Testing the TK Tar Baby

[TinselKoala]

.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.

I want to stress that the bias current I measured STARTED at 90 mA, quite consistently, but always quickly rose to 130-150 mA. I thought this was weird so I tried this with all the IRFPG50s that I have (except ironically the known bad one, I now realize), even two unused ones, and they all showed about the same behaviour, some faster some slower to rise up to the higher current.
So I'm wondering if this is just a characteristic of the particular mosfet (GL has the IRFPF50, I think) or what. How long did GL keep the measurment going? For me, in 5 or ten seconds the current started to rise from 90 heading up.

[Groundloop]

Poynty that diagram of yours is not right.  Your reference to that 'Q2' MOSFET shows the bias supply in series with the main supply.  Which is correct.  As is your Q1 MOSFET reference where you show the bias supply is in parallel to the main supply.  Here's where you 'error'.

. The body diode of your reference Q1 is NOT connected to the supply source or to the circuit's negative drain rail.
. It is ONLY connected to the terminal of the function generator's probe.
. It is floating - together with the your referenced Q1 Source.
. Therefore it CANNOT conduct current from the battery supply source -
. Even if that battery supply exceeded that diode's 'zener knee' voltage level

If you want to argue that the battery supply source can discharge current through your referenced Q1 you'll have to argue it against it's actual connections.

Regards,
Rosie

And may I add - IF that diode could conduct current from the battery supply while the bias supply is in parallel - then even more reason to suppose that it would do so while the bias supply were in series with the battery supply source.  In which case there would be a continual battery discharge and the MOSFETs would NOT switch.

Rosemary,

.99 got the drawing correct. But my measurements does not agree with the numbers he got.
The Q2 body diode is in series with the function generator positive pulse input and is conducting
0,09 Ampere of current. The voltage drop over the diode is 1,8 Volt. The bias current going
through the Q1 MOSFET is effecting the overall current and is reducing the current.
You are correct in saying that the Q2 body diode can not conduct current from the main input battery.
The Q2 body diode is ONLY conducting current from the BIAS voltage input from the function generator.

GL.

[MileHigh]

TK:

It's possible that what you are observing is the heating up of the quasi-junction inside the MOSFET.  Higher temp equals higher current transfer through a MOSFET, correct?

Assume that when the current is bleeding through the zener diode, that a fairly small volume inside the MOSFET represents the actual junction.  So it becomes a kind of pin-point "hot reactor core" and it takes a while for the thermal equilibrium to take place.

MileHigh

[TinselKoala]

TK you are not only as wrong as ever and hopelessly OFF TOPIC but you're getting WAY too boring.  CONCENTRATE on Groundloops posts.  They - at LEAST - could teach you something. 

Rosie Pose

Quite apart from the general vulgarity of your rather 'dismal' invective - is that video - 'making out with a dog' boomp - boomp boomp.  That should have been censored - LONG back - IN ITS ENTIRETY.  And that's not even touching on your 'gross' vulgarity in 'name calling' that you seem to think is clever and simply parades your infantile emotional level of maturity.

Rosie Pose

You are definitely the most astounding hypocrite I have ever met, outside of politics.

YOU need to pay close attention to Groundloop's excellent work. More than that YOU need to pay attention to HOW he does it and HOW he accomplishes what he does. In addition, you should note that he has the integrity to examine his misunderstandings CAREFULLY and PROPERLY and to correct them when he discovers his errors.
He engaged in a textbook dimensional analysis that, once again, Proved You Wrong about your ridiculous ideas about power and energy and their unit definitions and usages.

PAY ATTENTION TO GROUNDLOOP, Polly Parrot. He is setting an example that you must learn to emulate if you really want to swim with the sharks of scientific publishing.

[Rosemary Ainslie]

Rosemary,

.99 got the drawing correct.

Not so sure about this.  I'll check this out again and get back here. 

But my measurements does not agree with the numbers he got.
The Q2 body diode is in series with the function generator positive pulse input and is conducting
0,09 Ampere of current. The voltage drop over the diode is 1,8 Volt. The bias current going
through the Q1 MOSFET is effecting the overall current and is reducing the current.
You are correct in saying that the Q2 body diode can not conduct current from the main input battery.
The Q2 body diode is ONLY conducting current from the BIAS voltage input from the function generator.

GL.

Groundloop I can't argue this.  You're dealing with the data from your experiment.  I'll sit tight and see where this argument goes.

Kindest as ever,
Rosie

ADDED
I've just checked.  Sadly - Poynty's not with us at the moment.  I'll wait for his answer to you Groundloop.

as ever,
R