Feature: Power
Configuring switched-mode power supplies for high-redundancy applications
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By Alexander Mezin, Senior Field Application Engineer EMEA, SL Power Electronics Although there are different ways to wire load sharing with
here are many instances when more than one power supply is required in a system setup, governed by the need for more power, greater system reliability or mechanical constraints. Here are a few scenarios to consider:
Redundancy In critical applications where power must not fail, redundancy can be achieved by connecting two or more power supplies together. This setup requires that same-type supplies be connected in parallel to ensure identical operation, regardless of which unit will be connected to the load. Redundant sharing allows switching only the desired
number of power supplies in parallel at the same time. In case of a failure, the control circuit automatically switches over to another supply, to ensure continuous power delivery. Active redundant configuration allows to keep some of the connected supplies in parallel not loaded, to avoid stressing critical components. Such an approach also extends the life of the spare power supplies. Also, the current- or load-sharing circuit helps manage the output current evenly across all active supplies, greatly reducing stresses on each unit as well as allowing it to run cooler, resulting in higher overall reliability.
14 March 2022
www.electronicsworld.co.uk
parallel power supplies, the most common is the star wiring method; see Figure 1, left. The first configuration the figure offers is a basic level of
redundancy, without any extra components, which are not strictly necessary for load sharing. However, many safety- critical systems go a step further, demanding advanced redundancy that requires additional components, such as OR-ing diodes or MOSFETs; see Figure 1, middle and right. OR-ing diodes are a successful method in their simplicity,
but they have power losses, which most of the time can be neglected. The loses are even higher when using MOSFETs, but this setup is a lot more efficient.
Parallel operation There are many reasons why several power supplies should be connected in parallel instead of using higher-power units in modular configurations: when a wider power range is required, when there are mechanical limitations, or even lack of products meeting the desired specification. Specifying power supplies for parallel and redundant
operation is similar, but the control function differs. A single unit is clearly not sufficient here to provide the desired
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