Switching power supplies are known for high efficiency. An adjustable voltage/current supply is an interesting tool, which can be used in many applications such as a Lithium-ion/Lead-acid/NiCD-NiMH battery charger or an standalone power supply.

Features

• Cheap and easy to build and use
• Constant current and constant voltage adjustment [CC, CV] capability
• 1.2V to 25V and 25mA to 3A controlling range
• Easy to adjust the parameters (optimum use of variable resistors to control the voltage and current) 
• The design follows the EMC rules (input and output are on the same edge, means lower voltage difference and lower EMI)
• It is easy to mount a heatsink on the LM2576
• It uses a real shunt resistor (not a PCB track) to sense the current

You can apply the maximum voltage of 30V to the input. The LM2576-Adj (PS1) can accept input voltages up to 40V, but REG1 (78L09) can tolerate the maximum of 35V (absolute maximum rating) at the input. REG1 plays an important role in the stability of the amplifier (IC1), therefore reducing 10V from the input voltage threshold is a wise decision.

To set your desired voltage, simply connect a voltmeter (or a multimeter in the voltage setting) to the output and turn the R6 multiturn potentiometer. To set your desired current limit, simply connect an ammeter (or a multimeter in the current setting) to the output and turn the R7 multiturn potentiometer to set your desired current limit. Do not prolong this process because holding the output on the short circuit condition is not recommended.

Schematic

PCB

Bill of materials