Small LED string power supply

Background:

Last year I purchased a small LED lighting strip as a Christmas decoration. It was powered by two 1.5v batteries and whilst the lighting strip gave an effective display I found that the batteries didn't last too long. This year I investigated an alternative 3 volt power source and I also wanted to make use of some spare components I had.

I had a 240 volts (AC) mains power block for providing 5v DC to charge Sony Ericsson mobile phones and using this as the primary power source I investigated a suitable 3 volt regulator. The LP2950-30 provided the solution. I put together the simple circuit below. LED D1 provides an indication that the 5v supply is available. Capacitors C1 and C2 provide stability of operation for the voltage regulator as recommended in the LP2950-30 datasheet.

Specifications:

Input voltage supply 5v @ 450mA Sony Ericsson power block.

Output voltage 3v @ 100mA (max), to supply 50mA for LED string.

5v to 3v voltage converter circuit

Construction :

The circuit components were mounted on a very small piece of veroboard, placed within a small plastic box - Hammond 1551GBK.

To maintain separation of input and output connections, a 2.5mm DC power socket was used for the 5v input supply with a 2.1mm DC power socket used for the 3v output supply. The LED was mounted next to the input socket to act as a reminder that the neighbouring socket is for 5v input.

Operation:

The LED strip connects to the output socket using a 2.1mm DC power plug. The 5v power block connects to the input socket using a 2.5mm DC power plug. A regulated and stable 3v was measured at the output, with current draw of 51mA. Initially running for an hour with the plastic box lid fitted, the regulator was cool to the touch - working well below its maximum current capability. No more batteries will be required! Images of the completed unit are below:

Circuit board mounted within small box

Lights are on, no more batteries!!

Components:

LP2950-30 (3v Regulator)

2.2uF 50v Electrolytic capacitor (2)

D1 - Red LED as main power supply indicator

LED panel mounting socket

R1 - 220 ohms 0.25w

Supply input socket 2.5mm DC socket

Supply input plug 2.5mm DC plug to connect 5v power block

Supply output socket 2.1mm DC socket

Supply output plug 2.1mm DC plug to connect to LED string cable

Plastic project box Hammond 1551GBK 50x35x20mm

Veroboard for circuit mounting