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32 The PCB Design Magazine • June 2015 Today, most of our printed circuit boards have at least a few DC-DC converters, and some boards have many. We have a large choice when it comes to deciding what to use: we can design and build our own converter from discrete parts (called voltage regulator down or VRD) or we can buy one of the off- the-shelf open-frame or fully encapsulated voltage regulator modules (VRM). For low currents we can use linear regulators; for me - dium and high current we are better off using a switching-mode topology. Whatever circuit best suits our needs, chances are that we want to keep the output voltage regulated against changes in input voltage and load current, which in turn calls for one or more internal control loops. There is a well-established theory to design stable control loops, but in case of power con - verters, we face a significant challenge: Each application may require a different set of out- put capacitors coming with our loads. Since the regulation feedback loop goes through our bypass capacitors (shown as a single Cout coulmn by Istvan Novak oRACLE QuIET POWER Avoiding Overload in Gain-Phase Measurements Figure 1: Block diagram of a typical DC-DC converter and gain-phase test setup.

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