Polyphase Alternator Rectifier Bridge Leakage Current Reduction
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Solution Overview
Problem
Conventional diodes in current rectifier bridges for polyphase alternators have high threshold voltages, leading to significant leakage currents, especially at elevated temperatures, which can drain the vehicle battery when the alternator is not ventilated.
Innovation Solution
Incorporating a pair of diodes in each branch of the rectifier bridge, where one diode has a very low threshold voltage (Vf) and high leakage current, and the other has a low threshold voltage with lower leakage current, with the low leakage diode mounted on the colder heat sink to minimize total leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional diodes with high threshold voltage are used in the rectifier bridge, then the leakage current is higher especially at elevated temperatures, but the manufacturing is simpler and more straightforward
Solution Approach 1:
The patent divides each rectifier bridge branch into two separate diodes connected in series: a first diode with high threshold voltage and a second diode with low threshold voltage. This segmentation allows each diode to be optimized for its specific function - the first diode blocks reverse current while the second diode minimizes forward leakage current, resolving the contradiction between low leakage and manufacturing simplicity.
Solution Approach 2:
The patent changes the threshold voltage parameter of the diodes by selecting two different diode types with distinct threshold voltage characteristics. The first diode has a high threshold voltage (e.g., 0.7V or higher) while the second diode has a low threshold voltage (e.g., 0.3V to 0.5V). This parameter differentiation enables the system to achieve both low leakage current and manageable manufacturing complexity.
2Loss of energy
If a single diode with low threshold voltage is used to reduce leakage current, then the threshold voltage is lowered but the leakage current increases at elevated temperatures
Solution Approach 1:
The patent segments the diode function into two specialized components: a first diode optimized for high-temperature stability with high threshold voltage, and a second diode optimized for low leakage current with low threshold voltage. This segmentation allows each component to excel at its specific function without compromising the other, resolving the contradiction between low leakage and temperature stability.
Solution Approach 2:
The first diode with high threshold voltage acts as an intermediary that protects the second diode with low threshold voltage from high-temperature effects. The first diode blocks reverse current and isolates the second diode from voltage spikes and thermal runaway, allowing the second diode to maintain low leakage current without suffering from temperature-induced reliability issues.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces the overall leakage current and enhances the efficiency of the alternator by lowering the threshold voltage while minimizing battery discharge.
Implementation Method 1
one diode, called the first diode, has a threshold voltage lower than the threshold voltage of the other diode, called the second diode
Implementation Method 2
the leakage current of the second diode is lower than the leakage current of the first diode
Implementation Method 3
the low leakage diode mounted on the colder heat sink to minimize total leakage current
Implementation Method 4
one of the diodes, called the first diode, has a threshold voltage lower than the threshold voltage of the other diode, called the second diode
Data Source
Figure 1~3
Figure 4~6
AI summary
The invention relates to a rectifier bridge for a polyphase alternator having a polyphase armature winding including phase outputs, said rectifier bridge including several parallel branches, each including a pair of diodes (80, 100) mounted in series and a connection point (114) to be connected to one of the phase outputs (23) of the armature winding, at least one of the branches thereof comprising two diodes (80, 100) having a threshold voltage (Vf) lower than 0.7 V, wherein one so-called first diode (80) has a threshold voltage lower than the threshold voltage of the other so-called second diode (100), and a leakage current higher than that of the first diode (80). The alternator is provided with at least one such bridge.