Dual Selectable Output Power Supply
Created: Apr 13, 2016
No description available.
A DC power supply is an electronic device that rectifies an alternating current into a direct current. Its purpose is to provide a DC power source to electronic devices such as diodes, transistors, ICs, etc., that require a constant DC source to operate. The advantage of using an electronic power supply instead of a battery is that, it can provide an unending and constant power source to a load as long as there is no power interruption and the load does not draw current that exceeds the limitation of the power supply. A basic power supply is usually composed of a transformer, rectifier, filter, voltage regulator, etc.
This reference design features a basic linear power supply that has two outputs in which the output voltage can be changed. The power supply per output is composed of 30VA VPP12-2400 transformer, 2A fuse, 1000V/2A TBS20M-TP bridge rectifier, 2200uF filtering capacitor, LM317DCYR adjustable voltage regulator, passive components, protection diodes, and dual binding post for the output. The transformer isolates the circuit on its secondary winding and step down the 220VAC from the primary winding to approximately 12VAC. The bridge rectifier rectifies the output of the transformer into a pulsating DC and the 2200uF aluminum capacitor filters the pulsating DC to make it smooth. The adjustable voltage regulator LM317DCYR regulates the voltage at its input pin to a certain voltage level depending on the resistance between its adjust pin and the ground. In this design, the LM317DCYR can change its output to 3.3V, 5V, 9V, and 12V. By using an ATmega328P-PU microcontroller and an ADG1604 multiplexer, the resistance between the adjust pin of the regulator and the ground can be changed by pressing the V1 (for output 1) or V2 (for output 2) push-button. The ADG1604 multiplexer has a common output (D) and four internal switches (S1-S4) that close individually based on the logic present on its 3-bit binary address line (A0, A1, EN), which is handled by the microcontroller. The switch S1 is assigned for the 3.3V, while the switch S2 is for the 5V output. The switch S3 handles the 9V output, while the switch S4 is for the 12V output. The output voltages (V1 and V2) present at the dual binding posts are displayed on the OLED graphic display. Also, a separate 5V power supply is added to supply the microcontroller, the multiplexer and the OLED graphic display.
This dual selectable output power supply can be used to power DIY projects that need two different levels of supply voltages. For example, the first output can be used to power a 5V microcontroller, while the second output energizes a 12V relay or drives a 12V DC motor. Each of the outputs can provide current up to 1.5A. A fuse is inserted between the secondary winding of the transformer and the bridge rectifier to serve as a protection in case the load draws too much current.