 volt to the gate
  • 00:16:10
    in the width of the pulse is 10
  • 00:16:13
    microseconds and the period is 100
  • 00:16:17
    microseconds meaning that we have a duty
  • 00:16:20
    cycle of 10 to 100.1 okay
  • 00:16:25
    due to cycle does not need to be entered
  • 00:16:28
    here I'm just taking it as a reference
  • 00:16:31
    for comparison later on
  • 00:16:33
    so in this case I've clamped this case
  • 00:16:38
    to 25 degree which is like representing
  • 00:16:43
    the ambient temperature exactly as I put
  • 00:16:46
    it here
  • 00:16:48
    this is the terminal of the case I don't
  • 00:16:52
    have a thermal resistance between case
  • 00:16:55
    and ambient because I'm assuming as in
  • 00:16:58
    most data sheets that the case is kept
  • 00:17:03
    constant clamped to 25 degrees so this
  • 00:17:07
    resistance is zero okay so this goes
  • 00:17:11
    directly to this clamping temperature
  • 00:17:15
    of course if I would have had a heatsink
  • 00:17:17
    and I would have known the thermal
  • 00:17:20
    resistance of the heatsink I could have
  • 00:17:22
    put here a resistor okay but in this
  • 00:17:25
    case I'm just examining parameters
  • 00:17:28
    against the data sheet and most of the
  • 00:17:30
    parameters in the data chips are given
  • 00:17:33
    for a case temperature of 25 degrees or
  • 00:17:36
    some other and here is what I'm getting
  • 00:17:38
    and you can see we see first of all the
  • 00:17:41
    junction temperature this is the output
  • 00:17:43
    of the junction obviously I'm starting
  • 00:17:44
    from a low temperature 25 doesn't show
  • 00:17:47
    exactly what this is 25 and then we go
  • 00:17:50
    up
  • 00:17:51
    and here I'm already at a steady state
  • 00:17:56
    here I'm showing the drain current it's
  • 00:18:01
    about six a little bit actually lower
  • 00:18:03
    than that would fit in a minute
  • 00:18:06
    and then I have here the gate to Source
  • 00:18:09
    voltage with threshold voltage and here
  • 00:18:12
    I have it in expanded scale in this
  • 00:18:15
    region here I see that the temperature
  • 00:18:18
    went up to about I don't know 170 we'll
  • 00:18:22
    see it later on and then the currents
  • 00:18:25
    are about 6 amp and this is the gate to
  • 00:18:28
    Source voltage we see here some Peak
  • 00:18:33
    here due to probably capacitances and
  • 00:18:36
    and then we have this value here we'll
  • 00:18:40
    see it later on the exact value okay so
  • 00:18:43
    this is a typical run I don't have to
  • 00:18:45
    add any information all the thermal
  • 00:18:47
    information is within the model of the
  • 00:18:50
    transistor okay so here are some
  • 00:18:55
    other plots with some more information
  • 00:18:57
    for same run again Junction temperature
  • 00:19:01
    here it is now I've measured it to be
  • 00:19:04
    175 degrees Centigrade
  • 00:19:08
    here I'm showing the power
  • 00:19:11
    the power is measured by looking at the
  • 00:19:15
    current here because this current here
  • 00:19:18
    is this current which is coming from the
  • 00:19:22
    current search with represent the power
  • 00:19:25
    and its steady state of course the
  • 00:19:28
    current through the capacitor is zero so
  • 00:19:30
    we see here actually the power coming
  • 00:19:33
    from here to the output okay so that's
  • 00:19:36
    the current through
  • 00:19:38
    voltage source V4 and here it is this is
  • 00:19:43
    at this point here this region here it's
  • 00:19:46
    550. now the current now I've measured
  • 00:19:50
    it to be 5.5 amp the current here if
  • 00:19:54
    this is the current that passes through
  • 00:19:57
    I4 this is this current here so this is
  • 00:20:00
    5.5 now we can do a sort of a sanity
  • 00:20:04
    check here the voltage is 1000 volt the
  • 00:20:07
    current is 5.5
  • 00:20:10
    the duty cycle is 0.1 so the average
  • 00:20:14
    power is 550 Watts this is what I see
  • 00:20:18
    here 551 so everything seems to be
  • 00:20:22
    okay in terms of the inner parameters of
  • 00:20:27
    this model now I can check it against
  • 00:20:30
    this thermaline pins okay check it here
  • 00:20:35
    so I found it from the simulation that
  • 00:20:38
    the temperature should have gone up here
  • 00:20:40
    it is 175.
