Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th May 2006, 12:38 PM   #1
diyAudio Member
 
Join Date: Aug 2005
Default 7805 5V regulator trouble!

So I bought the 7805 5V regulator for the digital voltage meter and wired it up.
After rectification, the voltage is about 27V
The 7805 says it operates up to 35VDC
I measured the voltage from the leads ouput and ground and it read 0!!

What am I doing wrong. I have the +output of the rectifier going into the 7805 input. Then the output of the 7805 goes to my digital volt meter. The volt meter and 7805 are grounded back to the rectifier.

I have to be doing something wrong, but I can't figure it!

Thanks guys,
Dominick
__________________
A real amateur enthusiast!
  Reply With Quote
Old 11th May 2006, 01:03 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
You need to load the 78/79 series regs a bit for it to work.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 11th May 2006, 01:24 PM   #3
diyAudio Member
 
Join Date: Aug 2005
Thanks for the reply, but I am still a very new amateur.

Can you please explain how to apply a "load"???

Thanks,

Dominick
__________________
A real amateur enthusiast!
  Reply With Quote
Old 11th May 2006, 01:54 PM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Put a resistor, like maybe 1k, on the output.

Bit puzzled what you are doing with the volt meter though. What are you measuring with the meter? With a 5V supply it probably won't measure more about 4.5V so seems pretty useless to me?
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 11th May 2006, 02:21 PM   #5
diyAudio Member
 
Join Date: Aug 2005
Richie00boy,

I tried the load idea, but I used an available 1.5k resistor and it did not change anything. The meters are brand new so I know it is not them.

Should I try a lower resistor?

Thanks,
Dominick
__________________
A real amateur enthusiast!
  Reply With Quote
Old 11th May 2006, 02:26 PM   #6
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
I know that some 7805's have different pinouts than others, depending on manufacturer. Has caught me once too.

Which pinout do you use? And can you post a drawing of your circuit?

Also, you need some capacitance at the output, see the data sheet, (you already have a cap on the input, right?) to avoid oscillation. Depending on the dig voltmeter, it may confuse eventual oscillation into zero volts.

Jan Didden
__________________
Never explain - your friends don't need it and your enemies won't believe you anyway - E. Hubbart
Check out Linear Audio Vol 7
!
  Reply With Quote
Old 11th May 2006, 08:30 PM   #7
cpemma is offline cpemma  United Kingdom
diyAudio Member
 
Join Date: Jul 2003
Location: S Yorkshire OK
Quote:
Originally posted by Dominick22
I tried the load idea, but I used an available 1.5k resistor and it did not change anything...Should I try a lower resistor?
The 7805 spec guarantees the voltage tolerance with loads 5mA to 1A; 5V/1k = 5mA, 1.5k gives 3.3mA. You should get a reading, but maybe not in the guaranteed 5V+/-0.25V range.

The resistor should be between the output pin and ground.
  Reply With Quote
Old 11th May 2006, 08:36 PM   #8
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
I think you should have wired something wrong.recheck all connections , pinout , etc.

Regards,
Lukas.
  Reply With Quote
Old 11th May 2006, 08:57 PM   #9
diyAudio Member
 
Join Date: Aug 2005
I sketched what I guess you could call a schematic of what I have set up that is not working.

I appreciate any feedback or suggestions!

Dominick

Click the image to open in full size.
__________________
A real amateur enthusiast!
  Reply With Quote
Old 11th May 2006, 09:07 PM   #10
Bazukaz is offline Bazukaz  Lithuania
diyAudio Member
 
Bazukaz's Avatar
 
Join Date: Nov 2005
Location: Vilnius
Send a message via Skype™ to Bazukaz
Where is the filter cap , directly after rectifier between + and ground ?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
When to use 317 and 7805? Sunsun22 Power Supplies 8 6th April 2009 06:47 PM
7805 regulator max input current adrianbodor Power Supplies 20 27th August 2008 10:18 PM
7805 trouble DragonMaster Power Supplies 4 23rd October 2005 02:38 PM
Very low noise 7805? ChuckT Digital Source 34 15th October 2005 02:47 PM
7805 to get 5V from car battery Morbid Parts 14 19th October 2004 07:39 AM


New To Site? Need Help?

All times are GMT. The time now is 11:26 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2