Pre-Regulator Design Protects High-Voltage Power Supplies From Phase Faults (Part One)

by Jean-Paul Louvel, ON Semiconductor, Toulouse, France, How2Power Today, Jan 15 2015

Focus:
Power supplies for applications such as e-meters and high-power appliances designed to run from a three-phase supply must be able to withstand incorrect connection between phases that can cause very high voltages to appear at the input. To survive these faults, the main ac-dc power supply must be able to withstand an applied voltage of approximately double the mains RMS supply voltage. For a system operating in the U.S., a switched-mode power supply (SMPS) with universal input can meet this requirement. But in Europe or Asia, the SMPS must be capable of withstanding an applied voltage of 460 V (over 600 V dc when rectified) which requires circuit modification to achieve a fault-tolerant supply. This article discusses several conventional methods for doing so (such as use of series-connected high-voltage bulk capacitors and high-voltage MOSFETs) and their limitations. This leads to the introduction of a pre-regulator topology that simplifies circuit design and component selection and saves costs while ensuring high efficiency and reliability.

What you’ll learn:

• How to protect switched-mode power supplies against high-voltage (460 V ac) phase faults
• How to simplify the design of fault tolerant switched-mode power supplies for e-meters and high-power appliances through the use of a 200-V pre-regulator circuit

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