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Old 25th March 2010, 12:09 PM   #971
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Quote:
Originally Posted by keantoken View Post
On the conversation about transistor testing:

With some work, I'm sure we could come up with a circuit designed to keep a transistor at constant dissipation/temperature while ramping up whichever parameters we're testing.

So say we want to extract an Hfe vs. Ic curve for a given device. We want to keep the device at a constant temperature so we decide to keep the dissipation at a steady 10W. Vce for the test will be 10V.

Average Ic for this would be 1A. So if we send the test current in pulses, with a duty cycle varying so as to keep an average of 1A, we will keep an average dissipation of 10W. The higher the frequency the better.

Duty cycle=Iavg/Itest

Are there any outstanding issues with this approach? The device should probably be left for a warm up period so temperature can stabilize.

- keantoken
actually not so difficult as it seems. using voltage controlled current sources and some stepped voltage sources, a curve tracer is a piece of cake. temperature control can be done with a large heat sink in a water bath (nor a perfect solution, but it would work better than a free standing transistor). temperature sensing can be done from the device Vbe. if the initial Vbe at 25C is known for a device, then the die temp for that device can be calculated from the Vbe following the -2.2mV/C characteristic of silicon. if the tracer were a PC controlled device, the Vbe could be sensed as part of the programmed tracing routine during an idle state between traces. the voltage/current data could be fed to a set of ADC,s and the curve data digitized, simplifying the modeling process. the software would be more difficult to make than the hardware. even without all of the data acquisition hardware, a simple curve tracer can be made with current sources, stepped voltage sources and an oscope. somewhere in my "archives" i have the schematic for one using CMOS counters for the stepped voltage sources that control the current sources.
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Old 25th March 2010, 11:25 PM   #972
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I suppose Vbe temperature sensing would be done on the "off" half of the duty cycle.

Maybe, in fact, the temperature sensing could be used as a form of negative feedback to control the switching.

- keantoken
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Old 28th September 2010, 12:39 PM   #973
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Default LME49710 model

Quote:
Originally Posted by syn08 View Post
Not sure if this is not already old news: National released the spice model for their high performance audio opamps (LM4562, LME49710, LME49720, and LME49740)

http://www.national.com/models/spice/LM/LME49860.zip

The model seem to be pretty accurate.
This model is intended for dual versions of above series of op-amps.
For single versions, like the LME49710, the supply current is way too high: 10mA, instead of 4.8mA (typically).
Regrettably, NS didn't publish a model for the latter, but one can easily modify the LME49860 model in order to get the correct supply currents. Go to the 93rd line and replace the current source "I9 8 4 5.8E-3" by "I9 8 4 0.66E-3". See also pic below.

Cheers,
E.
Attached Images
File Type: png LME49710mod.png (2.6 KB, 266 views)
__________________
Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
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Old 5th February 2011, 04:44 PM   #974
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Default Simulation Problems

I'm trying to simulate a very simple power amp and am getting bogus results. I've got the actual circuit working, but when I plug in the values I used, the output is driven to the negative rail.

I've tried this with Falstad's circuit simulator and SIMetrix with similar results.

I've checked and checked my schematic capture and it is like the amp I built. Unfortunately, the simulator thinks the circuit doesn't work.

It's my first time with a simulator and need some help. The Falstad circuit simulator is quick, easy and very cool. But the output is suspect. Because I get similar results with two simulators, I'm thinking it might be me.

Is this the right thread to ask for help?
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Old 5th February 2011, 04:59 PM   #975
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Post your schematic or whatever and I will take a look.

- keantoken
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Old 5th February 2011, 05:39 PM   #976
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Default Circuit

Thanks for your offer to help. Here is the picture:

SOCheap150.png

The following is the net list exported from the Falstad simulator. You can run the Java applet at falsted.com. To import you would just paste the following into the import window in Falsted.

