5.1. Power switches: discretes & modules

Contents

• Power switches: discretes & modules

  • Switches

  • Modules types

    • Discretes & leg modules

    • NPC modules

    • T-type modules

  • Switch and loss data

    • Conduction loss data

    • Switching loss data

  • Create a private power switch library element

    • Fill general information fields

    • Fill switch details fields

    • Fill conduction and switching losses fields

      • XML Files

      • Equations

PowerForge’s libraries cover different families of packaged switches, or modules.

Inside each module are one or several switches arranged in one of several configurations.

5.1.1. Switches

Power switches in PowerForge are the unit elements used to build the “elementary legs” of power conversion topologies.

Physically, a switch is the co-packaged anti-parallel connection of a transistor chip and/or a diode chip. Thermally, each of the two chips (if present) has its own junction-to-case thermal resistance specified by the manufacturer (which implies no thermal coupling internal to the package is taken into account).

In practice (especially in high-power modules) each one of these two may actually be several paralleled identical chips, but this is only of relevance to the module manufacturer: as in datasheets, PowerForge simply treats them as a larger equivalent chip (i.e. perfect internal current splitting and thermal balance are assumed).

Switches supported by PowerForge include:

• IGBT + anti-parallel diode

• Si/SiC MOSFET

• Si/SiC MOSFET + anti-parallel diode

• GaN FET

• stand-alone diode (no transistor)

Most of the topologies require switches able to carry current in both directions. In the conventional drawing orientation, the forward direction is top-to-bottom and the reverse direction is bottom-to-top.

All switches offer a spontaneous conduction mechanism (i.e. independent of the gate’s driving state) in the reverse direction. In the absence of a dedicated diode chip, this is due to an intrinsic property of the transistor chip’s technology (e.g. the source-to-drain ‘body diode’ in a power MOSFET).

Of course, switches with a transistor chip also offer a controlled conduction mechanism in the forward direction. Depending on the transistor technology, this controlled conduction mechanism may also be able to conduct current in the reverse direction (i.e. synchronous rectification).

Note

The harmonized description used in PowerForge means that a stand-alone diode is a switch that only conducts in the reverse direction.

5.1.2. Modules types

5.1.2.1. Discretes & leg modules

This library includes individually-packaged switches (often called discretes or single-switch modules) as well as modules containing 1 or several (often 3) pairs of identical switches arranged as phase legs (sometimes called dual-pack or 2-pack, 4-pack and 6-pack modules).

These are the most common module type, as they provide the basic building block for most power conversion topologies.

Note that such modules are homogeneous i.e. all the switches inside the package have identical characteristics: in essence, there are simply several instances of the same switch.

5.1.2.2. NPC modules

This library contains modules specifically designed for use in Neutral-Point Clamped converters. Their elementary pattern is a NPC leg with 2 outer switches, 2 inner switches and 2 clamp switches.

Note that the pattern is symmetric: both outer switches are necessarily similar, as are both inner switches and both clamp switches. Due to the NPC topology, the voltage rating of all switches is usually equivalent with the NPC leg rated at twice this.

In addition, because they don’t have to be actively controlled in a NPC converter, clamp switches are always stand-alone diodes (no transistors).

5.1.2.3. T-type modules

This library contains modules specifically designed for use in T-type neutral-point clamped converters. Their elementary pattern is a T-type leg with 2 outer switches and 2 anti-series inner switches.

Once again, both outer switches are similar, as are both inner switches. Due to the T-type topology, outer switches are rated at the full T-type leg voltage rating while inner switches usually are rated at half this voltage.

5.1.3. Switch and loss data

All data for each public reference found in PowerForge’s libraries has been extracted straight from its manufacturer datasheet using a proprietary internal process.

It is also possible to add private references. The user has the responsibility to input all ratings, thermal characteristics and other basic data with no check performed on them. See more information in this section

5.1.3.1. Conduction loss data

Voltage drops for computing conduction loss are obtained, in decreasing order of preference:

1. from \(R_{DS(on)} = f(T_j)\) curves (MOSFET only)

2. from I-V curves at different \(T_j\)

3. from a single I-V curve, assuming no temperature dependency

These curves are always taken at nominal gate drive voltage.

This results in one \(V_{drop} = f(I, T_j)\) lookup table for each of the spontaneous and controlled mechanisms, if present.

In addition, MOSFETs (with or without external diode) are capable of synchronous rectification: the controlled conduction mechanism (i.e. channel) can carry current in the reverse direction as well as the spontaneous conduction mechanism (i.e. body diode or external diode) with the share of total current flowing through each depending on each conduction characteristic curve (normally the MOSFET channel carries most of current, with the diode starting to take over at higher currents). Because solving for this current split ratio is costly compute-time-wise, PowerForge pre-computes it as a lookup table \(ratio = f(I_{reverse}, T_{j(channel)}, T_{j(diode)})\). See more information in Conduction loss.

5.1.3.2. Switching loss data

Transistor turn-off, turn-on and diode reverse-recovery energies are obtained, in decreasing order of preference:

1. from \(E_{off|on|rr} = f(I)\) curves at different \(T_j\) (this accounts for 2nd order effects)

2. from separate \(E_{off|on|rr} = f(I)\) and \(E_{off|on|rr} = f(T_j)\) curves

3. from a single \(E_{off|on|rr} = f(I)\) curve, assuming no temperature dependency

4. by a double-pulse measurement SPICE simulation based on transistor transfer curve, parasitic resistances and capacitances, diode reverse-recovery characteristics and an estimate of the package inductances (this is typically used only for low-voltage MOSFETs where manufacturers don’t provide double-pulse switching loss measurement results in datasheets)

Switching energies are always taken at nominal gate drive voltages and “default” external gate resistances (i.e. used by manufacturer in datasheet switching measurements).

