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Old 9th January 2010, 10:30 AM   #11
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Quote:
Originally Posted by akis View Post
I will now go and try on a couple of transistors, I will record the data and plot new real graphs, not simulated.
1000 transistors measure of the time of the model, make the average, comes to you exactly model. Measure one transistor and you can be sure that different from the model.

When you understand this, then you learn the models work better.
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Old 9th January 2010, 03:46 PM   #12
akis is offline akis  United Kingdom
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Here is the table of results. The hFE=126 is because the tranny must have got hot. I tried to be as quick as I could to reduce temperature problems but I had to look at two different meters and at 49mA across 23 volts it must have got hotter.

As you can see there is a very small increase of hFE with Vce but less than 1% over the range, whereas SPICE reports 50% !!!

If there is a transistor model that you trust please send it to me so I can test.

Code:
MJE15032
Vce	Ic (mA)	Vrb (mV)	hFE
22.8 V	1	11.8	84.75
	2.08	23.2	89.74
	5.19	54.3	95.58
	9.68	96.3	100.55
	49	387	126.61

3.9 V	1.1	13.2	83.33
	2.1	24	87.5
	5.05	55.1	91.65
	10.18	107.3	94.87
	43	426	100.94
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Old 22nd January 2010, 10:27 PM   #13
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I suppose the real question is whether it is possible, with the current model, to accurately model the Vce effects.

Why not try comparing a real MJL1302A specimen with Andy_C's models. Multiple, even, to see how far the parameters spread. And you might also see if turning Vaf down in the model will fix the issue.

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Old 23rd January 2010, 02:46 AM   #14
klewis is offline klewis  United States
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Hi,

I measured an mjl3281 today with the rig shown in the schematic.

The model is slightly optimistic compared to the actual tests. I was using aligator test leads, which may limit the current. So maybe tomorrow I'll rig it up with 18ga wires to see if it make a difference.

Here are the results.

With a setup as shown in the schematic, 33v rail.

For a 8 ohm load: 46ma of current at the base, 2.767A output. hFe 59Simulation says: across R2 - 29ma; across R1 - 3.286A output. hFe113


For a 3 ohm load, 47ma of current at the base, 5.304A output. hFe =112
Simulation says: across R2 - 57ma; across R1 - 6.861A output. hFe = 119

For a 1.5ohm load, 62ma of current at the base, 7.220A output. hFe = 116 Simulation says: across R2 - 82ma; across R1 - 10.344A. hfe = 126

My multimeter has a min, max hold function, I first put it between the R2 resistor and the base cycled on and off for 1/2 second or so. Then re rigged between the emitter and R1. Repeated the 1/2 second cycle. I think this helped keep the transistor from cooking.

Ken L
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File Type: png mjl3281 physical test schematic.png (10.1 KB, 227 views)
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Old 23rd January 2010, 03:15 PM   #15
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Here are all of Andy_C's models, which are supposed to be very accurate to the datasheet.

