MOSFET (Ideal, Switching)
Ideal N-channel MOSFET for switching applications
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Simscape / Electrical / Semiconductors & Converters
Description
The MOSFET (Ideal, Switching) block models the ideal switching behavior of an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET).
The switching characteristic of an n-channel MOSFET is such that if the gate-source voltage exceeds the specified threshold voltage, the MOSFET is in the on state. Otherwise, the device is in the off state. This figure shows a typical i-v characteristic:
To define the I-V characteristic of the MOSFET, set the On-state behaviour and
switching losses parameter to either Specify constant
values
or Tabulate with temperature and current
.
The Tabulate with temperature and current
option is available only
if you expose the thermal port of the block.
In the on state, the drain-source path behaves like a linear resistor with resistance, Rds_on. However, if you expose the thermal port of the block and parameterize the device using tabulated I-V data, the tabulated resistance is a function of the temperature and current.
In the off state, the drain-source path behaves like a linear resistor with low off-state conductance, Goff.
The defining Simscape™ equations for the block are:
if G > Vth v == i*Rds_on; else v == i/Goff; end
where:
G is the gate-source voltage.
Vth is the threshold voltage.
v is the drain-source voltage.
i is the drain-source current.
Rds_on is the on-state resistance.
Goff is the off-state conductance.
Using the Integral Diode settings, you can include the body diode or an integral protection diode. The integral diode provides a conduction path for reverse current. For example, to provide a path for a high reverse-voltage spike that is generated when a semiconductor device suddenly switches off the voltage supply to an inductive load.
Set the Integral protection diode parameter based on your goal.
Goal | Value to Select | Block Behavior |
---|---|---|
Prioritize simulation speed. | Protection diode with no dynamics | The block includes an integral copy of the Diode block. To parameterize the internal Diode block, use the Protection parameters. |
Precisely specify reverse-mode charge dynamics. | Protection diode with charge dynamics | The block includes an integral copy of the dynamic model of the Diode block. To parameterize the internal Diode block, use the Protection parameters. |
Model Gate Port and Thermal Effects
You can choose between physical or electrical ports to control the gate terminal and expose the thermal port to model the heat that switching events and conduction losses generate. To choose the gate control port and expose the thermal port, set the Modeling option parameter to either:
PS control port
— Contains a physical signal port that is associated with the gate terminal.Electrical control port
— Contains an electrical conserving port that is associated with the gate terminal.PS control port | Thermal port
— Contains a thermal port and a physical signal port that is associated with the gate terminal.Electrical control port | Thermal port
— Contains a thermal port and an electrical conserving port that is associated with the gate terminal.
For more information about using thermal ports, see Simulating Thermal Effects in Semiconductors.
Thermal Losses
The figure shows an idealized representation of the output voltage, Vout, and the output current, Iout, of the semiconductor device. The interval shown includes the entire nth switching cycle, during which the block turns off and then on.
Switching losses are one of the main sources of thermal loss in semiconductors. During each on-off switching transition, the MOSFET parasitics store and then dissipate energy.
Switching losses depend on the off-state voltage and the on-state current. When a switching device is turned on, the power losses depend on the initial off-state voltage across the device and the final on-state current once the device is fully in its on state. Similarly, when a switching device is turned off, the power losses depend on the initial on-state current through the device and the final off-state voltage across the device when in the fully off state.
In this block, switching losses are applied by stepping up the junction temperature with a value equal to the switching loss divided by the total thermal mass at the junction. The Switch-on loss, Eon(Tj,Ids) and Switch-on loss, Eoff(Tj,Ids) parameter values set the sizes of the switching losses and they are either fixed or dependent on junction temperature and drain-source current. In both cases, losses are scaled by the off-state voltage prior to the latest device turn-on event.
Note
As the final current after a switching event is not known during the simulation, the block records the on-state current at the point that the device is commanded off. Similarly, the block records the off-state voltage at the point that the device is commanded on. For this reason, the simlog does not report the switching losses to the thermal network until one switching cycle later.
For all ideal switching devices, the switching losses are reported in the simlog as
lastTurnOffLoss
and lastTurnOnLoss
and recorded as
a pulse with amplitude equal to the energy loss. If you use a script to sum the total
losses over a defined simulation period, you must sum the pulse values at each pulse
rising edge. Alternatively, you can use the ee_getPowerLossSummary
and ee_getPowerLossTimeSeries
functions to extract conduction and switching
losses from logged data.
Variables
The Variables settings allow you to specify the priority and initial target values for block variables before simulation. For more information, see Set Priority and Initial Target for Block Variables.
To enable the Variables settings for this block, set the
Modeling option parameter to PS control port | Thermal
port
or Electrical control port | Thermal
port
.
Ports
The figure shows the block port names.