Lm7805

D

dramrattan

Member

• Apr 15, 2009

• #1

Hi,

I'm using the LM7805 to get a steady 5V at the output when i used a 12V at its input. I connected it as shown on page 21 of the attached document but i don't know why those value capacitors were choosen.

What would happen if i change one of the capacitor values?...I don't have any spare to try it out and see for myself...How does this LM7805 work?

 

forumlicker007

New Member

• Apr 15, 2009

• #2

Where os tje attached document. They are smoothing capacitors to work with the 7805. Little changes won't be a problem.

 

N

neoandrewson

New Member

• Apr 15, 2009

• #3

7805 works fine from 100nF to 10uF without any problem.

 

audioguru

Well-Known Member

Most Helpful Member

• Apr 15, 2009

• #4

The capacitors stop the regulator from oscillating.

 

D

dramrattan

Member

• Apr 15, 2009

• #5

Thanks and sorry for forgetting to upload the datasheet.

 

D

dramrattan

Member

• Apr 16, 2009

• #6

The purpose of the diode is for protection?

 

Attachments

• Power Supply.doc

  383.5 KB · Views: 199

Last edited: Apr 16, 2009

J

Junker_eu

New Member

• Apr 17, 2009

• #7

The diode prevent the circuit from being supplyed in reverse.

 

audioguru

Well-Known Member

Most Helpful Member

• Apr 17, 2009

• #8

It is called an IDIOT diode. It prevents damage from an idiot who connects an input with the wrong polarity.
Sometimes a huge IDIOT diode is connected across the power input (in parallel) to blow the fuse when an idiot connects an input with the wrong polarity.

 

blueroomelectronics

Well-Known Member

• Apr 17, 2009

• #9

A crowbar circuit is handy for battery powered devices as you don't have a voltage drop from an inline diode.

 

Hero999

Banned

• Apr 17, 2009

• #10

IT doesn't matter if it's in series with a regulator and the dropout voltage isn't a problem.