# Diode

Piecewise linear diode

## Library

Semiconductors / Fundamental Components

## Description

The Diode block models a piecewise linear diode.

If the voltage across the diode exceeds the value specified in the block Forward voltage parameter, then the diode behaves like a linear resistor plus a series voltage source. The value of the On resistance parameter specifies the resistance of the linear resistor.

If the voltage across the diode is less than the forward voltage, the diode behaves like a linear resistor with low conductance specified by the value of the Off conductance parameter.

When forward biased, the series voltage source is given by

`$V=Vf\left(1-{R}_{on}{G}_{off}\right),$`

where:

• V is the voltage supplied by the series voltage source.

• Vf is the forward voltage.

• Ron is the on resistance.

• Goff is the off conductance.

The Ron*Goff term ensures that the diode current is exactly zero when the voltage across it is zero.

The figure shows a typical I-V characteristic for a diode device.

### Modeling Variants

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

• No thermal port — This variant does not simulate heat generation in the device. This variant is the default.

• Show thermal port — This variant contains a thermal port that allows you to model the heat that 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. When you select a thermal variant of the block, the thermal port appears.

## Ports

`+`

Electrical conserving port associated with the diode positive terminal

`-`

Electrical conserving port associated with the diode negative 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

Forward voltage

Minimum voltage required across the `+` and `-` block ports for the gradient of the diode I-V characteristic to be 1/Ron, where Ron is the value of On resistance. The default value is `0.8` `V`.

On resistance

Rate of change of voltage versus current above the Forward voltage. The default value is `0.001` `Ohm`.

Off conductance

Conductance of the reverse-biased diode. The default value is `1e-5` `1/Ohm`.

Number of series diodes

The number of diodes connected in series between the `+` and `-` block ports. Each diode has the Forward voltage, On resistance, and Off conductance that you specify. The default value is `1`.

Number of parallel diodes

The number of parallel diodes, or number of parallel paths formed by series-connected diodes, between the `+` and `-` block ports. Each diode has the Forward voltage, On resistance, and Off conductance that you specify. The default value is `1`.