Optocoupler
A dynamic model (or behavioural model) of an optocoupler consisting of an LED, a current sensor and a controlled current source.
Description
The Optocoupler unit is an optocoupler consisting of the following components:
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An exponential LED connected in series with a current sensor at the input;
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A controlled current source at the output.
The output current flows from the collector to the emitter. It is equal to , where is the current gain value and is the diode current.
Use an Optocoupler to interface two electrical circuits without direct galvanic coupling. For example, if the two circuits operate at different voltage levels.
| Each circuit must have its own Electrical Reference. |
If the optocoupler output is a phototransistor, the Current transfer ratio values are typically 0.1-0.5. If the optocoupler output is a Darlington pair (composite transistor), the Current transfer ratio value can be much higher than this. The Current transfer ratio may vary with LED current, but this effect is not modelled in the Photodiode block.
Some manufacturers specify a maximum transfer rate for optocouplers. In practice, the maximum data transfer rate depends on the following parameters:
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Photodiode capacitance and type of control circuit;
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The design of the phototransistor and its corresponding capacitance.
In the Optocoupler block it is possible to set the capacitance of the light emitting diode only. You can use the Junction capacitance parameter to set your own collector-to-emitter capacitance data.
The Optocoupler block allows you to model the temperature dependence of the base diode. For more information see Diode.
Thermal Port
You can enable the thermal port to model the mutual influence of the device’s heat dissipation and its temperature. To include or not include thermal elements, set the Modelling option to one of the following values:
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No thermal port- the block does not contain a thermal port and thermal effects in the device are not taken into account; -
Show thermal port- the block contains a thermal port, which allows modelling the heat generated by conduction losses. To improve the efficiency of calculations, the thermal state does not affect the electrical behaviour of the block.
Assumptions and limitations
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The circuit section at the output of the optocoupler is modelled as a controlled current source. Thus, it only faithfully approximates a bipolar transistor operating in its normal active region. To create a more detailed model, connect the optocoupler output directly to the base of the NPN bipolar transistor block and adjust the parameters to maintain the correct overall current gain. If you need to connect the optocouplers in series, use this approach to avoid the unacceptable topology of two current sources connected in series.
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The temperature dependence of the current gain is not modelled. Typically, the temperature dependence of this parameter is much smaller than the temperature dependence of the volt-ampere characteristic (VAC) of an optical diode.
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It may be necessary to use non-zero values for the ohmic resistance and junction capacitance to avoid problems with the numerical modelling, but the numerical calculation may be faster if these values are set to zero.
Ports
Non-directional
+ - positive
electricity
The electrical port associated with the positive terminal.
- is negative
electricity
An electrical port associated with the negative terminal.
C is the collector
electricity
The electrical port associated with the collector terminal of a transistor.
E is the emitter
electricity
The electrical port associated with the emitter terminal of a transistor.
H is a thermal port
heat
Thermal non-directional port.
Dependencies
To enable this port, select the checkbox for Enable thermal port.
Parameters
Main
Enable thermal port - enable thermal port
` disabled (by default)` | enabled
Modelling of thermal effects.
To enable thermal effects modelling, set the checkbox to enabled.
Current transfer ratio - current transfer ratio
0.2 (By default).
The output current flowing from the collector to the emitter of the transistor is equal to the product of the current transfer ratio and the LED current.
parameterization - model parameterization
Use I-V curve data points (by default) | Use parameters IS and N.
Select one of the following model parameterization methods:
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Use I-V curve data points- set the measured data at two points of the diode volt-ampere curve. -
Use parameters IS and N- set the saturation current (IS) and emission coefficient (N).
Currents [I1 I2] - vector of current values at two points
[0.001, 0.015] A (by default) | `vector 1 to 2'.
Vector of current values at two points of the diode volt-ampere characteristic curve, which the block uses to calculate the saturation current (IS) and emission coefficient (N).
Dependencies
To enable this parameter, set parameterization to `Use I-V curve data points'.
Data types:Float64
Voltages [V1 V2] - vector of voltage values at two points
[0.9, 1.05] V (by default) | vector 1 to 2
Vector of voltage values at two points of the diode volt-ampere characteristic curve, which the block uses to calculate the saturation current (IS) and emission coefficient (N).
Dependencies
To enable this parameter, set parameterization to `Use I-V curve data points'.
