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Semiconductor Devices
The Diode block represents one of the following types of diodes:
The piecewise linear diode model is the same model found in the Simscape Diode block, with the addition of a fixed junction capacitance. If the diode forward voltage exceeds the value specified in the Forward voltage parameter, the diode behaves as a linear resistor with the resistance specified in the On resistance parameter. Otherwise, the diode behaves as a linear resistor with the small conductance specified in the Off conductance parameter. Zero voltage across the diode results in zero current flowing.
The piecewise linear zener diode model behaves like the piecewise linear diode model for bias voltages above –Vz, where Vz is the Reverse breakdown voltage Vz parameter value. For voltages less than –Vz, the diode behaves as a linear resistor with the low Zener resistance specified in the Zener resistance Rz parameter. This diode model also includes a fixed junction capacitance.
Note The Reverse breakdown voltage Vz parameter is defined as a positive number. The p-n voltage at breakdown is –Vz, which is negative. |
The exponential diode model provides the following relationship between the diode current I and the diode voltage V:
where:
q is the elementary charge on an electron (1.602176e–19 Coulombs).
k is the Boltzmann constant (1.3806503e–23 J/K).
Vz is the Reverse breakdown voltage BV parameter value.
N is the emission coefficient.
IS is the saturation current.
T is the temperature at which the diode parameters are specified, as defined by the Measurement temperature parameter value.
When
, the block replaces
with
, which matches the gradient
of the diode current at
and extrapolates
linearly. When
, the block replaces
with
, which also matches the gradient
and extrapolates linearly. Typical electrical circuits do not reach
these extreme values. The block provides this linear extrapolation
to help convergence when solving for the constraints during simulation.
When you select Use parameters IS and N for the Parameterization parameter, you specify the diode in terms of the Saturation current IS and Emission coefficient N parameters. When you select Use I-V curve data points for the Parameterization parameter, you specify two voltage and current measurement points on the diode I-V curve and the block derives the IS and N values. When you specify current and voltage measurements, the block calculates IS and N as follows:
where:
.
V1 and V2 are the values in the Voltages [V1 V2] vector.
I1 and I2 are the values in the Currents [I1 I2] vector.
The exponential diode model provides the option to include a junction capacitance:
When you select Include fixed or zero junction capacitance for the Junction capacitance parameter, the capacitance is fixed.
When you select Use parameters CJO, VJ, M & FC for the Junction capacitance parameter, the block uses the coefficients CJO, VJ, M, and FC to calculate a junction capacitance that depends on the junction voltage.
When you select Use C-V curve data points for the Junction capacitance parameter, the block uses three capacitance values on the C-V capacitance curve to estimate CJO, VJ, and M and uses these values with the specified value of FC to calculate a junction capacitance that depends on the junction voltage. The block calculates CJO, VJ, and M as follows:
where:
VR1, VR2, and VR3 are the values in the Reverse bias voltages [VR1 VR2 VR3] vector.
C1, C2, and C3 are the values in the Corresponding capacitances [C1 C2 C3] vector.
It is not possible to estimate FC reliably from tabulated data, so you must specify its value using the Capacitance coefficient FC parameter. In the absence of suitable data for this parameter, use a typical value of 0.5.
The reverse bias voltages (defined as positive values) should satisfy VR3 > VR2 > VR1. This means that the capacitances should satisfy C1 > C2 > C3 as reverse bias widens the depletion region and hence reduces capacitance. Violating these inequalities results in an error. Voltages VR2 and VR3 should be well away from the Junction potential VJ. Voltage VR1 should be less than the Junction potential VJ, with a typical value for VR1 being 0.1 V.
The voltage-dependent junction is defined in terms of the capacitor charge storage Qj as:
For
:
For
:
where:
These equations are the same as used in [2], except that the temperature dependence of VJ and FC is not modeled. This model does not include the diffusion capacitance term that affects performance for high frequency switching applications.
The Exponential diode model has the following limitations:
When you select Use I-V curve data points for the Parameterization parameter, choose a pair of voltages near the diode turn-on voltage. Typically, this is in the range from 0.05 to 1 Volt. Using values outside of this region may lead to numerical issues and poor estimates for IS and N.
This block does not model temperature-dependent effects. SimElectronics® simulates the block at the temperature at which the component behavior was measured, as specified by the Measurement temperature parameter value.
You may need to use nonzero ohmic resistance and junction capacitance values to prevent numerical simulation issues, but the simulation may run faster with these values set to zero.
Select one of the following diode models:
Piecewise Linear (Foundation Library) — Use a piecewise linear model for the diode, as described in Piecewise Linear. This is the default method.
Piecewise Linear Zener — Use a piecewise linear model with reverse breakdown characteristics for the diode, as described in Piecewise Linear Zener.
Exponential — Use a standard exponential model for the diode, as described in Exponential.
Minimum voltage that needs to be applied for the diode to become forward-biased. This parameter is only visible when you select Piecewise Linear (Foundation Library) or Piecewise Linear Zener for the Diode model parameter. The default value is 0.6 V.
