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Understanding PCB/FPGA power architecture (Part 1)

Posted: 07 Feb 2014 ?? ?Print Version ?Bookmark and Share

Keywords:FPGA? AC/DC convertor? imaging system? Switching regulators? Linear regulators?

Having determined the load power, we need to determine the overall power requirementsincluding loses in the power convertorsbefore we can specify the power required from the AC/DC convertor or DC supply.

Having determined the power required by each device, the next step is to determine the power required by each rail. This can subsequently be used to determine the conversion architecture, althoughof courseother requirements also come into play when determining this.

When it comes to the power architecture itself, there are two main types of convertors as follows:

Switching regulators generate the regulated output voltage by switching storage inductors into, and out of, the circuit to maintain a regulated output voltage. This switching is controlled via either an analogue or digital control loop. With a switching regulator, 100% efficiency is theoretically achievable. In the real world, however, components are not ideal, but efficiencies greater than 90% can be achieved and Gallium Nitride (GaN) power FETs promise even better performance.

Linear regulators generate the regulated voltage by dissipating the excess power across a pass transistor. This dissipation is managed via a control loop to adjust for fluctuations. Since there is no switching involved, the linear regulator is often used where quieter power supplies are required. However, this does not mean that all ripple on the voltage rail is rejected. As can be seen in the image below, the ripple rejection decreases as the frequency increases.

In my article on this topic, I will consider the advantages and disadvantages of switching regulators versus their linear counterparts, along with other considerations that must be taken into account to obtain a good, efficient, and reliable power architecture. In the meantime, I welcome your questions and comments.

About the author
Adam Taylor is the Head of Engineering Systems at E2V.

To download the PDF version of this article, click here.

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