Feedback resistor when using bridge mode

-_nando-_ · 17th May 2006, 04:53 AM

Hi everyone !

I read all the BPA200 datasheet, because I'm building it, and of course I know the manufacturer of the chip is right, BUT I DON'T understand why the feedback resistor (in red) is placed there !

The amp is used in inverse mode, so input signal enters in the inverse input, to have a inverse output to be connected to the -V of the speaker, and wow, you have the bridge!

The normal implementation (non inverted) use the feedback resistor to compensate the signal in, with the inverted signal, so, more feedback in the inverted input, less loud the sound will be...

So, WHY the inverted implementation don't use the feedback resistor connected to the non-inverted signal in? It don't make any sense to me...

Anybody ?!

Thanks !!

rpapps · 17th May 2006, 05:29 AM

Hi
The purpose of Rf & Ri in all four stages is to set the gain in accordance with the formula:
Vout/Vin = 1 + Rf/Ri
In this case, voltage gain is 22 or approximately 27 dB.
(Besides, if you connected the feedback to the non-inverting input you would have positive feedback, not negative. Oscillator anyone?)
Cheers
Rob

Greg Erskine · 17th May 2006, 05:59 AM

DELETED.

Sorry, I didn't read the post carefully and posted an inappropriate answer.

rpapps · 17th May 2006, 06:22 AM

Hi Greg, no need to apologise.
You were absolutely correct in what you said. I just used one formula to keep things simple. However, in practical terms, it makes less than a 1/2 dB difference which can be safely overlooked.
Cheers
Rob

17th May 2006, 05:59 AM	#3
Greg Erskine diyAudio Member Join Date: Jan 2002 Location: Sydney/Australia	DELETED. Sorry, I didn't read the post carefully and posted an inappropriate answer. __________________ Greg Erskine

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
Loudspeakers in Bridge Mode	losaavedra	Multi-Way	1	15th June 2009 09:36 AM
Difference between Bridge & Parallel mode	john_lenfr	Chip Amps	13	4th July 2005 01:27 PM
How to use STK459 in bridge mode	tridibesh	Solid State	0	4th June 2005 07:40 AM
Inverted gainclone with noninverted bridge mode	akunec	Chip Amps	0	20th October 2004 12:30 AM
bridge mode for LM 3875	partyjups	Solid State	2	5th June 2001 05:49 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

17th May 2006, 05:29 AM	#2
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Hi The purpose of Rf & Ri in all four stages is to set the gain in accordance with the formula: Vout/Vin = 1 + Rf/Ri In this case, voltage gain is 22 or approximately 27 dB. (Besides, if you connected the feedback to the non-inverting input you would have positive feedback, not negative. Oscillator anyone?) Cheers Rob

17th May 2006, 06:22 AM	#4
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Hi Greg, no need to apologise. You were absolutely correct in what you said. I just used one formula to keep things simple. However, in practical terms, it makes less than a 1/2 dB difference which can be safely overlooked. Cheers Rob

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)