Matching is usually most useful if carried out at the quiescent operating current.
If you can get a match over a range of currents that spreads either side of that quiescent value then even better.
If you can get a match over a range of currents that spreads either side of that quiescent value then even better.
Another thing I was thinking was adding either a thermistor or RTD to the emitter resistor for temperature compensation.
What say you to this idea?
What say you to this idea?
I presume you mean adding this in the application, not for testing.
What is your application? I don't think you said. That might have some bearing here...
Right now I'm just trying to get an accurate and consistent test. Over the course of the day I have been watching the Vbe on just one transistor. One of the things that prevents an accurate measurement is the power supply. I need a better voltage source that won't drift.
Also, even though the thermostat in the house has not changed, maybe the temperature in the room containing the test has changed. I'll have to monitor that closely too, which is the reason for some kind of temperature compensation.
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Thanks Mooly for this. Since I don't use Smilies, I will go and disable them permanently.
Just checked by going to "Go Advanced" and I see that the "Disable smilies in text" is already unticked.
My next post68, even with "Disable smilies in text" unticked is still converting the colon followed by the capital D as a smilie.
I have asked the Moderators the same in the past. Did they just ignore that previous request?
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It is nearly impossible for us amateurs to control Tj.
That is why I rely very much on compare.
I compare Ref😀ut when that type of accuracy is required. Absolute accuracy is beyond my resources.
I suggest you do similar.
For the current post:
Now I understand.
But does the other screen (Message Editor Interface) for wisiwig apply as a permanent "no smilies"?
Testing:
compare = REF😀UT
And it remembers for editing THIS post and retains the instruction to disable smilies.
Now I understand.
But does the other screen (Message Editor Interface) for wisiwig apply as a permanent "no smilies"?
Testing:
compare = REF😀UT
And it remembers for editing THIS post and retains the instruction to disable smilies.
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WYSIWYG (what you see is what you get) just displays your post (as you type and set it up) more true to how it will actually appear. It doesn't affect how the smilies appear in the final post but it give more options.
For example if I highlight this as bold you see it happen in real time and not highlight this as bold/as in the other more basic editors.
For example if I highlight this as bold you see it happen in real time and not highlight this as bold/as in the other more basic editors.
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If I want to retain bold and italics, then I have to keep wisiwig/WYSIWYG. Is that correct?
Does that mean that when I see an auto smilie corrupting my post I have to remember to Go Advanced and switch off the default smilie?
Does that mean that when I see an auto smilie corrupting my post I have to remember to Go Advanced and switch off the default smilie?
You don't need keep WYSIWYG. Not keeping it means you see the vbulletin code for things like colour or bold and so on. If I hadn't WYSIWG turned on I would not have seen that bold text until the message was posted. I would have seen the code for bold wrapped around the text as you see in the picture.
If you post a smilie by mistake you will have to edit the post and tick the smilies box. Check the basic text is as you want and then resubmit the post.
If you post a smilie by mistake you will have to edit the post and tick the smilies box. Check the basic text is as you want and then resubmit the post.
This looks like the solution I will have to adopt whenever I see a corrupted post due to a default autosomething overwriting what I thought I was posting.
Is there a way to correct the default insertion of ***** when the Forum software thinks we are typing "unapproved" words?
No problem. In fact its only through playing around with various settings and options that we learn. There is no user manual anywhere.
Ok, someone please explain this to me:
If you take a NPN BJT and hook the collector to +Vcc, the base to ground and the emitter to -Vcc via a resistor, what causes any current to flow through the base?
The base is not biased but I performed this test on a breadboard and current flowed through the collector and emitter but I could not detect any flowing through the base with my 5 1/2 digit meter.
If you take a NPN BJT and hook the collector to +Vcc, the base to ground and the emitter to -Vcc via a resistor, what causes any current to flow through the base?
The base is not biased but I performed this test on a breadboard and current flowed through the collector and emitter but I could not detect any flowing through the base with my 5 1/2 digit meter.
But the base is biased relative to the emitter. If the supplies are say -/+10 volts and your emitter resistor say 1k then around 30 microamps (give or take, it depends on the current gain of the transistor) will flow from ground into the base/emitter junction.
The base current will be there, your meter should show it but it needs to be set for a low current range. You could add a series resistor to the base and try measuring the volt drop across that to deduce the current.
Look at the simulation of what you describe. The -43uV reading relates directly to -43 microampsflowing in the 1 ohm resistor. There is around 9.3 milliamps in the emitter resistor. Ignoring the base current (because its so small) we get a forward gain of 9.3E-3/43E-6 which is 216. That's about right for a small signal transistor like the 2N2222
Edit... ground is just an arbitrary point you decide upon. Move the ground to the lower rail and it might be easier to visualise. Doing that gives you a 10 volt supply as 'bias'. The currents are identical if you calculate them out from the voltages and resistor values.
The base current will be there, your meter should show it but it needs to be set for a low current range. You could add a series resistor to the base and try measuring the volt drop across that to deduce the current.
Look at the simulation of what you describe. The -43uV reading relates directly to -43 microampsflowing in the 1 ohm resistor. There is around 9.3 milliamps in the emitter resistor. Ignoring the base current (because its so small) we get a forward gain of 9.3E-3/43E-6 which is 216. That's about right for a small signal transistor like the 2N2222
Edit... ground is just an arbitrary point you decide upon. Move the ground to the lower rail and it might be easier to visualise. Doing that gives you a 10 volt supply as 'bias'. The currents are identical if you calculate them out from the voltages and resistor values.
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