Principles Of A Linear Supply
Linear power supplies are much more reasonable or "forgiving" as the case may be. Linear supplies don't necessarily have to include the dreaded feedback loop, which is the main culprit that causes squealing in the output. One example of a class A, non-feedback linear power supply is shown below.
Seems so simple, right? To contrast, take a look inside the switching type next time you pull your case cover off. Remember to disconnect any power to the supply! What isn't shown here is the large and heavy power transformer (which just two inductors) and the full wave rectifier made with 4 diodes. The switching unit has the advantage of not using a large transformer or huge filter capacitors, as C would denote.
From left to right, the raw rectified AC enters and is filtered with C. The value of C for a 300 watt supply could easily be in the 10,000 to 33,000 micro Farad (uF) range and that would be a rather large and expensive piece. Next, a small fraction of the current, say 1/100th of the total, flows through the resistor R. This current feeds a Zener Diode, denoted by D. The Zener Diode sets up a constant voltage (i.e. 12 volts) and also rejects various AC ripple components. This base voltage feeds the base input of the NPN pass transistor Q and thusly, a regulated voltage spits out of the node labeled DC OUT.
Notice that there is no possibly way to take a small portion of the output and feed it back into the input. Hence, this circuit has zero feedback, and cannot squeal. Unlike the switching unit, when this circuit gets loaded with a strong power drain, the ripple merely increases, not a switching frequency in the megahertz range. Lastly, when this circuit powers up, there exists a delay (short, but its there) instead of WHAM! With the switching supply.
Summation
We find the OCZ Modstream to be a very interesting solution for any PC enthusiast. With features such as EZMod giving you a more managed wiring system and improved air flow within the PC or PowerShield EMI giving the computer an improved current stabilization, reduced electromagnetic interference and most importantly in a cleaner output to the hardware are definitely interesting facts for any high end user seeking for optimal results for their new computer.
 When purchasing a computer power supply, pay particular attention to the overall power rating. Switching supplies don't like to be run anywhere near their maximum limits, and that's when the Modstrean can come to play with its powerful 420W or the more advanced 520W version. In addition OCZ backs up the product with their 3 year powerswap replacement program eliminating all the endless return for repair loops.
In the next few weeks we will be taking a closer look at the midstream along with its competition but this next time we will perform several voltage and temperature tests in order to give you more technical results. If you're already spending $1000 or more on your new system, don't be cheap with the power supply! We recommend taking a closer look at the Modstream, it's a PC enthusiast's dream product.
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