Every circut board requires a power supply to operate properly. Usually, the power supply provides+5Vdc or +3.3Vdc to the whole circut board. There are also instances in which the power supply is not integrated to the circuit board and power must be provided by an external or separate power supply.
Overview
This project is a DIY DC power supply. It can provide a regulated +5Vdc or +3.3Vdc to any circuit board that requires external power supply. It uses two voltage regulators: one for +5Vdc and the other for +3.3Vdc. It also features power-indicating LED (light-emitting diode) and reverse-polarity protection diode.
Hardware
The circuit of this project is very basic. It includes a voltage source connector (JP1) which a regulated or unregulated power source can be connected. Mine is a 9-volt battery connector so that 9-volt batteries can be connected to my board.
When the voltage source or battery is connected properly or in correct polarity, current passes through 1N4001 diode (D1). The purpose of the diode is to block any negative voltage that may damage the whole circuit board.
The voltage that passed through the diode enters 7805 (IC1) which is a 5-volt regulator. This IC provides a constant and regulated +5Vdc output as long as its input voltage is within +7Vdc and +35Vdc.
Another voltage regulator is LM1117-3.3 (IC2) which is a +3.3-volt regulator. Its input is +5Vdc from IC1 and its output is a regulated +3.3Vdc.
Decoupling capacitors (C1, C2, C3) are also found in the circuit. These capacitors filter the inputs and outputs of each voltage regulator and they enhance the regulating capabilities of each voltage regulator.
The dual-row male header connectors (JP2 and JP3) included in the circuit can be used to provide power to different circuit boards that require +3.3Vdc or +5Vdc. The light-emitting diode (LED1) serves as a power indicator.
Build it…
If you want to build it, you may download the Eagle schematic and PCB files here.
How hot does your RM7805 get ?
mine gets pretty damn hot, almost burned my finger!
anyway, I can’t leave it on for more than 10 minutes for fear of melting the breadboard,
any suggestions ?
This is because the 7805 line of chips is a linear regulator. They basically regulate the input voltage down to the output voltage by dissipating the excess as heat. For any application that requires more than a couple miliamps, the 7805 will start to get hot. If you don’t do what I suggest below, you can buy a heatsink designed to fit on TO-220 packages and attach that to your 7805 to keep it cooler.
A cool chip that I’ve used is the OKI-78SR line of chips. They have 3.3V and 5V versions, and they are a switching drop-in-replacement for the 7805s. (switching=way higher efficiency than a linear regulator, drop-in-replacement means that it has the exact same pinout). The only downside is that they are a bit harder to find (try digikey or mouser) and will run you ~$4.00 vs the ~$0.50 of the 7805.
Would this circuit work with a USB connector as a Source Voltage?
Maybe instead of the LM7805 stage?
tx