Diode

Piecewise linear diode in electrical systems

Libraries:
Simscape / Foundation Library / Electrical / Electrical Elements

Description

The Diode block models a piecewise linear diode. If the voltage across the diode is bigger than the Forward voltage parameter value, then the diode behaves like a linear resistor with low resistance, given by the On resistance parameter value, plus a constant series voltage source. If the voltage across the diode is less than the forward voltage, then the diode behaves like a linear resistor with low conductance given by the Off conductance parameter value.

Diode current plot

When forward biased, the diode behavior is described with the equations:

$\begin{array}{l} v = i \cdot R_{o n} + V_{s o u r c e}, \\ V_{s o u r c e} = V f (1 - R_{o n} G_{o f f}), \end{array}$

where:

v is the voltage.
i is the current.
V_source is the voltage of the series voltage source.
V_f is the forward voltage.
R_on is the resistance of the forward-biased diode.
G_off is the conductance of the reverse-biased diode.

The reverse behavior is given byv = i/G_off.

The R_on^.G_off term ensures that there is no discontinuity in the diode current when the diode is switching between the on and off states.

Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

Examples

Full-Wave Bridge Rectifier

An ideal AC transformer plus full-wave bridge rectifier. It converts 120 volts AC to 12 volts DC. The transformer has a turns ratio of 14, stepping the supply down to 8.6 volts rms, i.e. 8.6*sqrt(2) = 12 volts pk-pk. The full-wave bridge rectifier plus capacitor combination then converts this to DC. The resistor represents a typical load.

Open Model

Ports

Conserving

expand all

+ — Positive terminal
electrical

Electrical conserving port associated with the diode positive terminal.

- — Negative terminal
electrical

Electrical conserving port associated with the diode negative terminal.

Parameters

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Forward voltage — Minimum voltage for forward-biased diode
`0.6 V` (default) | positive scalar

Minimum voltage that needs to be applied for the diode to become forward biased.

On resistance — Resistance of forward-biased diode
`0.3 Ohm` (default) | positive scalar

The resistance of the forward-biased diode.

Off conductance — Conductance of reverse-biased diode
`1e-8 1/Ohm` (default) | positive scalar

The conductance of the reverse-biased diode.

Extended Capabilities

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

Version History

Introduced in R2007a

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R2023b: Reduced chattering near forward voltage

The block equations have been enhanced to reduce zero-crossings when the diode operates near the forward voltage.

In previous releases, the diode used

if v > Vf

as the switching condition between the on and off states. Starting with R2023b, the switching condition has been modified to include a resistance for zero-crossing detection, Rzc:

if v + i*Rzc < Vf + Vf*Goff*Rzc
    % Off
      i == v*Goff;
    else
    % On
       v == i*Ron + Vf*(1-Ron*Goff);

The new switching condition provides improved on-to-off and off-to-on characteristics when the diode operates near the forward voltage.

Diode

Description

Variables

Examples

Full-Wave Bridge Rectifier

Ports

Conserving

+ — Positive terminal electrical

- — Negative terminal electrical

Parameters

Forward voltage — Minimum voltage for forward-biased diode 0.6 V (default) | positive scalar

On resistance — Resistance of forward-biased diode 0.3 Ohm (default) | positive scalar

Off conductance — Conductance of reverse-biased diode 1e-8 1/Ohm (default) | positive scalar

Extended Capabilities

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

Version History

R2023b: Reduced chattering near forward voltage

See Also

+ — Positive terminal
electrical

- — Negative terminal
electrical

Forward voltage — Minimum voltage for forward-biased diode
`0.6 V` (default) | positive scalar

On resistance — Resistance of forward-biased diode
`0.3 Ohm` (default) | positive scalar

Off conductance — Conductance of reverse-biased diode
`1e-8 1/Ohm` (default) | positive scalar

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