[SOLVED] USB power supply for 8051 board

[arzade]

if i use USB - B type as a power supply for 8051 board .. it provides me only 3.03 v supply .
How to amplify to 5v for smooth working of board.

 

[wp100]

Hi,

Are you using a PC usb socket or a mains powered usb wall plug to provide the voltage ?

Both should produce +5v, so would seem something clearly wrong.

Are things getting hot, meaning you have a short circuit ?

 

[arzade]

actually in my board same usb pins are common for battery supply also

i have 1n4007 diode for safety . & hence when i use USB power supply .. diode drops the voltage

hence at the output pins of 7805 i am getting 3.03 v.

i added filter circuit too. but hardly changes in a circuit

 

[wp100]

actually in my board same usb pins are common for battery supply also

i have 1n4007 diode for safety . & hence when i use USB power supply .. diode drops the voltage

hence at the output pins of 7805 i am getting 3.03 v.

i added filter circuit too. but hardly changes in a circuit

Hi,

The output from a USB is +5v and its a reasonably stable supply.

However you will have to provide a different connection for it to the +5v VDD rail of your board, NOT the input to the voltage regulator

As you say if the USB +5v goes though the safety diode you drop 0.7v, and putting 4.3V though a +5v regulator that needs 7v minimum to produce a proper +5v is just plain wrong, hence your +3.03v

Do you have a schematic of your dev board to help show where you need to connect the USB +5v to ?

 

[arzade]

this is how i am using common pins for both battery & usb .
in this figure VCC line connect to 7805 through Diode 1n4007 .. which is not shown in figure

 

[wp100]

Hi,

This is how I would do things to give you a solid +5.0 volts.

The battery needs to be at least 9V to ensure the 7805 produces a good +5.0v

 

[arzade]

thank wp100 for this . i ll implement this & check ..