PDA

View Full Version : Using 7806 for a 6v supply



kp_chd
02-16-2008, 08:04 PM
I went through the datasheet of 7806 and made connections like:

Pin 1--Vin (From a bridge rectifier connected to a 12v t/f)
Pin 2--ground
Pin3--Vout

Two small capacitors --- (Pin1-Pin2) and (Pin2-Pin3)

The problem is , the Vout is about 0.43 volts.And the Vin is about 5 volts

If i take the 7805 , the rectified dc is about 17 volts.

How to fix it?
Thank you in advance!

kishore2k4
02-17-2008, 04:15 AM
How much current are you pulling from it? Most of the fixed voltage regulators have some form of thermal current limiting but your case looks like a dead regulator, assuming your are testing it correctly.

The power dissipation of your circuit is (17V-5V)*Load Current which can be high and if there isn't proper heatsinking the regulator will be permanently damaged. Why don't you test it with a lower Vin or when you test your next regulator start with a lower voltage like a 6V winding (~9VDC)

kp_chd
02-17-2008, 10:52 PM
Thank you Kishore !


I did not check the current.
I am using a heat sink.

I started off with a 6v t/f
then a 9v t/f
and finally the 12v one.

but all give the same result :: Vout~0.4 v and Vin~5v

Guess you are right.Might be a dead regulator. Will check with another regulator and post back.

firoz
02-17-2008, 11:37 PM
LM317 rocks.

kp_chd
02-18-2008, 08:20 PM
@firoz sir
Will try it out!

@kishore sir

You were right. The regulator has some problem.
I used another piece and its working fine!

firoz
02-18-2008, 10:23 PM
actually LM317 si good as it can with stand for some good AMPS,
but if u don't need much amps and want to get 6v out of 7805,try this
http://www.mitedu.freeserve.co.uk/Circuits/Power/vvr.htm

* pls don't address with SIR,(i am still young yaar).. :-)

kp_chd
02-20-2008, 07:42 PM
OK! :D