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MOSFET

N-channel MOSFET

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Semiconductors / Fundamental Components

Description

The MOSFET block models an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET).

The I-V 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.

In the on state, the drain-source path behaves like a linear resistor with resistance, Rds_on.

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 tab of the block dialog box, you can include an integral source-drain diode. An integral diode protects the semiconductor device by providing a conduction path for reverse current. An inductive load can produce a high reverse-voltage spike when the semiconductor device suddenly switches off the voltage supply to the load.

Set the Integral protection diode parameter based on your goal.

GoalValue to SelectBlock Behavior
Prioritize simulation speed.Protection diode with no dynamicsThe block includes an integral copy of the Diode block. The block dialog box shows parameters relating to the Diode block.
Precisely specify reverse-mode charge dynamics.Protection diode with charge dynamicsThe block includes an integral copy of the Commutation Diode block. The block dialog box shows parameters relating to the Commutation Diode block.

Modeling Variants

The block provides four modeling variants. To select the desired variant, right-click the block in your model. From the context menu, select Simscape > Block choices, and then one of these variants:

  • PS Control Port — Contains a physical signal port that is associated with the gate terminal. This variant is the default.

  • 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.

The variants of this block without the thermal port do not simulate heat generation in the device.

The variants with the thermal port allow you to model the heat that switching events and conduction losses generate. For numerical efficiency, the thermal state does not affect the electrical behavior of the block. The thermal port is hidden by default. To enable the thermal port, select a thermal block variant.

Thermal Loss Equations

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.

Heat Loss Due to a Switch-On Event

When the semiconductor turns on during the nth switching cycle, the amount of thermal energy that the device dissipates increments by a discrete amount. If you select Voltage, current, and temperature for the Thermal loss dependent on parameter, the equation for the incremental change is

Eon(n)=Voff(n)Voff_datafcn(T,Ion(n1)),

where:

  • Eon(n) is the switch-on loss at the nth switch-on event.

  • Voff(n) is the off-state output voltage,Vout, just before the device switches on during the nth switching cycle.

  • Voff_data is the Off-state voltage for losses data parameter value.

  • T is the device temperature.

  • Ion(n-1) is the on-state output current, Iout, just before the device switches off during the cycle that precedes the nth switching cycle.

The function fcn is a 2-D lookup table with linear interpolation and linear extrapolation:

E=tablelookup(Tj_data,Iout_data,Eon_data,T,Ion(n1)),

where:

  • Tj_data is the Temperature vector, Tj parameter value.

  • Iout_data is the Output current vector, Iout parameter value.

  • Eon_data is the Switch-on loss, Eon=fcn(Tj,Iout) parameter value.

If you select Voltage and current for the Thermal loss dependent on parameter, when the semiconductor turns on during the nth switching cycle, the equation that the block uses to calculate the incremental change in the discrete amount of thermal energy that the device dissipates is

Eon(n)=(Voff(n)Voff_data)(Ion(n1)Iout_scalar)(Eon_scalar)

where:

  • Iout_scalar is the Output current, Iout parameter value.

  • Eon_scalar is the Switch-on loss parameter value.

Heat Loss Due to a Switch-Off Event

When the semiconductor turns off during the nth switching cycle, the amount of thermal energy that the device dissipates increments by a discrete amount. If you select Voltage, current, and temperature for the Thermal loss dependent on parameter, the equation for the incremental change is

Eoff(n)=Voff(n)Voff_datafcn(T,Ion(n)),

where:

  • Eoff(n) is the switch-off loss at the nth switch-off event.

  • Voff(n) is the off-state output voltage, Vout, just before the device switches on during the nth switching cycle.

  • Voff_data is the Off-state voltage for losses data parameter value.

  • T is the device temperature.

  • Ion(n) is the on-state output current, Iout, just before the device switches off during the nth switching cycle.

The function fcn is a 2-D lookup table with linear interpolation and linear extrapolation:

E=tablelookup(Tj_data,Iout_data,Eoff_data,T,Ion(n)),

where:

  • Tj_data is the Temperature vector, Tj parameter value.

  • Iout_data is the Output current vector, Iout parameter value.

  • Eoff_data is the Switch-off loss, Eoff=fcn(Tj,Iout) parameter value.

