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Old 28th December 2011, 07:52 PM   #301
Pano is offline Pano  United States
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Originally Posted by tvrgeek View Post
I finally got the picture using two meter probes as a delay line and a 1/2 meter as the trigger.
Clever!
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Old 28th December 2011, 07:52 PM   #302
tvrgeek is offline tvrgeek  United States
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Standard remote control IR runs between 36 and 56 Khz carriers with a few odd-balls running as high as 70K. What the actual diodes can do I have not looked at. Considering that are talking about 10Base Ethernet being piped over the LED overhead lights, I would suggest there is some room there.
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Old 28th December 2011, 08:01 PM   #303
a.wayne is offline a.wayne  United States
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Err, can i interupt a bit here, Sy and others are you saying that a/ab SS amps don't suffer from Temperature induced distortion, when temperature tracking ..?

Last edited by a.wayne; 28th December 2011 at 08:10 PM.
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Old 28th December 2011, 08:06 PM   #304
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Which matters most: chip surface instantaneous temperature, or junction instantaneous temperature? A bit of dynamic thermal modelling would give a connection between them, but a zero result from aiming an IR diode at the chip surface is not sufficient to show that nothing is happening at the junction (in the absence of such a thermal model). At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.
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Old 28th December 2011, 08:10 PM   #305
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Quote:
Originally Posted by DF96 View Post
At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.
That gets back to my original observation about the lack of distortion rise with lower frequency.
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Old 28th December 2011, 08:12 PM   #306
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Quote:
Originally Posted by DF96 View Post
Which matters most: chip surface instantaneous temperature, or junction instantaneous temperature? A bit of dynamic thermal modelling would give a connection between them, but a zero result from aiming an IR diode at the chip surface is not sufficient to show that nothing is happening at the junction (in the absence of such a thermal model). At the very least a junction thermal time constant would be useful, giving a first-order thermal low pass filter.
Right. And junction itself is the best tool to measure own temperature directly. Chemist SY knows physics well. But moderator SY wants the show to go on, I suppose. All topics where he participates are usually hot and long.
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Old 28th December 2011, 08:15 PM   #307
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That gets back to my original observation about the lack of distortion rise with lower frequency.
Very strange observation, SY!

Use one common emitter stage, with stiff voltage bias, no emitter degradation, no feedback, feed signal from zero volt source directly to the base, and measure what you get on collector. Then come back and let's talk about observations.

Proposed apparatus: opamp follower with output connected directly to the base of a common emitter stage. Bias applied to the input of the opamp follower.
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Old 28th December 2011, 08:17 PM   #308
SY is offline SY  United States
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Anatoliy, could you sketch out the circuit you propose? I *think* there's a fundamental problem with it, but it may just be my interpretation of what you're proposing.
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Old 28th December 2011, 08:23 PM   #309
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Quote:
Originally Posted by SY View Post
Anatoliy, could you sketch out the circuit you propose?
I can't. No convenient drawing software for Linux.

1. NPN transistor. Emotter to ground, resistor in collector.

2. Opamp. Output to inverting input (follower). Output of opamp directly to base of transistor.

3. Voltage divider, 1 resistor from + rail and one trimpot to ground. Whipper of the trimpot to the non-inverting input of the opamp.

4. Signal from signal generator to the non-inverting input of the opamp through coupling capacitor.

For measurement first set 1/2 of B+ on collector of the transistor adjusting trimpot.

Measure. Enjoy. The junction itself is the best indicator of it's temperature.

The fundamental problem is, how to tell which distortions are thermally induced on background of huge distortions of the stage itself.
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Last edited by Wavebourn; 28th December 2011 at 08:25 PM.
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Old 28th December 2011, 08:23 PM   #310
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That gets back to my original observation about the lack of distortion rise with lower frequency.
OK, but I'm still interested in brief signals that are 20dB or more greater than the average level.
Does running the output devices and drivers at room temperature or above the boiling point of water make any difference? How could you tell and how could you separate any difference found from other causes (PSU, or other)?
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