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Advantages of sine amplitude converter

Posted: 21 Feb 2012 ?? ?Print Version ?Bookmark and Share

Keywords:power supply? zero-crossing? sine amplitude converter?

The goals of power supply technology are quite quantifiable. Systems designers are increasingly driven to extract the most from the available technology in terms of energy efficiency, performance, power density, and cost.

Energy efficiency goals are driven by thermal considerations in the equipment that the power supply is to serve, by overall system manufacturing and operating costs and, increasingly, by government regulation.

Performance goals for power supplies go well beyond providing the correct number of watts at a specified voltage; they span regulation over input and load range, dynamic response to load changes, and conducted and radiated noise. In compact systems, energy density is a very critical system design goal.

Cost per watt has always been an important metric applied to the bill of materials of power systems and energy costs per year are now commonly quoted for systems that are powered on a continual basis. In many systems, the idle (standby) or low power energy usage is also a significant consideration in total energy usage. Modern power supplies have evolved to meet these goals, with DC-DC converters providing the underlying technology.

The development of packaged DC-DC converters, starting in the 1980s, was a huge step forward in the evolution of DC power technology. The ability to generate local DC power busses with some degree of efficiency challenged the existing practice of a central power supply that generated all system voltage levels and distributed them throughout the system.

DC-DC converters enabled the distribution of power within a system in an entirely new mode. A central power supply generated a relatively high "distribution rail" that was routed around the system, and multiple DC-DC blocks converted the distribution rail to the locally required levels very near the point of load. This methodology has already evolved through several generations, but the DC-DC converter remains as the foundation technology.

Like most revolutionary technologies, the first DC-DC modules had some serious limitations that were inherent in the design and limited by components that were available to their designers.

Maximum achievable efficiency was limited; 70% efficiency was considered a very good figure and in fact represented a comparatively good outcome, considering that the alternative solution was a linear regulator. Where the difference between the input and output voltage was considerable, this was much better than could be achieved using a linear regulator where the voltage was dropped across a power device that dissipated power equal to the product of the voltage drop and the output current.

Some of the inefficiency in the first generation products was due to unavoidable ohmic losses in the semiconductor switches. Another large proportion was related to the less than optimal timing of the switching signals that sapped efficiency by wastefully discharging a sizeable portion of the reactive energy that was being delivered to the primary side of the circuit.

A third contributor to reduced efficiency was the limited frequency at which the converter could be switched. Frequency was limited by the power dissipation capability of the switch MOSFETs, which had to absorb large switching transients on every cycle. This low energy efficiency resulted in limited output power.

The other weakness of first generation DC-DC power supply modules was electrical switching noise. The switching of the inductive elements generated large spikes on the input rail and careful design of filters was necessary to keep this noise from propagating throughout the system. The spikes also contributed a third key weakness, reliability problems, especially with the switch MOSFETs.

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