3V Constant Current Power Supply

3V Constant Current Power Supply
Some Engineering and Assembly Required

Discontinued - sold February 2000 through December 2002

Circuit boards are 1.65mm (.065") double-sided FR-4 with solder mask and silkscreen. All parts except LEDs are surface mounted.

All voltages and currents specified are design values. The actual values will differ due to production part tolerances.


The following modules consist of an LED array and associated power supply.

24-3V-(V2) Module

This module consists of a 24 White LED Array and a 24-3V Power Supply with wire leads.

The Red wire should be connected to the positive side of a 3V battery and the Black wire should be connected to the negative side of a 3V battery. Power consumption on the Overdrive setting is 4W.

The ribbon cable has a stripe along one edge. The wire sequence starting at the striped edge is Common, Off, Dim, Low, Medium, High and Overdrive. The switch position is selected by shorting the Common wire to the wire that corresponds with the desired setting. If more than one position is shorted, the position that corresponds to the highest setting will be selected.

Dimensions are 43mm by 36mm by 27mm (1.7" by 1.4" by 1.1").

Example Circuit

The following schematic shows one possible circuit for connecting up the 24-3V-(V2) module. This circuit is provided for illustrative purposes only.

23-3V module usage schematic

Example 24-3V-(V2) module interconnection

White LED Arrays

Our white LED arrays produce a white light with a color temperature of about 6500 degrees and a color rendering index of about 85. The light produced is similar to noon day sunlight in appearance.

LEDs have non-linear voltage/current curves (i.e., they don't act like simple resistors) and must be tightly controlled to produce predictable results. We recommend you always use our power supplies or a properly sized dropping resistor when driving our LED arrays to ensure proper behavior.

Large LED arrays can produce enough heat at high current settings to cause heat build-up in the array itself. What will happen is that as the array warms up, it draws more power, in a positive feedback mode. Over 20 to 40 minutes, the array can go into thermal run-away. Always provide some form of current limiting.

Always measure and test the final circuit to verify stable operation.

White LEDs lose efficiency as the power goes up. At one extreme, increasing the power by 7.5 times yields 3 times the light output while risking premature failure. The moral is to use more LEDs at lower power settings if you need more light.

24 White LED Array

This LED array contains 24 white LEDs arranged in an elongated hexagonal pattern. Four solder terminals are provided labeled HIGH, MED, LOW and GND. We recommend HIGH be connected to +400mA current source and GND be connected to the current source negative return. HIGH and MED are strapped. LOW is connected to an unpopulated resistor pad (1206 SMT to HIGH and MED). Nominal array voltage 3.2V to 3.8V.
CAUTION Do not allow the LED array to be driven above 400mA without appropriate thermal protection - otherwise the array will be damaged.

Dimensions are 43mm by 36mm by 16mm (1.7" by 1.4" by 0.7").

Power Supplies

These power supplies are designed to drive white LED arrays with the maximum possible efficiencies. These power supplies must be matched to an array with the specified number of LEDs. Unless otherwise stated, all power supplies have the following features:
  • Microprocessor controlled
  • Constant current
  • Automatic array temperature compensation
  • Automatic non-shorting LED failure compensation
  • 5 brightness levels
  • 2 f-stop brightness steps
  • Low brightness color shift compensation
  • Overdrive usage is limited to 20% average and 30 seconds continuous
  • SOS signal (one and a half full on/off cycles for set, off for release)
  • Switch lock (two full on/off cycles for set and release)
  • Polarity protection without blocking diodes (maximum of 60 seconds)
  • Supports multiple switch types and configurations by using highest setting from switch sensor (Off, Dim, Low, Medium, High, Overdrive)

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.

24-3V-(V2) Power Supply

This power supply takes input voltages from 2V to 3.8V and provides an output voltage of 3V to 4V as needed to drive a 24 white LED array. The power supply is capable of supplying 1.25A in the Overdrive setting.

The power supply automatically dims the higher settings to conserve power as the input voltage drops below 2V. The power supply requires a minimum of 1V to start functioning when batteries are connected but will then continue to operate down to 0.7V. If you are running at low voltages, do not disconnect the batteries until fresh batteries are available (or unless you are removing the batteries for long term storage).

The power supply may be connected to voltages as high as 4.6V. However, as the voltage rises above 4.1V the leakage current will increase but will remain below 1mA at 4.6V. Therefore, if you store the light for an extended period with the batteries connected, it will discharge the batteries down to 4.1V. This will happen over a period of weeks to months.

Four pre-wired solder terminals are provided labeled V+ (red), V- (black), VOUT (orange) and RTN (blue). We recommend V+ and V- be connected to a suitable power source and VOUT and RTN be connected to a suitable load. VOUT is positive with respect to RTN. There is no common ground.

The switch sensing detects when the switch common is connected to one or more of the switch sense pins. The switch pins are (top to bottom) Common, Off, Dim, Low, Medium, High and Overdrive

As the battery voltage drops below the minimum voltage the power supply will drop out of regulation gracefully.

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


Version 2: add microprocessor controlled constant current power supply with 5 brightness settings and other new features.

Version 1: 3V power supply (CV) product description.

Specifications are subject to change without notice.

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Trademarks and trade names are the property of their respective owners.
Updated August 2015