- Ideal Diode Definition: An ideal diode is defined as a perfect diode without any flaws, operating perfectly in both forward and reverse biased conditions.
- Zero Resistance: In forward bias, an ideal diode has zero resistance, making it a perfect conductor.
- Infinite Current: An ideal diode can allow infinite current to flow in forward bias due to zero resistance, as per Ohm’s law.
- Infinite Resistance: In reverse bias, an ideal diode has infinite resistance, acting as a perfect insulator.
- Practical Importance: Understanding the ideal diode concept helps in modeling, debugging, and analyzing circuits, even though ideal diodes do not exist in reality.
An ideal diode is a perfect diode without flaws, operating ideally in both forward and reverse biased conditions. Its characteristics divide between these two modes.
Characteristics of Ideal Diode when Forward Biased
Zero Resistance
In forward bias, an ideal diode offers zero resistance to current flow, making it a perfect conductor. The ideal diode therefore has no barrier potential. This raises the question of whether an ideal diode has a depletion region, since resistance arises from the immobile charges there.
Infinite Amount of Current
This property stems from the ideal diode’s zero resistance in forward bias. According to Ohm’s law (I = V/R), if resistance (R) is zero, the current (I) becomes infinite (∞). Thus, an ideal diode in forward bias can theoretically allow an unlimited amount of current to flow through it.
Zero Threshold Voltage
The threshold voltage is the minimum voltage needed to overcome the barrier potential before conduction starts. Because an ideal diode has no depletion region, nothing must be overcome, so no threshold voltage exists and the diode conducts immediately when biased, as the green curve of Figure 1 shows.
Characteristics of Ideal Diode when Reverse Biased
Infinite Resistance
In reverse bias, an ideal diode is expected to completely block the flow of current. This means it behaves like a perfect insulator when reverse biased.
Zero Reverse Leakage Current
This property of the ideal diode follows directly from its infinite reverse resistance. Ohm’s law again applies, now in the form 
(the red curve in Figure 1): no current flows through the reverse-biased ideal diode, no matter how high the applied reverse voltage.
No Reverse Breakdown Voltage
Reverse breakdown voltage is the voltage at which a reverse-biased diode fails and starts to conduct heavily. The ideal diode’s infinite resistance blocks current flow no matter how large the reverse voltage, so reverse breakdown can never occur and a reverse breakdown voltage never arises. With these properties, the ideal diode behaves as a perfect semiconductor switch: open when reverse biased and closed when forward biased.
In reality, no perfect ideal diode exists. The concept still earns its keep.
The reason is: idealised models make analysis simpler, in engineering and beyond. For the ideal diode specifically, a designer, debugger, student or layperson can model and analyse a circuit without getting lost in second-order effects.
