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Old 8th August 2009, 03:58 PM   #1
kroto is offline kroto  Indonesia
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Default 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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Old 8th August 2009, 05:37 PM   #2
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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.
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Old 8th August 2009, 05:37 PM   #3
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Default 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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Old 8th August 2009, 06:00 PM   #4
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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.
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Old 8th August 2009, 06:03 PM   #5
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I think you mean full-power 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
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Old 8th August 2009, 06:21 PM   #6
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Default Re: Slew Rate Vs Frequency response

Quote:
Originally posted by kroto
So, is anyone know here the colleration (equation?) about Slew Rate and Frequency response that is produced?
Sorry, not necessarily any correlation, if speaking in small signal terms.
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Old 8th August 2009, 07:22 PM   #7
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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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Old 8th August 2009, 07:33 PM   #8
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The correct measure for square-wave:

http://www.falco-systems.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 ) ?
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Old 8th August 2009, 07:36 PM   #9
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Quote:
What I would like to know what is valid to specify.......with or without filters( input RC and coil zobel ) ?

usually for both with (given if they are reasonable BW)
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Old 10th August 2009, 02:17 PM   #10
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Default Re: Re: Slew Rate Vs Frequency response

Quote:
Originally posted by bwaslo
I think you mean full-power 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

Quote:
Originally posted by PMA


Sorry, not necessarily any correlation, if speaking in small signal terms.

@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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