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8th August 2009, 03:58 PM  #1 
diyAudio Member

Slew Rate Vs Frequency response
So, is anyone know here the colleration (equation?) about Slew Rate and Frequency response that is produced?
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8th August 2009, 05:37 PM  #2 
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Join Date: Apr 2006
Location: Minnesota

In general, there is not a one to one correspondence. Most audio amps have a capacitance that dominates the frequency response. Slew rate limiting occurs for large signals, because the current available to charge and discharge this cap is limited. Thus the name slew rate limiting. The small signal response is limited by the same cap, but for small signals the response is controlled by an RC time constant.

8th August 2009, 05:37 PM  #3 
diyAudio Member

Slew Rate Vs Frequency Response
sorry, I'm wrong on typing "colleration", its Correlation.
so what is the correlation (equation?)? Mr. Self says that SR 2.1V/us can produce 20kHz. http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm Mr. Elliott on his Project68 500W PA have a SR about 3V/us and can produce ~30kHz (not at full power) How about LM324 that is only have 0,4V/us SR? is it can only produce less than 4kHz?
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8th August 2009, 06:00 PM  #4 
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Join Date: Dec 2005
Location: Los Angeles

The conventional formula used for large signal slew rate limited response is F = Sr/2*pi*Vp. So for a slew rate of 7 V/uS (7*10 ^6 V/S) and voltage peak of 38 V the maximum frequency before triangulation occurs is around 29.3 KHz. Note that outright triangulation of a sine wave represents a rather severe state of affairs, and many prefer a slew rate that does not allow an amp to even come close to this condition.

8th August 2009, 06:03 PM  #5 
diyAudio Member

I think you mean fullpower bandwidth (rather than frequency response).
If you have a sinewave at an amplitude of A [volts] and frequency f [Hz], then its highest slew rate will be where it crosses zero volts and will be 2*pi*f*A [Volts/sec]. Divide by 1,000,000 to get it in Volts/usec. So, if you have a 100Watt power amplifier (40volts peak into 8 ohms), then for it to do an undistorted full scale sinewave of 40V peak at 20kHz, it needs to have a slew rate of at least 2*pi*20,000*40/1,000,000 = 5.03 V/usec 
8th August 2009, 06:21 PM  #6  
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Re: Slew Rate Vs Frequency response
Quote:


8th August 2009, 07:22 PM  #7 
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Join Date: May 2005
Location: SoCal

large signal SR =Iq/Cc
where Cc=miller cap at VAS and Iq= total collector current in half of long tail pair. ie max current to charge Cc. small signal fbw =SR/(2*PI*Vp) small signal limit, solve for Vp given Fbw=closed loop BW and SR Full power BW fFPBW is defined as the highest frequency at which the op amp can put out a sinewave with a peak voltage equal to Vclip. It is given by fFPBW =SR/(2*PI*Vp) where Vp= Vcliping reference http://users.ece.gatech.edu/~mleach/...5/tutorial.pdf
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8th August 2009, 07:33 PM  #8 
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Join Date: Nov 2008
Location: Brazil

The correct measure for squarewave:
http://www.falcosystems.com/high_vo...mplifiers.html  Rise Time must be (us), is the voltage peak to peak in (10%90%). What I would like to know what is valid to specify.......with or without filters( input RC and coil zobel ) ? 
8th August 2009, 07:36 PM  #9  
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Join Date: May 2005
Location: SoCal

Quote:
usually for both with (given if they are reasonable BW)
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10th August 2009, 02:17 PM  #10  
diyAudio Member

Re: Re: Slew Rate Vs Frequency response
Quote:
Quote:
@bwaslo: yes I mean fFPBW. if fmax=SR/(2*p*Vp), then fmax will go higher if the Vp in small value. what will hapen in LM324 case? distorted? @PMA: what is that mean? in small signal like OpAmp? @infinia: if SR=Iq/Cc what is the term (unit)? Ampere/Farad = V/us? thx folks for the attention. sorry for my dumb question, just a newbie.
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