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How does an LED Emergency Tube Light work?

Updated: Jun 19, 2022

LED emergency products like Tube Lights and bulbs are becoming very popular as these become elegant solutions for the situations where you can expect the AC power to go down sometimes from a few minutes to a few hours and you do not want the house to go into total darkness. If you wish to buy this product please click the picture above or follow the link here.

Today let us look at how this product works and solves this application so elegantly and at a reasonable price level. Please refer to the schematic below with notes marked on it for ease of understanding.

In addition to a typical HPF SMPS driver circuit at the top of the schematic the following blocks have been added to yield the special emergency light features:

  1. Lithium Battery

  2. Battery Charger

  3. AC Fail Detector circuit

  4. DC LED Matrix

All the four blocks are controlled very elegantly by a single IC SIC9321. The data sheet of this IC is available below in case you are interested in downloading it.

SIC9321 (SOP-8)_EN_Rev1.4
Download PDF • 550KB

This IC works with a low voltage DC up to 6V and is ideal to work off a supply matching the typical Lithium battery voltage of 3.7V. This auxiliary voltage is derived very elegantly in this circuit solution by placing an auxiliary winding on the same transformer which is used as an inductor for the main AC circuit.

Arun Bhatia

16th August 2021

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