.MODEL mjl3281a_x npn IS=9.8145e-12 BF=438.0 NF=1.00 VAF=38 IKF=19.0 ISE=1.0e-12 NE=1.1237388682 BR=4.98985 NR=1.09511 VAR=4.32026 IKR=4.37516 ISC=3.25e-13 NC=3.96875 RB=3.997 RE=0.00 RC=0.06 XTB=0.115253 XTI=1.03146 EG=1.11986 CJE=1.144e-08 VJE=0.468574 MJE=0.34957 TF=2.6769e-9 XTF=7500 VTF=3.0 ITF=1000 CJC=1.093685e-9 VJC=0.623643 MJC=0.482111 XCJC=0.959922 FC=0.1 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1 Vceo=200 Icrating=15 mfg=OnSemiconductor
.MODEL mjl1302a_x pnp IS=9.8145e-12 BF=122.925 NF=1.00 VAF=40 IKF=19 ISE=9.18577762370362E-07 NE=5.0 BR=4.98985 NR=1.09511 VAR=4.32026 IKR=4.37516 ISC=3.25e-13 NC=3.96875 RB=3.30 RE=0.00 RC=0.06 XTB=0.115253 XTI=1.03146 EG=1.11986 CJE=1.561e-08 VJE=0.781803 MJE=0.433868 TF=3.257e-9 XTF=1000 VTF=2.0 ITF=260 CJC=2.346838e-9 VJC=0.27876 MJC=0.411324 XCJC=0.959922 FC=0.1 CJS=0 VJS=0.75 MJS=0.5 TR=1e-07 PTF=0 KF=0 AF=1 Vceo=200 Icrating=15 mfg=OnSemiconductor
.MODEL Q2SA1837_x PNP ( IS=2.39372559E-10 NF=1.304015937 BF=300 VAF=273 IKF=2.087725944 NK=0.94719458 ISE=1.46829699E-11 NE=1.526663542 BR=4 NR=1 VAR=20 IKR=1.05 RE=0 RB=1.8 RC=1.65 CJE=4.7407E-10 VJE=1.1 MJE=0.5 CJC=8.6700E-11 VJC=0.3 MJC=0.3 TF=1.642191E-09 FC=0.5 ITF=1.076260106 XTF=5.868994022 TR=1.38U)
.MODEL Q2SC4793_x NPN ( IS=1.8E-09 NF=1.43 BF=146.38 VAF=273 IKF=2.6 NK=0.95 ISE=6.286997E-10 NE=2.223629 BR=4 NR=1 VAR=20 IKR=1.05 RE=0 RB=1.7 RC=1.25 CJE=5.96964E-10 VJE=1.1 MJE=0.5 CJC=5.78E-11 VJC=0.3 MJC=0.3 TF=1.22678E-09 FC=0.5 ITF=10 XTF=99.52253015 TR=983N)

It may be easier to test the 2Sx models since they are lower current.

Klewis, maybe you have misunderstood. He is talking about Vce versus Beta. At higher voltages, beta is supposed to rise (regardless of current. The simulator models this, but apparently most models are not done well.)

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Old 23rd January 2010, 03:39 PM   #16
klewis is offline klewis  United States
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keantoken,

Yes I guess that I mis understood. What I was after was from an earlier question regarding hFe at higher voltages than the data sheet shows.

Ken
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Old 23rd January 2010, 03:46 PM   #17
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Well, these tests seem to show that neither data sheets OR models are reliable! We live in a confused world don't we?

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Old 23rd January 2010, 03:54 PM   #18
klewis is offline klewis  United States
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my measurements are within 10% or so, not too bad.
So how would I measure beta? The rig is still on the test bench. It's based on the schematic I posted.

Ken
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Old 23rd January 2010, 03:58 PM   #19
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Beta is Ic/Ib, so put a resistor in series with the collector to measure collector current.

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Old 24th January 2010, 07:38 PM   #20
akis is offline akis  United Kingdom
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Quote:
Originally Posted by klewis View Post
Hi,

I measured an mjl3281 today with the rig shown in the schematic.

The model is slightly optimistic compared to the actual tests. I was using aligator test leads, which may limit the current. So maybe tomorrow I'll rig it up with 18ga wires to see if it make a difference.

Here are the results.

With a setup as shown in the schematic, 33v rail.

For a 8 ohm load: 46ma of current at the base, 2.767A output. hFe 59Simulation says: across R2 - 29ma; across R1 - 3.286A output. hFe113


For a 3 ohm load, 47ma of current at the base, 5.304A output. hFe =112
Simulation says: across R2 - 57ma; across R1 - 6.861A output. hFe = 119

For a 1.5ohm load, 62ma of current at the base, 7.220A output. hFe = 116 Simulation says: across R2 - 82ma; across R1 - 10.344A. hfe = 126

My multimeter has a min, max hold function, I first put it between the R2 resistor and the base cycled on and off for 1/2 second or so. Then re rigged between the emitter and R1. Repeated the 1/2 second cycle. I think this helped keep the transistor from cooking.

Ken L
It's great doing real experiments on real circuits. Although I would not bother with 10A, after all my bench supply only goes up to 2A, but in any case there are significant deviations from the "truth" with small transistors and small currents, eg 0.5mA-10mA, first we need to try and find out what the heck is happening.

Also, hFE is severely affected by temperature, you can put your index finger on a small signal transistor and the hFE will jump by 10. A medium power transistor getting hot to the touch has seriously different hFE than when at room temperature, so all measurements are best done with 2 multimeters and even then it is hard to keep constant temperatures.
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