PSU3 - MC34063A
PSU3 - Power supply - MC34063A
Description:
Fig. 1 PSU3
This power supply is used to power various boards with onboard regulator. It is designed to provide enough voltage to a standard 5V regulator (7805).
To be portable, it is powered from a USB port and uses a MC34063A switching regulator in step up configuration to provide 8V.
Specifications:
Input voltage5V, USB
Output voltage8V
Max output current600 mA
ProtectionsOver current
EfficiencyOver 80%
Schematic:
The schematics are based around the datasheet of the MC34063A. The board is powered by a USB bus via a USB A connector on a cable. Capacitor C1 filters the 5V input voltage from USB.
R1 and R2 in paralell gives a 0.5 ohm value, which limits the output current to 600mA.
The output voltage is determined by the divider R4 and R5. It is determined by the following formula: Vout = 1.25 x (R5/R4 + 1). The choosen value will give an output voltage of 8V.
D1 is best being a fast Scottky rectifier for better efficiency.
Fig. 2 PSU3 schematic
R6 is here to have an easy Gnd point to connect a test instrument.
Construction:
The PCB fit on a small single sided board. You can also use a prototyping board.
Fig. 3 PSU3 layout
The leads from the USB cable are soldered on K1 on one edge, and the output connector on the other. Start with the lowest components of the board, and continue with the higher ones.
R6 is made up of a piece of resistor's lead. It's here to easily attach a clip from a test instrument or have a Gnd test point.
My version is built on prototyping board. I had an old USB cable with just the A type connector left on it. I soldered its lead on K1. I used for the output a cable from a small transformer block with different connector and fitted the board.
| PSU3 Component list |
|---|
| C1: 100 uF C2: 220 pF C3: 10 uF R1, R2: 1 R3: 220 R4: 2.2 K R5: 12 K R6: resistor's lead IC1: MC34063A D1: 1N5819 L1: 100 uH K1: 4 pins header K2: Connector AMP MT 2pins male |
How to use / Testing:
To check the power supply, plug the USB cable in a computer.
Just check that the output voltage on K2 is about 8V.
To use, just plug in the usb cable, and your project board with a cable (Check the supply voltage of your target first !).
Files and links:
Eagle PCB and schematics files for PSU3.PDFs of PCB, layout and schematics of PSU3.
Texas Instruments MC34063A.