"Cap Drop" Approach Implements Offline Power Supply for Light Loads
by Akshay Mehta, Texas Instruments, Electronic Design, Sep 12 2016
Focus:
The combination of a capacitor-dropper (cap-drop) circuit with a wide-input range buck
converter can serve as a low-power ac-dc power supply in energy meters and other applications
if transformer isolation is not required. The cap-drop circuit saves weight, size and cost
versus the conventional ac-dc supply. This short “Ideas for Design†article describes
operation
of two cap-drop circuits—a full-wave version using a bridge rectifier and a half-wave
version,
which delivers lower current. Suitable buck converter ICs are identified and safety concerns of
using a nonisolated design are discussed.
What you’ll learn:
- How to power MCUs and charge a battery in energy metering applications
- How to build a small, low-power ac-dc power supply for non-isolated applications
- How to reduce power consumption in energy metering applications
Notes:
After appearing online in September 2016, this article was published in print in ED’s April
2017 issue, pages 42-43.
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