  • 00:20:43
    so we can get this number for this
  • 00:20:46
    particular case which is a simple case
  • 00:20:48
    because this is a train of pulses
  • 00:20:51
    which is compatible with this plot now
  • 00:20:55
    we have a 0.1 well I've covered it but
  • 00:21:00
    this is a duty cycle of 0.1 we have 10
  • 00:21:03
    microseconds so the thermal resistance
  • 00:21:07
    or thermal impedance is 0.03
  • 00:21:11
    okay or 30 Milli degree Centigrade per
  • 00:21:15
    watt now the power we already know is
  • 00:21:19
    5.51 kilowatt this is the peak power
  • 00:21:22
    which we are using here you are not
  • 00:21:24
    using here the average you are using
  • 00:21:26
    here the pick
  • 00:21:27
    so we have the peak power of 5.5
  • 00:21:30
    kilowatt and we multiply this 5.5
  • 00:21:34
    kilowatt by 30 this Milli degree
  • 00:21:39
    Centigrade per watt 0.03 and I'm getting
  • 00:21:44
    165 now you have to add to it 25 degrees
  • 00:21:49
    because this is just the junction to
  • 00:21:52
    case so I have to add the 25 degree I
  • 00:21:55
    will get the 190 in the simulation I got
  • 00:21:59
    175 well that's not that bad well could
  • 00:22:04
    have been better but it's pretty good
  • 00:22:06
    let's have a look now at this safe
  • 00:22:09
    operating area plot
  • 00:22:11
    and see where we are at as compared to
  • 00:22:15
    the model okay so I have a case here
  • 00:22:18
    which I marked here of 1000 volt
  • 00:22:24
    and I see that I'm getting to the Limit
  • 00:22:28
    here
  • 00:22:30
    with a current of 18 M okay this is 10
  • 00:22:34
    this will be 20. so it's about 18 amp
  • 00:22:39
    okay so I now can can simulate this case
  • 00:22:44
    with the model
  • 00:22:46
    and in this case here is the pulse okay
  • 00:22:50
    the single pulse
  • 00:22:52
    start from 25 degrees going up to uh
  • 00:22:56
    to 106.
  • 00:22:59
    this is a 10 microsecond pulse this is
  • 00:23:02
    the case that I'm looking at
  • 00:23:04
    and this is 106 while the maximum
  • 00:23:09
    Junction temperature
  • 00:23:11
    specified by the
  • 00:23:14
    manufacturer is 150
  • 00:23:17
    it's a long way it's a very long way
  • 00:23:20
    okay so I don't understand why the limit
  • 00:23:23
    here is 106 only
  • 00:23:26
    so just to see if maybe this is a wrong
  • 00:23:32
    point or whatever I've tried another
  • 00:23:35
    point in this case it's 100 volt okay so
  • 00:23:39
    I've adjusted the voltage so to be 100
  • 00:23:41
    volt and the current to be 50 amp
  • 00:23:46
    with a pulse width of 100 microsecond
  • 00:23:51
    and here is what I'm getting in this
  • 00:23:53
    case this is the temperature of the
  • 00:23:56
    pulse this is the current 50 amp and you
  • 00:24:00
    see that I'm getting again 109 so
  • 00:24:03
    obviously the limit
  • 00:24:07
    here is probably 100 volt this is a
  • 00:24:11
    little bit too low okay so it's sort of
  • 00:24:13
    underestimates it's a big big safety
  • 00:24:15
    factor and for a 150 degree device
  • 00:24:20
    setting the limit here to 100 it's a
  • 00:24:24
    little bit too much so this brings me to
  • 00:24:27
    the end of this presentation I hope you
  • 00:24:30
    found it of interest and perhaps it will
  • 00:24:32
    be useful to you in the future thank you
  • 00:24:35
    very much
タグ
  • silicon carbide
  • thermal impedance
  • safe operating area
  • junction temperature
  • transistor
  • simulation
  • thermal resistance
  • Multisim
  • thermal capacitance