Testing the TK Tar Baby

[poynt99]

.99

Your analyze is not in agreement with actual measurements. Both TK and me got 0,09 Ampere bias current.
You also have just added the bias current to the main current. This is not correct and measurement shows
that this is not correct. Without the bias current running (removing the Q2) the overall circuit current is 1,92 Amp.
With the Q2 installed then the bias current is 90mA. But the overall current did drop to 1,78 Amp. Did you you Spice
simulator to get those numbers?

GL.

All indicated current and voltages were derived from a SPICE simulation on the NERD circuit with a 24 Volt supply, vs. 72V. I applied no math myself.

It would be impossible to correctly measure any significant DC current into the Gate of a working MOSFET. The current through the bias supply is NOT an indication of Gate current.

[Groundloop]

All indicated current and voltages were derived from a SPICE simulation on the NERD circuit with a 24 Volt supply, vs. 72V. I applied no math myself.

It would be impossible to correctly measure any significant DC current into the Gate of a working MOSFET. The current through the bias supply is NOT an indication of Gate current.

.99

We are talking pass each other. What I did address was that your simulation just did add the main current in the circuit
from the main input voltage source with the bias current in the bias loop. This is not what I see in measurement. When the
bias current is running through the MOSFET at the same time as the main current is running through the MOSFET we get
an reduction of the main current. And this reduction is not (main current - bias current). If you remove the bias current by removing
the other MOSFET the the main current is approx. 1,94 Amp. Insert the other MOSFET and the main current drops to 1,74 Amp.
I can't get the numbers correct even if the bias current was 113mA. 1,74 + 0,113 = 1,853 Amp. Do you see what I mean?

GL.

[poynt99]

If you remove the bias current by removing the other MOSFET the the main current is approx. 1,94 Amp. Insert the other MOSFET and the main current drops to 1,74 Amp.
I can't get the numbers correct even if the bias current was 113mA. 1,74 + 0,113 = 1,853 Amp. Do you see what I mean?

GL.

I think I see what you mean, but to be sure could you label my diagram with your measurements? Also, if you could indicate where you are taking your current measurements (i.e. where is your current meter inserted for each measurement?). Thanks.

[poynt99]

It is important to distinguish where the measurements are being taken, because it varies depending where. For eg.

Q1 Source current:
1.67A with Q2 installed, 1.6A with Q2 pulled (a decrease in current)

Load current:
1.52A with Q2 installed, 1.6A with Q2 pulled (an increase in current)

[Groundloop]

I think I see what you mean, but to be sure could you label my diagram with your measurements? Also, if you could indicate where you are taking your current measurements (i.e. where is your current meter inserted for each measurement?). Thanks.

.99

Here is what I'm measuring.

GL.