The resistance of the diode when it is forward biased. This parameter is only visible when you select Piecewise Linear (Foundation Library) or Piecewise Linear Zener for the Diode model parameter. The default value is 0.3 Ω.
The conductance of the diode when it is reverse biased. This parameter is only visible when you select Piecewise Linear (Foundation Library) or Piecewise Linear Zener for the Diode model parameter. The default value is 1e-08 1/Ω.
Select one of the following methods for model parameterization:
Use I-V curve data points — Specify measured data at two points on the diode I-V curve. This is the default method.
Use parameters IS and N — Specify saturation current and emission coefficient.
A vector of the current values at the two points on the diode I-V curve that the block uses to calculate IS and N. This parameter is only visible when you select Exponential for the Diode model parameter and Use I-V curve data points for the Parameterization parameter. The default value is [ 0.07 1.5 ] A.
A vector of the voltage values at the two points on the diode I-V curve that the block uses to calculate IS and N. This parameter is only visible when you select Exponential for the Diode model parameter and Use I-V curve data points for the Parameterization parameter. The default value is [ 0.7 0.8 ] V.
The magnitude of the current that the ideal diode equation approaches asymptotically for very large reverse bias levels. This parameter is only visible when you select Exponential for the Diode model parameter and Use parameters IS and N for the Parameterization parameter. The default value is 1e-14 A.
The temperature at which IS or the I-V curve was measured. This parameter is only visible when you select Exponential for the Diode model parameter. The default value is 25 °C.
The diode emission coefficient or ideality factor. This parameter is only visible when you select Exponential for the Diode model parameter and Use parameters IS and N for the Parameterization parameter. The default value is 1.
The resistance of the diode when the voltage is less than the Reverse breakdown voltage Vz value. This parameter is only visible when you select Piecewise Linear Zener for the Diode model parameter. The default value is 0.3 Ω.
The reverse voltage below which the diode resistance changes to the Zener resistance Rz value. This parameter is only visible when you select Piecewise Linear Zener for the Diode model parameter. The default value is 50 V.
The reverse voltage below which to model the rapid increase in conductance that occurs at diode breakdown. This parameter is only visible when you select Exponential for the Diode model parameter. The default value is Inf V, which effectively omits reverse breakdown from the model.
The series diode connection resistance. This parameter is only visible when you select Exponential for the Diode model parameter. The default value is 0.01 Ω.
When you select Piecewise Linear (Foundation Library) or Piecewise Linear Zener for the Diode model parameter, the Junction capacitance parameter is the fixed junction capacitance value. The default value is 5 pF.
When you select Exponential for the Diode model parameter, the Junction capacitance parameter lets you select one of the following options for modeling the junction capacitance:
Include fixed or zero junction capacitance — Model the junction capacitance as a fixed value.
Use C-V curve data points — Specify measured data at three points on the diode C-V curve.
Use parameters CJ0, VJ, M & FC — Specify zero-bias junction capacitance, junction potential, grading coefficient, and forward-bias depletion capacitance coefficient.
The value of the capacitance placed in parallel with the exponential diode term. This parameter is only visible when you select Exponential for the Diode model parameter and Include fixed or zero junction capacitance or Use parameters CJ0, VJ, M & FC for the Junction capacitance parameter. The default value is 5 pF.
A vector of the reverse bias voltage values at the three points on the diode C-V curve that the block uses to calculate CJ0, VJ, and M. This parameter is only visible when you select Use C-V curve data points for the Junction capacitance parameter. The default value is [ 0.1 10 100 ] V.
A vector of the capacitance values at the three points on the diode C-V curve that the block uses to calculate CJ0, VJ, and M. This parameter is only visible when you select Use C-V curve data points for the Junction capacitance parameter. The default value is [ 3.5 1 0.4 ] pF.
The junction potential. This parameter is only visible when you select Exponential for the Diode model parameter and Use parameters CJ0, VJ, M & FC for the Junction capacitance parameter. The default value is 1 V.
The grading coefficient. This parameter is only visible when you select Exponential for the Diode model parameter and Use parameters CJ0, VJ, M & FC for the Junction capacitance parameter. The default value is 0.5.
Fitting coefficient that quantifies the decrease of the depletion capacitance with applied voltage. This parameter is only visible when you select Exponential for the Diode model parameter and Use C-V curve data points or Use parameters CJ0, VJ, M & FC for the Junction capacitance parameter. The default value is 0.5.
The block has the following ports:
Electrical conserving port associated with the diode positive terminal.
Electrical conserving port associated with the diode negative terminal.
[1] MH. Ahmed and P.J. Spreadbury. Analogue and digital electronics for engineers. 2nd Edition, Cambridge University Press, 1984.
[2] G. Massobrio and P. Antognetti. Semiconductor Device Modeling with SPICE. 2nd Edition, McGraw-Hill, 1993.
Simscape Diode, Diode (SPICE)
 | DC Voltage Source | Diode (SPICE) |  |
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