All About Circuits Forum 7905 voltage regulator
 Register Blogs FAQ Members List Today's Posts Search Today's Posts Mark Forums Read

 Homework Help Stuck on a textbook question or coursework? Cramming for a test and need help understanding something? Post your questions and attempts here and let others help.

#1
04-15-2010, 04:52 PM
 jrekha Junior Member Join Date: Mar 2010 Posts: 11
7905 voltage regulator

Using 7905 voltage regultor can i produe +5V and -5V.
my Vin is 7V
#2
04-15-2010, 05:28 PM
 beenthere Senior Member Join Date: Apr 2004 Location: Missouri, USA (GMT -6) Posts: 15,815 Blog Entries: 10

No. If you had a source of -7 volts, you could produce a regulated -5 volts.
__________________
First comes the hardware, then the software.
#3
04-15-2010, 05:39 PM
 shivashankari.c14 Junior Member Join Date: Apr 2010 Posts: 10

u can produce -5v by using 7905...if u use 7805 u can produce +5v..
#4
04-18-2010, 05:59 PM
 jrekha Junior Member Join Date: Mar 2010 Posts: 11

so i need +5v and -5V, suplly is +7vand -7V.
how to do it using both 7805 and 7905?can i simply connect both together to respective supply, and ground together, to get the outputs??
#5
04-18-2010, 06:56 PM
 Bill_Marsden Super Moderator Join Date: Mar 2008 Location: Dallas, TX (GMT-5 w/ DST) Posts: 19,022 Blog Entries: 5

2 volts difference is pushing it a bit, but that is the idea.

You will need 0.1µF caps on the output of each regulator, as well as caps on the input (say 3.3µF) to keep the regulators from oscillating.

The 7805 and 7905 are pretty close to mirror images of each other. They both have overcurrent and thermal protections. If you push much current through them at all a heatsink is strongly encouraged. With a heatsink they are basically indestructible.

You also need a minimum load. If they will be disconnected from the circuit you might think about adding a 10ma LED circuit on them.
__________________
..
"Good enough is enemy of the best." An old engineering saying, Author unknown.

General info:
If you have a question, please start a thread/topic. I do not provide gratis assistance via PM nor E-mail, as that would violate the intent of this Board, which is sharing knowledge ... and deprives you of other knowledgeable input. Thanks for the verbage Wookie.
#6
04-18-2010, 07:54 PM
 Audioguru Banned Join Date: Dec 2007 Location: Ontario, Canada Posts: 9,411

7805 and 7905 regulators do not need a minimum load current. Their voltage regulation is spec'd with a load starting with 5mA but without a load the regulation is fine.

The LM317 adjustable regulator needs a minimum load current that is usually set with its veltage setting resistors.

 Tags 7905, regulator, voltage

 Related Site Pages Section Title Worksheet Zener diodes

 Similar Threads Thread Thread Starter Forum Replies Last Post tekinzen General Electronics Chat 18 11-27-2009 06:55 PM mikewashere05 General Electronics Chat 7 11-14-2009 07:16 PM DaMenaCe The Projects Forum 4 08-04-2009 06:56 AM n8ure The Projects Forum 26 02-03-2009 05:41 PM waver The Projects Forum 1 09-02-2008 03:24 AM

 Thread Tools Display Modes Linear Mode

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Electronics Forums     General Electronics Chat     The Projects Forum     Homework Help     Electronics Resources Software, Microcomputing, and Communications Forums     Programmer's Corner     Embedded Systems and Microcontrollers     Computing and Networks     Radio and Communications Circuits and Projects     The Completed Projects Collection Abstract Forums     Math     Physics     General Science All About Circuits Commmunity Forums     Off-Topic     The Flea Market     Feedback and Suggestions

All times are GMT. The time now is 03:19 AM.