Code:
$ 0 4.9999999999999996E-6 10.634267539816555 43 2.0 50
t 1008 224 1040 224 0 1 -47.86079739748146 0.8552854219172727 100.0
t 512 480 544 480 0 1 -52.69926583344467 -0.253812085630301 100.0
t 864 192 896 192 0 1 -47.12089238070345 0.7399050167780139 100.0
t 1008 528 1040 528 0 -1 0.9955962439225914 -0.8571644056443688 100.0
t 864 560 896 560 0 -1 0.2538120759022249 -0.7417841680203665 100.0
t 272 304 304 304 0 -1 50.50652531151723 8.352876252693331 100.0
t 368 304 336 304 0 -1 41.553834077834395 -0.5998149712614245 100.0
r 1040 304 1040 352 0 0.33
r 1040 432 1040 384 0 0.33
r 976 272 1024 272 0 150000.0
r 976 480 1024 480 0 150000.0
r 528 176 480 176 0 3300.0
r 448 176 400 176 0 3300.0
r 336 192 336 240 0 22000.0
r 304 544 304 608 0 1600.0
r 256 320 256 384 0 22000.0
r 384 320 384 368 0 470.0
r 400 304 464 304 0 22000.0
r 544 512 544 576 0 33.0
r 128 304 176 304 0 2200.0
c 208 304 240 304 0 1.0E-5 -0.05888382426463867
c 192 320 192 368 0 1.0E-10 0.4476414775245122
c 464 208 464 272 0 1.0E-5 48.94284784685432
g 256 464 256 480 0
g 1120 432 1120 480 0
r 1120 384 1120 432 0 4.0
R 1040 608 1040 640 0 0 40.0 -50.0 0.0 0.0 0.5
R 1040 144 1040 112 0 0 40.0 50.0 0.0 0.0 0.5
g 384 432 384 448 0
w 112 304 128 304 0
w 192 368 192 384 0
w 192 384 256 384 0
w 256 384 256 464 0
c 384 384 384 416 0 9.999999999999999E-5 -8.158090260387986
w 384 320 384 304 0
w 384 304 400 304 0
w 368 304 384 304 0
w 304 320 304 544 0
w 384 368 384 384 0
w 384 416 384 432 0
w 336 320 336 608 0
w 336 608 304 608 0
c 464 512 496 512 0 1.0E-5 -0.253812085630301
d 544 224 544 256 1 0.805904783
d 544 272 544 304 1 0.805904783
d 544 416 544 448 1 0.805904783
w 496 512 544 512 0
w 544 496 544 512 0
w 512 480 448 480 0
w 448 480 448 512 0
w 448 512 464 512 0
w 304 288 304 256 0
w 464 272 464 304 0
w 544 384 544 416 0
w 544 448 544 464 0
w 544 576 544 608 0
w 544 608 336 608 0
w 448 512 304 512 0
w 304 512 304 544 0
w 528 176 544 176 0
w 544 176 544 224 0
w 1040 208 1040 144 0
w 896 176 896 144 0
w 896 208 896 224 0
w 1040 352 1040 384 0
w 1040 544 1040 608 0
w 896 576 896 608 0
w 896 544 896 528 0
w 1120 384 1120 368 0
w 1120 368 1040 368 0
w 1040 368 1040 352 0
r 864 224 864 256 0 10000.0
r 864 496 864 528 0 10000.0
w 832 176 832 192 0
w 832 192 864 192 0
w 864 192 864 224 0
w 864 256 864 272 0
w 864 480 864 496 0
w 864 528 864 560 0
w 544 512 576 512 0
w 544 256 544 272 0
w 1040 368 544 368 0
w 464 368 464 304 0
w 576 512 608 512 0
w 608 560 864 560 0
v 112 304 112 464 0 1 100.0 1.0 0.0 0.0 0.5
w 112 464 256 464 0
w 464 368 544 368 0
w 544 304 544 384 0
w 544 176 832 176 0
w 1040 432 1040 480 0
w 1024 480 1040 480 0
w 1040 480 1040 512 0
w 864 480 928 480 0
w 976 480 928 480 0
w 928 480 928 528 0
w 896 528 928 528 0
w 1008 528 928 528 0
w 608 512 608 560 0
w 1040 240 1040 272 0
w 1024 272 1040 272 0
w 1040 272 1040 304 0
w 864 272 928 272 0
w 928 272 928 224 0
w 928 272 976 272 0
w 896 224 928 224 0
w 1008 224 928 224 0
w 336 144 896 144 0
w 896 144 1040 144 0
w 544 608 896 608 0
w 1040 608 896 608 0
w 176 304 192 304 0
w 192 304 192 320 0
w 192 304 208 304 0
w 240 304 256 304 0
w 256 304 256 320 0
w 256 304 272 304 0
w 304 256 336 256 0
w 336 240 336 256 0
w 336 256 336 288 0
w 336 144 336 176 0
w 336 176 336 192 0
w 336 176 400 176 0
w 448 176 464 176 0
w 464 176 464 208 0
w 464 176 480 176 0
o 69 64 0 35 80.0 12.8 0 -1
o 57 64 0 35 80.0 9.765625E-5 1 -1
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Old 5th February 2011, 05:52 PM   #977
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It looks like the schematic is drawn wrong. You circuit is a jumble of at least 3 different topologies in a way that can't possibly work. Why don't you post your inspiration for the circuit, or find a proven schematic online to work with?