If you select Voltage and current for the Thermal loss dependent on parameter, when the semiconductor turns off during the nth switching cycle, the equation that the block uses to calculate the incremental change in the discrete amount of thermal energy that the device dissipates is

Eoff(n)=(Voff(n)Voff_data)(Ion(n1)Iout_scalar)(Eoff_scalar)

where:

  • Iout_scalar is the Output current, Iout parameter value.

  • Eoff_scalar is the Switch-off loss parameter value.

Heat Loss Due to Electrical Conduction

If you select Voltage, current, and temperature for the Thermal loss dependent on parameter, then, for both the on state and the off state, the heat loss due to electrical conduction is

Econduction=fcn(T,Iout)dt,

where:

  • Econduction is the heat loss due to electrical conduction.

  • T is the device temperature.

  • Iout is the device output current.

The function fcn is a 2-D lookup table:

Qconduction=tablelookup(Tj_data,Iout_data,Iout_data_repmat.*Von_data,T,Iout),

where:

  • Tj_data is the Temperature vector, Tj parameter value.

  • Iout_data is the Output current vector, Iout parameter value.

  • Iout_data_repmat is a matrix that contains length, Tj_data, copies of Iout_data.

  • Von_data is the On-state voltage, Von=fcn(Tj,Iout) parameter value.

If you select Voltage and current for the Thermal loss dependent on parameter, then, for both the on state and the off state, the heat loss due to electrical conduction is

Econduction=(Iout*Von_scalar)dt,

where Von_scalar is the On-state voltage parameter value.

Heat Flow

The block uses the Energy dissipation time constant parameter to filter the amount of heat flow that the block outputs. The filtering allows the block to:

  • Avoid discrete increments for the heat flow output

  • Handle a variable switching frequency

The filtered heat flow is

Q=1τ(i=1nEon(i)+i=1nEoff(i)+EconductionQdt),

where:

  • Q is the heat flow from the component.

  • τ is the Energy dissipation time constant parameter value.

  • n is the number of switching cycles.

  • Eon(i) is the switch-on loss at the ith switch-on event.

  • Eoff(i) is the switch-off loss at the ith switch-off event.

  • Econduction is the heat loss due to electrical conduction.

  • ∫Qdt is the total heat previously dissipated from the component.

Ports

The figure shows the block port names.

G

Port associated with the gate terminal. You can set the port to either a physical signal or electrical port.

S

Electrical conserving port associated with the source terminal.

D

Electrical conserving port associated with the drain terminal.

H

Thermal conserving port. The thermal port is optional and is hidden by default. To enable this port, select a variant that includes a thermal port.

Parameters

Main Tab

On-state resistance, R_DS(on)

Drain-source resistance when the device is on. The default value is 0.01 Ohm.

Off-state conductance

Drain-source conductance when the device is off. The value must be less than 1/R, where R is the value of On-state resistance. The default value is 1e-6 1/Ohm.

Threshold voltage, Vth

Gate-source voltage threshold. The device turns on when the gate-source voltage is above this value. The default value is 2 V.

Integral Diode Tab

Integral protection diode

Block integral protection diode. The default value is Protection diode with no dynamics.

The diodes you can select are:

  • Protection diode with no dynamics

  • Protection diode with charge dynamics

Parameters for Protection diode with no dynamics

When you select Protection diode with no dynamics, additional parameters appear.

 Additional Parameters for Protection diode with no dynamics

Parameters for Protection diode with charge dynamics

When you select Protection diode with charge dynamics, additional parameters appear.

 Additional Parameters for Protection diode with charge dynamics

Thermal Model Tab

The Thermal Model tab is enabled only when you select a block variant that includes a thermal port.

Thermal loss dependent on

Select a parameterization method. The option that you select determines which other parameters are enabled. Options are:

  • Voltage and current — Use scalar values to specify the output current, switch-on loss, switch-off loss, and on-state voltage data.

  • Voltage, current, and temperature — Use vectors to specify the output current, switch-on loss, switch-off loss, on-state voltage, and temperature data. This is the default parameterization method.

Off-state voltage for losses data

The output voltage of the device during the off state. This is the blocking voltage at which the switch-on loss and switch-off loss data are defined. The default value is 300 V.

Energy dissipation time constant

Time constant used to average the switch-on losses, switch-off losses, and conduction losses. This value is equal to the period of the minimum switching frequency. The default value is 1e-4 s.

 Additional Parameters for Parameterizing by Voltage, Current, and Temperature

 Additional Parameters for Parameterizing by Voltage and Current

Introduced in R2013b

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