3V Constant Voltage Power Supply


3V Constant Voltage Power Supply
Some Engineering and Assembly Required

Discontinued - sold May 1999 through February 2000

Circuit boards are 1.65mm (.065") double-sided epoxy boards with solder mask and silkscreen. All parts are surface mounted.

All voltages and currents specified are design values. The actual values will differ due to production part tolerances. We recommend you measure the actual values and compensate for differences to assure proper operation of your final assembly. We recommend you only purchase LED arrays and corresponding power supplies as prewired assembled modules.

These power supplies are designed to drive white LED arrays with the maximum possible efficiencies. Therefore, these boards are designed without blocking diodes and will be destroyed if power connections are made incorrectly. Be careful to always maintain proper battery polarity.

We conformal coat power supply boards to improve water resistance in damp conditions and to increase the structural integrity of certain parts. However, the boards are not waterproof. Although we specify the solder terminal labels, the labels are not visible through the conformal coating and the corresponding wire color must be used instead as the sole reference.

This power supply takes input voltages from 1.5V to 3.0V and provides an output voltage of 3.2V or 2.95V to drive a white LED array. Four pre-wired solder terminals are provided labeled V+ (red), VSEL (yellow), VOUT (orange) and GND (black). We recommend V+ be connected to a suitable power source, VSEL be connected to V+ using a switch to allow mode selection by the user, VOUT be connected to a suitable load and GND be connected to the common negative ground. VOUT is positive with respect to ground.

The power supply can be run in two different modes: high power and low power. The high power mode is selected when VSEL is not connected and works as follows: if the input voltage is above 2.3V the power supply can provide 700mA at +3.2V. Otherwise, the power supply can provide 200mA at +2.95V. The low power mode is selected by connecting VSEL to V+ and when so configured, the power supply can provide 200mA at +2.95V at all input voltages. Efficiencies exceed 95% when driven at 2.8V.

The 2.3V set point is used to detect a dying lithium/sulfur dioxide battery. The power supply provides a step transition when switching from high power mode to low power mode. However, abnormally high battery circuit resistance can cause a flickering transition instead of a clean step transition. The abnormally high battery circuit resistance is normally caused by poor switch and battery contacts or undersized wire between the battery and power supply. This flickering is not harmful - only annoying - and it does get your attention. If you have installed a switch to select the low power mode, select it now to stop the flickering. Otherwise, the flickering will stop when the battery voltage stabilizes below the reset voltage. In any case, you should find a convenient place to change the battery.

The low power mode will continue to operate past the normal battery cutoff voltage of 2.0V. After the battery voltage drops below the supply limit, it will fall out of regulation and the output voltage will drop as the battery voltage drops.

Dimensions are 43mm by 36mm by 10mm (1.7" by 1.4" by 0.4").

Example Circuit

The following schematic shows one possible circuit for connecting up a working lamp using the large power supply and the 24 white LED array. This circuit is provided for illustrative purposes only.

Power supply usage schematic

Example power supply and 24 white LED array interconnection

Specifications are subject to change without notice.


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Updated February 2021
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