LTSpice is what I use, and it has an Education folder with a simple power amp example.

- keantoken
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Old 5th February 2011, 06:00 PM   #978
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Here is that example I was talking about. I wouldn't build it for myself, but it will get you started.

- keantoken
Attached Images
File Type: png SimpleAudioAmp.png (120.5 KB, 141 views)
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Old 5th February 2011, 06:26 PM   #979
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Default Original Inspiration

Here is the original inspiration...

cheap150.jpg

Here's another one very much like it...

100W Amp.jpg

In my schematic, I simply made the TIP142/147 darlingtons into discrete pairs. That was after I tried single transistors with very high hfe. That didn't work either.

Yeah, I might have drawn the schematic wrong, but I can't find the error.

I'll try LTSpice again. I installed it but stopped working with it because I don't get the user interface. I entered the schematic, but can't figure out how to get steady state plots in Volts for a transient analysis.

Here's my LTSpice schematic. This is just a text file saved from the original ASC file. If you save it as an .asc file, LTSpice will open it.

SOCheap150.txt
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Old 5th February 2011, 07:01 PM   #980
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I found one small problem in the Falstad circuit. It's the 10uF cap between base and emitter of the driver. It should be a 100pF between base and collector. It doesn't make much difference in the simulation. Here's the corrected circuit:

Code:
$ 0 4.9999999999999996E-6 10.634267539816555 43 2.0 50
t 1008 208 1040 208 0 1 -48.73317764062409 0.8548069035323701 100.0
t 512 464 544 464 0 1 -51.00419236198607 -0.24972226768478123 100.0
t 864 176 896 176 0 1 -47.99375118686806 0.7394264537560336 100.0
t 1008 512 1040 512 0 -1 0.9911076442171307 -0.8567554972692548 100.0
t 864 544 896 544 0 -1 0.24973241999998663 -0.7413752242171441 100.0
t 272 288 304 288 0 -1 57.6209433924192 12.992524366523424 100.0
t 368 288 336 288 0 -1 44.02970730879695 -0.5987218694140273 100.0
r 1040 288 1040 336 0 0.33
r 1040 416 1040 368 0 0.33
r 976 256 1024 256 0 150000.0
r 976 464 1024 464 0 150000.0
r 528 160 480 160 0 3300.0
r 448 160 400 160 0 3300.0
r 336 176 336 224 0 22000.0
r 304 528 304 592 0 1600.0
r 256 304 256 368 0 22000.0
r 384 304 384 352 0 470.0
r 400 288 464 288 0 22000.0
r 544 496 544 560 0 33.0
r 128 288 176 288 0 2200.0
c 208 288 240 288 0 1.0E-5 -0.20227512325988162
c 192 304 192 352 0 1.0E-10 7.418678421474524
c 464 192 464 256 0 1.0E-5 48.04869136644873
g 256 448 256 464 0
g 1120 416 1120 464 0
r 1120 368 1120 416 0 4.0
R 1040 592 1040 624 0 0 40.0 -50.0 0.0 0.0 0.5
R 1040 128 1040 96 0 0 40.0 50.0 0.0 0.0 0.5
g 384 416 384 432 0
w 112 288 128 288 0
w 192 352 192 368 0
w 192 368 256 368 0
w 256 368 256 448 0
c 384 368 384 400 0 9.999999999999999E-5 -5.619807378713874
w 384 304 384 288 0
w 384 288 400 288 0
w 368 288 384 288 0
w 384 352 384 368 0
w 384 400 384 416 0
w 336 304 336 592 0
w 336 592 304 592 0
d 544 208 544 240 1 0.805904783
d 544 256 544 288 1 0.805904783
d 544 400 544 432 1 0.805904783
w 544 480 544 496 0
w 512 464 448 464 0
w 448 464 448 496 0
w 304 272 304 240 0
w 464 256 464 288 0
w 544 368 544 400 0
w 544 432 544 448 0
w 544 560 544 592 0
w 544 592 336 592 0
w 528 160 544 160 0
w 544 160 544 208 0
w 1040 192 1040 128 0
w 896 160 896 128 0
w 896 192 896 208 0
w 1040 336 1040 368 0
w 1040 528 1040 592 0
w 896 560 896 592 0
w 896 528 896 512 0
w 1120 368 1120 352 0
w 1120 352 1040 352 0
w 1040 352 1040 336 0
r 864 208 864 240 0 10000.0
r 864 480 864 512 0 10000.0
w 832 160 832 176 0
w 832 176 864 176 0
w 864 176 864 208 0
w 864 240 864 256 0
w 864 464 864 480 0
w 864 512 864 544 0
w 544 496 576 496 0
w 544 240 544 256 0
w 1040 352 544 352 0
w 464 352 464 288 0
w 576 496 608 496 0
w 608 544 864 544 0
v 112 288 112 448 0 1 100.0 10.0 0.0 0.0 0.5
w 112 448 256 448 0
w 464 352 544 352 0
w 544 288 544 368 0
w 544 160 832 160 0
w 1040 416 1040 464 0
w 1024 464 1040 464 0
w 1040 464 1040 496 0
w 864 464 928 464 0
w 976 464 928 464 0
w 928 464 928 512 0
w 896 512 928 512 0
w 1008 512 928 512 0
w 608 496 608 544 0
w 1040 224 1040 256 0
w 1024 256 1040 256 0
w 1040 256 1040 288 0
w 864 256 928 256 0
w 928 256 928 208 0
w 928 256 976 256 0
w 896 208 928 208 0
w 1008 208 928 208 0
w 336 128 896 128 0
w 896 128 1040 128 0
w 544 592 896 592 0
w 1040 592 896 592 0
w 176 288 192 288 0
w 192 288 192 304 0
w 192 288 208 288 0
w 240 288 256 288 0
w 256 288 256 304 0
w 256 288 272 288 0
w 304 240 336 240 0
w 336 224 336 240 0
w 336 240 336 272 0
w 336 128 336 160 0
w 336 160 336 176 0
w 336 160 400 160 0
w 448 160 464 160 0
w 464 160 464 192 0
w 464 160 480 160 0
w 448 496 304 496 0
w 304 528 304 496 0
w 304 304 304 496 0
c 480 432 512 432 0 1.0E-10 -51.00419236198607
w 512 432 544 432 0
w 480 432 448 432 0
w 448 432 448 464 0
o 63 64 0 35 80.0 12.8 0 -1
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