The diode is a semiconductor device and is one of the most basic components in electronics. It has a unidirectional conductive nature, allowing current to flow in only one direction. This property makes diodes widely used in electronic circuits. However, there are a number of problems that arise when diodes are used in parallel, and this article will detail these problems and explain why they should not be used in parallel. We will explain three main aspects:
I. Manufacturing process deviations and the voltammetric characteristics of diodes
Parameter differences between diodes are one of the reasons why they cannot be used in parallel. Although manufacturers can do their best to ensure that the parameters are consistent between diodes, in practice these parameters can vary. For example, different manufacturing lots, temperatures and other factors may lead to differences in parameters such as current, saturation current and reverse saturation current.
The current-voltage characteristics of a diode are non-linear, as shown below
Very small voltage difference pairs lead to very large current differences.
When two diodes with identical voltammetric characteristics are used in parallel, the current of the two diodes will not be distributed according to the theoretical values due to the different voltage drops caused by manufacturing process deviations, which in turn results in an uneven distribution of current, and some diodes may exceed their permissible limits, which can also lead to diode damage.
If diodes with different voltage-current characteristics are connected in parallel, this may result in one of the diodes carrying most of the load, while the other diodes have almost no current passing through them, thus not achieving balanced current.
II. Temperature characteristics
The influence of temperature on diodes is significant and can affect their current-voltage characteristics and other electrical parameters. When diodes are used in parallel, the influence of temperature can lead to large differences in the current-voltage characteristics of the two diodes, which in turn leads to the diodes not being able to balance the current effectively.
When the current imbalance causes one diode to heat up severely and one diode not to heat up, this in turn aggravates the current imbalance and eventually leads to damage to one of the diodes.
III. Leakage current
When using diodes in parallel, leakage current is also one of the factors that can cause the current to be unbalanced. If two diodes with different leakage current levels are connected in parallel, the leakage current will cause the current not to be balanced effectively under reverse bias. The diode with the higher leakage current will carry more current, which may lead to one diode being overloaded and damaged. Furthermore, as the leakage current may vary from diode to diode, this may lead to an imbalance of the voltage between the individual diodes, which in turn may lead to the current not being balanced.
