Fuse

Fuse that protects against excessive current

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  • Library:

  • Simscape / Electrical / Switches & Breakers

  • Fuse block

Description

The Fuse block breaks the circuit, to protect it against excessive current. The block provides the following modeling options:

  • Opening time is independent of current — The fuse opens when the current through the fuse exceeds the threshold current continuously for longer than the specified amount of time. This option assumes that the time to open is independent of the current. It also implicitly assumes that heat in the fuse is instantaneously dissipated once the current drops below a certain threshold.

  • Opening time depends on I^2*t — Makes fuse opening dependent on the energy dissipated in the fuse. The nominal melting value (I^2*t) is usually available on manufacturer datasheets. If you select this option, the fuse blows when:

    ∫toverti2dt≥I2t

    where tover is the time when the current crosses over the threshold current, i is instantaneous current through the fuse, and I2t is the nominal melting value from the datasheet. Use this option for high-current range of operation.

  • Opening time is tabulated — Makes fuse opening dependent on the average time-current tabulated data. This data indicates the time that it takes for the fuse to open given a certain current, and is available on manufacturer datasheets as time-current curves.

    For example, these are the time-current curves from a Littelfuse® 218 Series fuse datasheet.

    Select the appropriate curve and enter the corresponding current and time values into the Tabulated currents and Tabulated opening time parameter vectors, respectively. Use this option for small currents.

Ports

Conserving

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Electrical conserving port associated with the fuse positive terminal.

Electrical conserving port associated with the fuse negative terminal.

Output

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Outputs the fuse state as a unitless physical signal. The port outputs 0 if the fuse is intact, and 1 if the fuse is blown.

Dependencies

Exposed when the PS output for fuse state parameter is set to Visible.

Parameters

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Select whether opening time depends on current:

  • Opening time is independent of current — The fuse opens when the current through the fuse exceeds the threshold current continuously for longer than the specified amount of time.

  • Opening time depends on I^2*t — Makes fuse opening dependent on the energy dissipated in the fuse. Use this option for high-current range of operation.

  • Opening time is tabulated — Makes fuse opening dependent on the average time-current tabulated data. Use this option for small currents.

The fuse rating from the datasheet, or nominal operating current.

Dependencies

Enabled when the Parameterization parameter is set to Opening time is independent of current or Opening time depends on I^2*t.

Minimum melting current defines the fuse operating threshold. If the current through the fuse does not exceed this threshold, the fuse stays in low-ohmic state. With the default parameter value, 1, the threshold current is the same as the rated current. In most cases, this parameter value should be greater than 1. You can also set it to a value less than 1, for situations where the fuse may blow at a current level below the rated current (for example, due to high temperature, or due to repetitive pulses). The parameter value must be greater than 0.

Dependencies

Enabled when the Parameterization parameter is set to Opening time is independent of current or Opening time depends on I^2*t.

The amount of time needed for the fuse to blow. If the current through the fuse exceeds the threshold current continuously for longer than this amount of time, the fuse enters the high-ohmic state and breaks the circuit. If the current falls below the threshold before the time elapsed, the fuse stays in the low-ohmic state. If the current exceeds the threshold again, the time counter restarts. With the default parameter value, 0, the fuse blows immediately as soon as the current exceeds the minimum melting current. The parameter value must be greater than or equal to 0.

Dependencies

Enabled when the Parameterization parameter is set to Opening time is independent of current.

The amount of energy dissipated in the fuse that is needed for the fuse to blow. This is the nominal melting, or I2t, parameter from the datasheet. The value must be greater than or equal to 0.

Dependencies

Enabled when the Parameterization parameter is set to Opening time depends on I^2*t.

The tabulated current values from a time-current curve on the manufacturer datasheet. Every element in this vector must be greater than 0, and the vector must be strictly ascending.

Dependencies

Enabled when the Parameterization parameter is set to Opening time is tabulated.

The tabulated time values from a time-current curve on the manufacturer datasheet. Every element in this vector must be greater than or equal to 0, and the vector must be strictly descending. The vector must be of the same size as the Tabulated currents vector.

Dependencies

Enabled when the Parameterization parameter is set to Opening time is tabulated.

The fuse resistance in low-ohmic state. The parameter value must be greater than 0.

The open-circuit fuse conductance in high-ohmic state, when the fuse has blown. The parameter value must be greater than 0.

When set to Visible, a PS output port x appears on the block icon. The port outputs 0 if the fuse is intact, and 1 if the fuse is blown.

Model Examples

Automotive Electrical System

Automotive Electrical System

A simplified dynamic model of an automotive electrical system. The model contains electrical, mechanical, and thermal systems, and is able to simulate the effect of engine starting on the electrical network.

MOSFET Fault in Buck Converter

MOSFET Fault in Buck Converter

How a fault may be applied to a MOSFET in a power converter in order to explore the operation of protection circuitry. After the MOSFET becomes faulted, the crowbar circuitry is activated in order to clamp the output voltage across the load and eventually to cause the fuse to blow.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

See Also

Introduced in R2008b

Simscape Electrical Documentation

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