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Improved Load Current Capability for Cap-Drop Off-Line Power Supply for E-Meter

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Standard electronic electricity meters (e-meters) have traditionally used a capacitive-drop power supply (capdrop) plus linear regulator topology to provide a cost-effective power supply. Today, opposing forces such as an increase in load currents due to more complex AMR and AMI ommunications circuitry and tighter power consumption regulations, force e-meter designers to limit consumption to below 4VA (~1.2W) for single-phase or 8VA (~2.4W) for 3-phase e-meters. employing an innovative, yet simple, solution using a switching DC/DC converter, such as the TPS5401 in place of the linear regulator allows the e-meter designer to avoid the costly move to expensive switch mode power supply (SMPS) solutions. This application note goes through the step-by-step decisions a designer must make to complete a cap-drop power supply with a DC/DC converter. A design calculator tool, SLVC392, is also available with the application note to assist the designer, when the design criteria are different than the application note.