Data types:Float64
Ohmic resistance, RS - diode resistance
0.1 Ohm (By default) | scalar
Series ohmic resistance of the diode.
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Data types:*
Float64
Saturation current, IS - saturation current
1e-10 A (By default) | scalar
The magnitude of current to which the ideal diode equation approaches asymptotically for very large reverse bias levels.
Dependencies
To enable this parameter, set the Parameterization parameter to Use parameters IS and N.
Measurement temperature - measurement temperature
25 degC (by default) | scalar.
The temperature at which the saturation current curve (IS) or volt-ampere characteristic curve of the diode was measured. The value by default is `25 degC.
Data types:Float64
Emission coefficient, N - diode emission coefficient
2 (by default) | scalar
The emission coefficient of the diode, or ideality coefficient.
Dependencies
To enable this parameter, set parameterization to Use parameters IS and N.
Data types:Float64.
Junction Capacitance
Capacitance - diode junction capacitance modelling
Fixed or zero junction capacitance (by default) | Use C-V curve data points | Use parameters CJ0, VJ, M & FC
Select one of the following diode junction capacitance modelling options:
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Fixed or zero junction capacitance- modelling the junction capacitance as a fixed value; -
Use C-V curve data points- set the measured data at the three C-V curve points of the diode; -
Use parameters CJ0, VJ, M & FC- set the zero bias junction capacitance, the junction contact potential difference, the smoothness factor and the nonlinearity factor of the forward bias junction barrier capacitance.
Junction capacitance is the junction capacitance
5 pF (by default) | scalar
Fixed value of junction capacitance.
Dependencies
To enable this parameter, set Capacitance to `Fixed or zero junction capacitance'.
Data types:Float64.
Zero-bias junction capacitance, CJ0 - junction capacitance at zero bias
capacitance 5 pF (by default) | scalar
Value of capacitance connected in parallel to an exponential diode.
Dependencies
To enable this parameter, set Capacitance to Use parameters CJ0, VJ, M & FC.
Data types:Float64.
Junction potential, VJ - contact potential difference of transition
1 V (by default) | scalar
Contact potential difference of the transition.
Dependencies
To enable this parameter, set the Capacitance parameter to Use parameters CJ0, VJ, M & FC.
Data types:Float64.
Grading coefficient, M - coefficient that takes into account smoothness of transition
0.5 (by default) | scalar
A coefficient quantifying the smoothness of the p-n junction.
Dependencies
To enable this parameter, set Capacitance to Use parameters CJ0, VJ, M & FC.
Data types:Float64.
Reverse bias voltages [VR1 VR2 VR3] - vector of reverse bias voltages
[0.1, 10.0, 100.0] V (by default) | vector 1 to 3
A vector of reverse bias voltage values at three points on the diode’s C-V curve that the block uses to calculate CJ0, VJ, and M.
Dependencies
To enable this parameter, set the Capacitance parameter to C-V curve data points.
Data types:Float64
Corresponding capacitances [C1 C2 C3] - vector of capacitances corresponding to the vector of reverse bias voltages
[3.5, 1.0, 0.4] pF (by default) | vector 1 to 3
The vector of capacitance values at three points on the diode’s C-V curve that the block uses to calculate CJ0, VJ, and M.
Dependencies
To enable this parameter, set the Capacitance parameter to C-V curve data points.
Data types:Float64
Capacitance coefficient, FC - nonlinearity coefficient of the barrier capacitance of the forward biased transition
0.5 (by default) | scalar
A coefficient that quantifies the decrease in discharge capacitance with applied voltage.
Dependencies
To enable this parameter, set Capacitance to `C-V curve data points'.
Data types:Float64
Temperature Dependence
parameterization - parameterization of temperature dependence
None - Use characteristics at parameter measurement temperature (By default) | Use an I-V data point at second measurement temperature | Specify saturation current at second measurement temperature | Specify the energy gap, EG
Select one of the following methods for parameterising the temperature dependence:
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None - Use characteristics at parameter measurement temperature- the temperature dependence is not modelled, or the model is modelled at measurement temperature (as specified in Measurement temperature. This is the by default method). -
Use an I-V data point at second measurement temperature- when selected, this value specifies the second measurement temperature and the current and voltage values at that temperature. The model uses these values along with the parameter values at the first measurement temperature to calculate the bandgap value. -
Specify saturation current at second measurement temperature- selecting this value specifies the second measurement temperature and the saturation current value at that temperature. The model uses these values together with the parameter values at the first measurement temperature to calculate the forbidden band width value. -
Specify the energy gap, EG- set the forbidden zone width value manually.
