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Variable DC Power Supply - MP1203

General Desciption

The MP1203 is a variable DC power supply to fit into the back of a IBM compatible PC. The main usage for the MP1203 will be in personal computers to provide DC power to any external self powered devices (eg. speakers normally requiring an AC adapter). It could be used to power a Microcontroller development system, thereby removing the need for an extra power supply. The unit derives its 12 Volt power source from a 3.5" drive connector. We can provide a 3.5" to hard drive adapter cable if required. The output voltage is adjustable to values of 3.0V, 4.5V, 5.0V, 6.0V, 7.5V, 9.0V and 12V. The MP1203 can also adjust the polarity of the output between positive tip and negative tip (This feature must be used with caution as a positive ring means that the case of the external device is no longer at the same potential as the case of the computer). Look at the futher applications section below for other uses of this device.


- Variable voltage output (3.0V to 12V as above).
- Multiple connectors on power lead allows
for many different devices to be powered. - PC bracket and 4-pin input connector allows
for easy installation into PC computers. - Adaptable to other uses and voltages, see below.

Electrical Characteristics

The MP1203 uses a LM317T linear regulator which has a maxium input voltage of +40V. If the input voltage to the MP1203 was raised it could not exceed +40V as the LM317T is internally limited. Thus the MP1203 can be modified to output different voltages given that the input voltage is changed and the resistors are changed. Current draw can be up to 1.5 Amps however the present heatsink will not support this if the voltage differential is over 3V.

Futher Applications

1. Can be used in a car by connecting direct to battery or through a lighter plug.
2. Can be used as a variable power supply by removing the PC bracket, boxing the unit and running from a plug pack or other DC supply.
3. Higher output voltages can be obtained by increasing the input voltage and changing the resistor values.
4. By using a larger heatsink higher currents and/or voltage differentials could be achieved.
5. The 14-pin header could be replaced with a multi posistion switch or pot to make changing the voltage easier.
6. The 4-pin square header could be replaced with a toggle switch to make changing the polarisation easier.

Pictures of the MP1203 unit

Front of the bare PCB

Front of the variable unit

Front of the fixed 12V unit

Back of the PCB

Standard DC cable

4-way DC cable

Pricing and Available Models

Basic unit: $5.00
Fixed 12V unit: $2.50
Hard drive adapter cable: $1.00

Note: Both the Basic and the Fixed 12V units include standard a DC power output cable which connects to the unit.

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