Diode Zener

Symbol

../../../_images/DiodeZener.svg

Information

../../../_images/DiodeZener.png

A Zener diode is a special type of diode that allows current to flow in the forward direction like a standard diode but also permits current in the reverse direction when the voltage exceeds a certain breakdown voltage.

The current-voltage relationship of a Zener diode follows the Shockley diode equation in forward bias and allows controlled conduction in reverse bias once breakdown voltage is reached.

Ports

  • p: Anode (positive terminal)

  • n: Cathode (negative terminal)

Model

The Zener Diode model represents both forward conduction and reverse breakdown behavior.

The Zener diode operates as a standard diode in forward bias and allows controlled reverse conduction once breakdown voltage is exceeded.

Attributes:

  • V (signal): Input voltage signal across the diode, defined between nodes (p, n).

  • I (signal): Output current signal through the diode, defined between nodes (p, n).

  • Iss (param): Saturation current (default: 1.0e-12 A), representing small leakage current.

  • Vt (param): Thermal voltage (default: 0.025 V), temperature-dependent.

  • N (param): Forward emission coefficient (default: 1.0), affecting diode equation.

  • BV (param): Breakdown voltage (default: 10.0 V), defining reverse conduction onset.

  • IBV (param): Breakdown current (default: 0.001 A), current at breakdown voltage.

Methods:

analog(): Defines the Zener diode behavior using:

\[I = I_{ss} (e^{V/V_t} - 1) + I_{BV} (e^{-(V + BV) / V_t} - 1) * (-1)\]
from pyams.lib import model, signal, param, voltage, current, explim

class DiodeZener(model):
    """
    Zener diode model with forward and reverse breakdown behavior.
    """

    def __init__(self, p, n):
        # Signal declaration
        self.V = signal('in', voltage, p, n)
        self.I = signal('out', current, p, n)

        # Parameter declaration
        self.Iss = param(1.0e-12, 'A', 'Saturation current')
        self.Vt = param(0.025, ' ', 'Thermal voltage')
        self.N = param(1.0, ' ', 'Forward emission coefficient')
        self.BV = param(10.0, 'V', 'Breakdown voltage')
        self.IBV = param(0.001, 'A', 'Breakdown current')

    def analog(self):
        """Defines the Zener diode’s voltage-current relationship."""
        Id = self.Iss * (explim(self.V / self.Vt) - 1)
        Ii = self.IBV * (explim(-(self.V + self.BV) / self.Vt) - 1) * -1
        self.I += Id + Ii

Command syntax

The syntax for defining a Zener diode in a PyAMS simulation:

# Import the model
from pyams.models import DiodeZener

# Dname: is the name of the Zener diode instance
# p, n: The connection points in the circuit
Dname = DiodeZener(p, n)