Note that discrete IGBTs often have no reverse-recovery data provided by the manufacturer, in which case PowerForge will simply assume \(Err = 0\).

This results in three lookup tables \(E_{off} = f(V_{DC}, I, T_j)\), \(E_{on} = f(V_{DC}, I, T_j)\) and \(E_{rr} = f(V_{DC}, I, T_j)\).

5.1.4. Create a private power switch library element

The process described below is the same for any power switch library (“Leg modules & discretes”, “NPC modules” and “T-type modules”).

To create a new power switch library element, the user needs to click on “Create a private reference” on the main page.

Then, the user needs to fill the required fields and upload the data in the chosen format.

• Fill general information fields

• Fill switch details fields

• Fill conduction and switching losses fields

5.1.4.1. Fill general information fields

The following fields can be filled. Some of them are mandatory.

The explanation of each field can be found below:

Field	Necessity	Description
Reference	Mandatory	New name in the library.
Manufacturer	Mandatory	Manufacturer of the new reference. If the Manufacturer does not exist in the list of choices, a new Manufacturer can be specified by creating a new private reference in the Manufactures Library. If (Generic) is used, this object ill not have a manufacturer specified.
Technology	Mandatory	Must be selected from the following list: Si IGBT / Si MOSFET / SiC MOSFET / GaN FET.
Package	Mandatory	Package of the new reference. If the Package does not exist in the list of choices, a new Package can be specified by creating a new private reference in the Packages Library.
Qualification	Optional	Indicates if the reference is qualified according to the AEC-Q101 standard.
Availability status	Optional	Indicates the production status of the reference.
Normally On/Off	Optional	Indicates the default state of the switch.
RoHS	Optional	Indicates if the reference is qualified according to the RoHS standard.
Number of switches	Optional	Distinguishes between discrete and modules component.
Cost	Optional	Indicates the cost of the component based on the configured currency. This field can be modified at any time.
Comment	Optional	Custom comment. This field can be modified at any time.

5.1.4.2. Fill switch details fields

The following fields can be filled. Some of them are mandatory.

The explanation of each field can be found below:

Field	Necessity	Description
Vrated [V]	Mandatory	Maximum blocking voltage. Designs with Vpk > Vrated will be automatically unfeasible.
irated [A]	Mandatory	Maximum continuous current (usually @Tj =25°C).
Default RG(on) [Ω]	Mandatory	Gate resistance used at the turn-on / turn-off by default. Even though the losses do not depend on the gate resistance, it’s still mandatory to fill in this field. It will be used for informational purposes only. It is usually the manufacturer’s recommended value.
Default RG(off) [Ω]	Mandatory
VG(on) [V]	Case-dependent	Gate bias voltage used at “on” state / “off” state by default. If the losses depend on the gate bias voltage, it is mandatory to fill in this field. It is usually the manufacturer’s recommended value.
VG(off) [V]	Case-dependent
TjOp(max) [°C]	Mandatory	Maximum operating junction temperature for this component. Designs with Tj > TjOp(max) will be automatically unfeasible.
Transistor Rth(j-c) [°C/W]	Mandatory	Junction-to-case thermal resistance for the transistor chip.
Diode Rth(j-c) [°C/W]	Case-dependent	Junction-to-case thermal resistance for the diode chip. This field could be left empty if transistor and diode are not separated (e.g. body diode of a MOSFET).

Please, note that if some parameters are needed and not given for losses computation (e.g. R_G(on)|(off)), a warning message like below will appear:

5.1.4.3. Fill conduction and switching losses fields

Conduction and switching losses data can be provided from 3 main different ways:

• XML files: Commonly called “thermal datasheets”:

  • “XML thermal datasheets where both transistor and diode files are needed”. Select this option if the switch losses data are given in two separate files; often the case for IGBT or MOSFET with external diode.

  • “XML thermal datasheets where only one file is needed”. Select this option if the switch losses data are given in a single file; often the case for MOSFET or HEMT with body diode behaviour or IGBT with both transistor and diode data are provided.

• “Equations”:

  • This allows the user to provide losses data based on equations for any kind of technology. This option is only available for “Leg modules & Discretes” references.

5.1.4.3.1. XML Files

Most of the files provided by the following manufacturers can be interpreted (from February 2024):

• DYNEX

• GaN Systems

• GeneSiC

• Hitachi - ABB

• Infineon

• Microchip

• Qorvo

• ROHM

• Wolfspeed

• Semikron-Danfoss

• Cambridge GaN Devices

• onsemi

• EPC

5.1.4.3.2. Equations

The equation-based system allows to add component conduction and switching data.

Coefficients of polynomial equations are specified, for a specific junction temperature:

• Switching losses:

  • Switching energies at turn-on, turn-off and recovery depend on switched current and voltage:

  • \(E_{x}=(a_{0} + a_{1}\cdot I + a_{2}\cdot I^{2} + \dotsi + a_{n}\cdot I^{n})\cdot (β\cdot U^{α} + b_{0} + b_{1}\cdot U + b_{2}\cdot U^{2} + \dotsi + b_{m}\cdot U^{m})\)

• Conduction losses:

  • Conduction losses depend on threshold voltage \(V_{0}\), conduction resistance \(R_{D}\) and current \(I\):

  • \(V_{Drop}=V_{0} + R_{D}\cdot I + a_{2}\cdot I^{2} + \dotsi + a_{n}\cdot I^{n}\)

An example can be downloaded to illustrate the reference creation process (no temperature dependency, and switching energy is considered proportional to switched voltage).:

In this example, there isn’t any temperature dependency on both switching and conduction losses.

Linear interpolation/extrapolation will be processed for values not included in the samples.

Results of this example are illustrated below: