Heat Dissipating Bus Bars for DC/DC Converter Output Stage
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Solution Overview
Problem
Conventional DC/DC switch mode power converters face issues with parasitic inductance and conduction losses due to the physical separation of transformer and synchronous rectifiers, limiting power density and switching frequency, and making it impractical to handle currents above 100 A efficiently.
Innovation Solution
A configuration using a printed circuit board, transformer, and bus bars that exposes bus bars to a cooling airstream, reducing the overall footprint and providing effective cooling and noise filtering, with bus bars acting as heat sinks and filter inductors to minimize losses and increase power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectifiers are implemented as MOS transistors in TO-220 packages attached to heat sinks, then cooling is provided, but the transformer and MOS switches cannot be placed in close proximity resulting in parasitic inductance and conduction losses
Solution Approach 1:
The bus bar integrates multiple functions into a single component: it serves as the electrical interconnection between transformer and synchronous rectifiers, while simultaneously functioning as a heat sink for cooling the MOS switches. This merging eliminates the need for separate heat sink components and reduces physical separation distance, thereby reducing parasitic inductance and conduction losses.
Solution Approach 2:
The bus bar performs multiple roles: electrical conduction, thermal management (heat sinking), and mechanical support for mounting synchronous rectifiers. This multi-functionality reduces the overall component count and allows closer placement of components, resolving the contradiction between reducing energy losses and managing device complexity.
2Power
If conventional TO-220 packages with heat sinks are used, then cooling is achieved, but the overall power density cannot be increased due to component size
Solution Approach 1:
By combining the interconnection function and heat sink function into a single bus bar component, the overall space required is reduced compared to using separate heat sink components. This allows for higher power density while maintaining effective cooling of the synchronous rectifiers.
Solution Approach 2:
The bus bar extends in multiple dimensions around the transformer, utilizing three-dimensional space efficiently. This spatial arrangement provides adequate cooling surface area while minimizing the footprint on the circuit board, enabling higher power density.
3Speed
If conventional packages are used, then synchronous rectification is achieved, but parasitic characteristics prohibit increase in switching frequency
Solution Approach 1:
The integrated bus bar structure minimizes the loop area between transformer and synchronous rectifiers, reducing parasitic inductance. This allows for higher switching frequencies to be achieved without excessive parasitic effects, enabling faster operation.
4Loss of energy
If transformer and synchronous rectifiers are placed in close proximity, then parasitic inductance is reduced, but effective cooling becomes difficult
Solution Approach 1:
The bus bar combines close electrical proximity (reducing parasitic inductance) with integrated heat sinking capability (providing effective cooling). The dual-function design allows components to be placed close together while maintaining adequate thermal management.
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 significantly increases power capability, reduces space requirements, and minimizes interconnection losses, enabling efficient handling of high currents while maintaining low noise and effective cooling.
Implementation Method 1
bus bars acting as heat sinks
Implementation Method 2
exposes the bus bars to the cooling air stream
Implementation Method 3
bus bars acting as heat sinks and filter inductors
Data Source
AI summary
A dense and efficient output stage for a DC/DC converter includes center tapped secondary windings of a transformer having an offset core with respect to a PCB, two pairs of synchronous rectifiers configured to define two pairs of paralleled symmetrical AC loops respective to the secondary windings, and at least two bus bars disposed within a forced cooling airstream to act as heat sinks for the synchronous rectifiers, while further providing a filtering impedance between the transformer windings and an output capacitance. A split capacitance is disposed in close proximity with the synchronous rectifiers to filter out ripple current, in one embodiment characterized by first and second capacitors each respectively coupled between opposing ends of the first and second bus bars, wherein the bus bars are arranged about at least three sides of the transformer core.