Re-purpose your old mobile phone chargers into a triple output power supply for bread-boarding analog and digital circuits.

Mobile phone chargers which connect to the utility wall outlet are efficient switch-mode-power-supplies which convert the utility 110V/220V AC supply to 5V/6V DC with current ratings from 250mA to 1A and provide isolation from the AC mails.

Five chargers when suitably connected can form an excellent triple output power supply for bread-boarding analog and digital circuits.

Specifications:

Input AC 110V-240V 50/60Hz

Output 1 +5V DC 500mA Suitable for Digital IC's

Output 2 +12V DC 250mA Suitable for Analog IC's

Output 3 -12V DC 250mA Suitable for Analog IC's

The images show a demonstration of the power supply when used to power a typical analog/digital circuit being tested at bread-board level.

A LM555 timer IC is operated at +5V and forms the clock for a 74193 4-Bit binary counter. The counter outputs are fed to the 4 msb's of a DAC 0800 whose voltage reference is provided by a 9V regulator chip. The DAC output is fed to a LM741 OP Amp. The DAC and OP Amp operate with +/-12V

The Oscilloscope display shows the 4 counter outputs and the overall DAC output. https://www.instructables.com/id/DIY-USB-OSCILLOSCOPE-IN-A-MATCHBOX/ is used to capture the waveforms.

Caution: Mobile phone chargers operate at the mains voltage of 110V/ 220V and extreme care must be taken while building this unit.

Step 1: What You Need

Five mobile chargers are required. One of these must be a true 5V output unit suitable for digital circuits which have a strict supply voltage range.The other four could have a nominal voltage of 6V. These would be paired and used for the +/-12V output. Analog circuits typically accept a large supply voltage range and the nominal 12V could vary between 10-12V. Any voltage references would need to be separately derived from these voltages.

A plastic pencil box is suitable for this power supply as it would be well insulated from the mains voltage contained within the overall unit.

It is necessary to do a quick check to see that the five smps modules removed from the mobile charges fit comfortably within the box. Space must be catered for the switches connectors and wiring.

A mains patch cord, DPDT switch, output terminals and legs for the box are required.

Electrical tools, soldering iron and wires are essential to complete the wiring and assembly.

Step 2: Building the Unit 1:

Evaluation of the SMPS modules

The mobile charges available were of different types and ratings and it was necessary to evaluate them for input-output performance at 110V/220V AC input and different load conditions.

Based on the test results the module based on the TINY264 circuit was chosen for the +5V 500mA Digital supply.

The other units were paired to get the +/-12V Analog supply with one of the 'Morsing Make' circuits in each pair.

Connection Schematic

AC Mains is connected to the modules through a DPDT switch

The +5V module is independently used for the digital supply.

The other four +6V modules are paired with their outputs connected in series to form the +/-12V analog supply.