This tutorial explains how to make your own power supply unit for all your electronics and embedded system experiments. It also has a backup battery which will be used in case of power cuts and a display. For this project Reader should have knowledge of How to start with AVR and interface LCD with AVR.
– Inputs: 220-240V, 50Hz AC
– Outputs: 1 X 5V and 1 X 9V (available through banana jack)
1 X Adjustable voltage (available through screw terminal)
– Adjustable Voltage Range:1.25-14.5V in Mains Mode and 1.25-10.5V in Battery Mode
– Modes: 1) Battery Mode and 2) Normal Mode (Through Mains)
– Automatic Switching and Shutdown by Microcontroller
– LCD with various indicators.
Fig. 1: Block Diagram of Un-interruptible Bench Top DC Power Supply
Fig. 2: Circuit Diagram of AC Rectifier used as first stage of Un-interruptible Bench Top DC Power Supply
Fig. 3: Circuit Diagram of Charger used as second stage of Un-interruptible Bench Top DC Power Supply
Charge Indicator: This is nothing but two resistors arranged in the form of a voltage divider circuit. It scales down the voltage level of battery for the microcontroller to read it.
Relay 1: This is a relay module which switches between the charge indicator circuit and charger circuit depending on the command from microcontroller.
Relay 2: This relay module switches between mains supply and battery supply depending on the command from microcontroller.
Fig. 4: Circuit Diagram of Charge Indicator used as third stage of Un-interruptible Bench Top DC Power Supply
Note: The +12V for powering the relay is given directly from the battery. This allows the relay to function purely based on the command from microcontroller instead of availability of power.
DC PSU: This block consists of the voltage regulators and a bunch of capacitors. +5V, +9V and adjustable voltage levels are provided by the ICs 7805, 7809 and LM317 respectively.
Fig. 5: Circuit Diagram of Voltage Regulators used as final stage of Un-interruptible Bench Top DC Power Supply
Panel Display: This is the front and outer panel block which consists of the main switch, LCD displaying the voltage level, Potentiometer Knob to adjust the voltage, Banana connectors and screw terminals.
This is how I want it to look like:
Fig. 6: Image representing Panel Display of Un-interruptible Bench Top DC Power Supply
The icons on the LCD indicate the following:
Fig. 7: Image showing Icons used on display panel to show different battery statuses
Fig. 8: Image representing pin diagram of character LCD
Since in the last step, the mains is unavailable anyways, the power to micro-controller board, LCD and the DC PSU gets cut off and hence the unit cannot be turned ON again without providing it the supply from mains.
Filed Under: Circuit Design