Regulated power supply

akunec · 3rd November 2006, 10:52 PM

Hey guys,

In this pic, i dont understand the diodes across the regulators. Since they allow current to flow from a higher voltage to a lower voltage in only one direction, wouldnt they essentially bypass the regulator?

Also, those diodes across the rails to the ground. Wouldnt those short out the rails to ground?

Thanks

jaudio · 3rd November 2006, 11:13 PM

http://focus.ti.com/lit/ds/symlink/lm317.pdf page 7

Maybe the last diodes are zeners?

I_Forgot · 4th November 2006, 01:09 AM

In both cases the diodes are normally reverse biased, so they will not short the output to the input or just short the output. The input to output connected diodes are there to protect the regulator from charge stored in large capacitances on the output side of the regulator. The diodes wired from output to ground are there to protect the regulator from current surges that might occur if you connect/disconnect or switch on/off an inductive load (such as a motor, relay, or solenoid).

If you have neither inductive loads that are switched or connected on the output side of the regulator, nor large capacitances on the output side of the regulator, you don't really need either diode. On the other hand, using the diodes is "cheap insurance" so it is sort of silly not to use them. Four diodes will set you back about $0.20.

I_F

AndrewT · 5th November 2006, 10:27 AM

Hi,
read thread
Marantz CD63 & CD67 mods list
start at post 4475 and read all about correct grounding of regulators.
The schematic you have drawn is electrically correct but the wiring is NOT done that way. It leads to noisy/buzzy/hummy speaker output.

BTW. the protection diodes are correct. To save the reg if power goes down. It is all explained in the datasheet.

3rd November 2006, 10:52 PM	#1
akunec diyAudio Member Join Date: Aug 2004 Location: Alberta	Regulated power supply Hey guys, In this pic, i dont understand the diodes across the regulators. Since they allow current to flow from a higher voltage to a lower voltage in only one direction, wouldnt they essentially bypass the regulator? Also, those diodes across the rails to the ground. Wouldnt those short out the rails to ground? Thanks

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Regulated DC power supply	Panicos K	Power Supplies	11	21st October 2006 12:32 AM
Regulated power supply	crissty	Chip Amps	23	2nd September 2005 04:18 AM
regulated power supply	yugaaa	Solid State	17	28th January 2003 02:39 PM
Using regulated power supply for A3	kirc	Pass Labs	4	25th October 2002 12:09 PM
regulated power supply	yugaaa	Solid State	3	17th June 2002 06:22 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

3rd November 2006, 11:13 PM	#2
jaudio diyAudio Member Join Date: Oct 2004	http://focus.ti.com/lit/ds/symlink/lm317.pdf page 7 Maybe the last diodes are zeners?

4th November 2006, 01:09 AM	#3
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	In both cases the diodes are normally reverse biased, so they will not short the output to the input or just short the output. The input to output connected diodes are there to protect the regulator from charge stored in large capacitances on the output side of the regulator. The diodes wired from output to ground are there to protect the regulator from current surges that might occur if you connect/disconnect or switch on/off an inductive load (such as a motor, relay, or solenoid). If you have neither inductive loads that are switched or connected on the output side of the regulator, nor large capacitances on the output side of the regulator, you don't really need either diode. On the other hand, using the diodes is "cheap insurance" so it is sort of silly not to use them. Four diodes will set you back about $0.20. I_F

5th November 2006, 10:27 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, read thread Marantz CD63 & CD67 mods list start at post 4475 and read all about correct grounding of regulators. The schematic you have drawn is electrically correct but the wiring is NOT done that way. It leads to noisy/buzzy/hummy speaker output. BTW. the protection diodes are correct. To save the reg if power goes down. It is all explained in the datasheet.