That is poor advise and borders on the intemperate. The iPad brings me considerable advantages and I shall continue to use it whenever possible - including DIYA. I have already said I will use the PC if I need to post .asc files so your advice is also irrelevant. Why so aggressive ?
Why so aggressive ?
Because many of us are here trying to slow the inexorable advance of unnecessary, unwanted technology. Because anything with a prefix "i" or a silly name like "tapatalk" is anathema. I for example still prefer analogue and regret the passing of OS2. (I have had to buy a CD player but its a mid 80's Marantz that I have restored and that makes it acceptable)
Now, none of this is your problem of course and I hope you're not offended. But I did have a nice chuckle thanks to the exchange.
With regard to your attachment problem, I have no idea how to help. Sorry.
Because many of us are here trying to slow the inexorable advance of unnecessary, unwanted technology. Because anything with a prefix "i" or a silly name like "tapatalk" is anathema. I for example still prefer analogue and regret the passing of OS2. (I have had to buy a CD player but its a mid 80's Marantz that I have restored and that makes it acceptable)
Now, none of this is your problem of course and I hope you're not offended. But I did have a nice chuckle thanks to the exchange.
With regard to your attachment problem, I have no idea how to help. Sorry.
You are talking to a fellow traveler Johno, I’m still mourning the demise of DOS (forgotten but not gone?) and, while I despise Windows, I do have a very high regard for intel’s ‘86.
Glad you had a nice chuckle and why not? I do wish we could get back to subject though.
O.K. Andrew, I'm now on the PC, please do bear with me as I post a .asc:
Oh, that's much better. Would you be so kind as to run this for me and let me know if I've got it right?
You should see a Dual Moog Vbe tester. Change Temp or mismatch UUTs (A,B,C suffix) to explore the circuit.
Thank you.
I see a pic with all the components pulled from the LTspice libraries.
I am not an LTspice user and have never managed to remember enough to properly use the simulator as a tool.
What does the Vbe tester do?
I can see the resistor ladder is sending 5Vdc (50% of the supply voltage) to the two +IN pins. Opamps do all they can to make the -IN pins match the same voltage.
That makes the output pin of each opamp one Vbe below 5Vdc, i.e. ~ 4.4Vdc + the error due to finite gain of the opamp and the error due to output offset. Note the two upper BJTs will have a different Vbe. That means the two outputs will settle to a different output voltage value and then the two errors will be different between the two similar halves.
You will have quite different settings the the two halves.
How does that "test" the two BC devices? Which is it testing, the upper, or the lower?
I am not an LTspice user and have never managed to remember enough to properly use the simulator as a tool.
What does the Vbe tester do?
I can see the resistor ladder is sending 5Vdc (50% of the supply voltage) to the two +IN pins. Opamps do all they can to make the -IN pins match the same voltage.
That makes the output pin of each opamp one Vbe below 5Vdc, i.e. ~ 4.4Vdc + the error due to finite gain of the opamp and the error due to output offset. Note the two upper BJTs will have a different Vbe. That means the two outputs will settle to a different output voltage value and then the two errors will be different between the two similar halves.
You will have quite different settings the the two halves.
How does that "test" the two BC devices? Which is it testing, the upper, or the lower?
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If you can see the circuit, Andrew, you must be in LtSpice.
Just click the running man (toolbar left), dismiss the operating point popup and it will show UUT1(2) Vbe to be 554.95mV (currently showing ???).
U1/Q1 is just a current source for UUT1 (ditto U2/Q2/UUT2).
Edit .Temp27 to .Temp40 say, run it again and the Vbe's change to 527mV with temperature. Edit UUT1 to an A or C variant, causing a mismatch, and note the delta Vbe.
It tests UUT1/2 - the units under test.
This is 'Synthesiser' Moog's circuit BTW, so please don't shoot the piano player, I have a much better tester that doesn't change with temperature. Here I'm just posting a .asc - yes?
And thank you - it works fine.
The upper transistor choice won't alter the currents flowing in the devices under test because the opamp will compensate for whatever difference in characteristic there may be in the upper transistor.
You can even add another diode volt drop to either upper device and nothing changes for the two under test.
You can even add another diode volt drop to either upper device and nothing changes for the two under test.
Thanks for jumping in.
It made me think again and see that the Emitter voltage of both upper BJTs are at the same voltages as the -IN nodes. i.e. the volts drop across the 51k is the same, plus or minus the tiny errors generated by the differences in finite gain and output offset.
So I take back what I said in post 31.
It made me think again and see that the Emitter voltage of both upper BJTs are at the same voltages as the -IN nodes. i.e. the volts drop across the 51k is the same, plus or minus the tiny errors generated by the differences in finite gain and output offset.
So I take back what I said in post 31.
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Some think it should have 10k R5. Reduces UUT dissipation, cool it down maybe?
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Ok Mooly, thanks for that. I think Its time I posted my own Vbe matcher - it’s a lot simpler.
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