Current I1 at second measurement temperature - current I1 at second measurement temperature
0.029 A (By default) | scalar.
Specify the value of current I1 on the diode when the voltage is equal to V1 at the second measurement temperature.
Dependencies
To enable this parameter, set parameterization to `Use an I-V data point at second measurement temperature'.
Data types:Float64
Voltage V1 at second temperature measurement - voltage V1 at second temperature measurement
1.05 V (By default) | scalar
Specify the value of the voltage across diode V1 when the current is equal to I1 at the second measurement temperature.
Dependencies
To enable this parameter, set parameterization to `Use an I-V data point at second measurement temperature'.
Data types:Float64
Saturation current, IS, at second measurement temperature - saturation current, IS, at second measurement temperature
1.8e-8 A (by default) | scalar
Specify the value of saturation current, IS, at second measurement temperature.
Dependencies
To enable this parameter, set the Parameterization parameter to `Specify saturation current at second measurement temperature'.
Data types:Float64
Second measurement temperature - second measurement temperature
125 degC (by default) | scalar
Specify the value for the second measurement temperature.
Dependencies
To enable this parameter, set parameterization to `Use an I-V data point at second temperature measurement'.
Data types:Float64
Energy gap parameterization - parameterization of the forbidden zone width
Use nominal value for silicon (EG=1.11eV) (default) | Use nominal value for 4H-SiC silicon carbide (EG=3.23eV) | Use nominal value for 6H-SiC silicon carbide (EG=3.00eV) | Use nominal value for germanium (EG=0.67eV) | Use nominal value for gallium arsenide (EG=1.43eV) | Use nominal value for selenium (EG=1.74eV) | Use nominal value for Schottky barrier diodes (EG=0.69eV) | Specify a custom value
Select a value for the forbidden zone width from the list of preset parameters or specify a custom value:
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Use nominal value for silicon (EG=1.11eV)- the value by default; -
`Use nominal value for 4H-SiC silicon carbide (EG=3.23eV);
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Use nominal value for 6H-SiC silicon carbide (EG=3.00eV); -
Use nominal value for germanium (EG=0.67eV); -
`Use nominal value for gallium arsenide (EG=1.43eV);
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`Use nominal value for selenium (EG=1.74eV);
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Use nominal value for Schottky barrier diodes (EG=0.69eV); -
Specify a custom value- if you select this value, the Energy gap, EG parameter will appear in the dialogue box, allowing you to specify a custom value forEG.
Dependencies
To enable this parameter, set the Parameterization parameter to Specify the energy gap, EG.
Energy gap, EG is the width of the forbidden zone
1.11 eV (by default) | scalar.
Specify a custom value for the energy gap.
Dependencies
To enable this parameter, set the Energy gap parameterization parameter to Specify a custom value.
Saturation current temperature exponent parameterization - Saturation current temperature exponent parameterization
Use nominal value for pn-junction diode (XTI=3) (default) | Use nominal value for Schottky barrier diode (XTI=2) | Specify a custom value.
Select one of the following parameters to set the saturation current temperature value:
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Use nominal value for pn-junction diode (XTI=3)is the value used by default; -
Use nominal value for Schottky barrier diode (XTI=2); -
Specify a custom value- if you select this value, the dialogue box will show the parameter Saturation current temperature exponent, XTI - saturation current temperature exponent, allowing you to set a custom value forXTI.
Saturation current temperature exponent, XTI - saturation current temperature exponent
3 (By default) | scalar.
Specify a custom value for the saturation current temperature exponent, XTI.
Dependencies
To enable this parameter, set the Saturation current temperature exponent parameterization parameter to Specify a custom value.
Data types:Float64
Device simulation temperature - device temperature
25 degC (by default) | scalar
Specify the temperature value at which the device operation will be simulated.
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Data types:*
Float64
Initial Targets
Diode current
Priority - diode current priority
None (by default) | `High | Low
Diode current priority.
Value - diode current value
0.0 A (By default) | scalar
Diode current value.
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Data types:*
Float64