Question
Explain the forward and the reverse characteristic of a Zener diode.
✓
Answer
The forward bias region of a Zener diode is identical to that of a regular diode. There is forward current only after the barrier potential of the pn- junction is overcome.
Beyond this threshold or cut in voltage, there is an exponential upward swing.
The typical forward voltage at room temperature with a current of around $1\ mA $is around $0.6\ V$ . In the reverse bias condition the Zener diode is an open circuit and only a small reverse saturation current flows as shown with change of scale.
At the reverse breakdown voltage there is an abrupt rapid increase in the current-the knee is very sharp, followed by an almost vertical increase in current.
The voltage across the Zener diode in the breakdown region is very nearly constant with only a small increase in voltage with increasing current.
There is a minimum Zener current, $I _{ Z }( min )$, that places the operating point in the desired breakdown region.
At some high current level, $I _{ ZM }$, the power dissipation of the diode becomes excessive beyond which the diode can be damaged.
Zener diode characteristics
The $I-V$ characteristics of a Zener diode is not totally vertical in the breakdown region. This means that for slight changes in current, there will be a small change in the voltage across the diode. The voltage change for a given change in current is the resistance $Rz$ of the Zener diode.
Beyond this threshold or cut in voltage, there is an exponential upward swing.
The typical forward voltage at room temperature with a current of around $1\ mA $is around $0.6\ V$ . In the reverse bias condition the Zener diode is an open circuit and only a small reverse saturation current flows as shown with change of scale.
At the reverse breakdown voltage there is an abrupt rapid increase in the current-the knee is very sharp, followed by an almost vertical increase in current.
The voltage across the Zener diode in the breakdown region is very nearly constant with only a small increase in voltage with increasing current.
There is a minimum Zener current, $I _{ Z }( min )$, that places the operating point in the desired breakdown region.
At some high current level, $I _{ ZM }$, the power dissipation of the diode becomes excessive beyond which the diode can be damaged.
Zener diode characteristics
The $I-V$ characteristics of a Zener diode is not totally vertical in the breakdown region. This means that for slight changes in current, there will be a small change in the voltage across the diode. The voltage change for a given change in current is the resistance $Rz$ of the Zener diode.
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