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Old 11th March 2012, 03:29 PM   #1001
Rush is offline Rush  United States
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Quote:
Originally Posted by UKToecutter View Post
Rush

Have a look at this post....

F5 power amplifier

and this one;

F5 power amplifier

I think you're right. We'll go for 1W

Andy
Yea, I think it is a peak current issue with the regular F5. But we are talking TURBO here and we expect current to be higher or why bother with TURBO?
I am out of my comfort zone making the next statement, but with V3 higher output power, all the feedback resistors should be looked at for more dissipation and maybe even higher wattage for R3 & R4 at some point.

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Old 11th March 2012, 03:46 PM   #1002
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Yes,

I've spec'd a 2W in the BOM's.
Mouser have a 2W that'll fit, DigiKey part will need to be tombstoned.
I'll increase the pad spacing for the second board batch.

Andy
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Old 11th March 2012, 03:48 PM   #1003
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110 Ohm !
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Old 11th March 2012, 04:42 PM   #1004
AndrewT is offline AndrewT  Scotland
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changing the upper leg of the NFB from 100//100 to 220//220 reduces the proportion of the power delivered to the lower leg of the NFB.
Do the sums.
eg
Max V Output ~ 40Vpk (100W into 8r0 or 200W into 4r0 per half channel).
total voltage across 10r + 220//220 = 40Vpk
Ipk ~333mApk

10r resistor instantaneous peak dissipation ~ .333^2 * 10r = 1.1Wpk
2W resistors would do, but I would go a bit higher. try 3W to 5W

220r resistor instantaneous peak dissipation ~.333/2^2 * 220r = 6W.
This parallel pair would need to be mighty for a +-45Vdc turbo.
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Old 11th March 2012, 05:35 PM   #1005
a.wayne is offline a.wayne  United States
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Interesting a 5 watter .....
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Old 11th March 2012, 05:56 PM   #1006
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Being a sinus, i think it's average power that counts into a resistor, not peak.
Or for square waves full blast measurement only.

Last edited by bobodioulasso; 11th March 2012 at 06:02 PM.
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Old 11th March 2012, 06:49 PM   #1007
AndrewT is offline AndrewT  Scotland
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instantaneous peak power will determine the maximum slope (slew rate) of temperature change in the resistor element (equivalent to change in junction temperature).
Since all normal Audio resistors have a non zero tempco, then the flatter the slope of the temperature then the better for the audio we are trying to pass.

Taken to the other extreme. Pass A constant DC current through the resistors. The slew rate of the temperature change is zero. Yes the resistor is at an elevated temperature but the resistance does not vary. That is the ideal that we are trying to achieve.

a quick reminder:
that example was for a 100W into 8r0 "half" turbo. That is a very big and powerful amplifier.
Quote:
Do the sums
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Last edited by AndrewT; 11th March 2012 at 06:51 PM.
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Old 11th March 2012, 07:21 PM   #1008
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Quote:
Originally Posted by bobodioulasso View Post
not peak.
STO.
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Old 11th March 2012, 07:43 PM   #1009
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Sorry,
what STO means?
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Old 11th March 2012, 07:47 PM   #1010
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Short-Term-Overload.

equivalent energy = actual energy * (1+ Pd/Pr)

Pd = Power dissipated
Pr = Power rating
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