Claimed OU circuit of Rosemary Ainslie

[MileHigh]

P.S.:  Now I have switched over to the fisrt graph in Glen's posting #2893.  it shows a discontinuity in the current waveform that wasn't apparent in the other graph.  I am seeing more now and am still in contemplation.  The big revelation is that it is only a half sine wave after the MOSFET switches off.

I am now shaky for explaining the exact mechanism for the reverse current but the wheels are turning.  More tomorrow.

MileHigh

[Rosemary Ainslie]

P.S.:  Now I have switched over to the fisrt graph in Glen's posting #2893.  it shows a discontinuity in the current waveform that wasn't apparent in the other graph.  I am seeing more now and am still in contemplation.  The big revelation is that it is only a half sine wave after the MOSFET switches off.

I am now shaky for explaining the exact mechanism for the reverse current but the wheels are turning.  More tomorrow.

MileHigh

Can't wait.  I'm happy with all these questions.  More later.

[Rosemary Ainslie]

Hi MileHigh.  I take it that my little lapse into lecture mode did not wash that well.  I tend to excess.  It's my only fault.   

I'm looking forward to giving my own interpretation of the waveform.  Diametrically opposed to mainstream.  But I'll wait and see if Fuzzy or someone ever manages a clear gain in COP.

Regarding the invincible trio of Rodin, Buturff and Harieman - we've now got Buturff as a fully qualified member at the forum.  Am hoping for answers to many, many questions. 

ROSIE ? 

edit.  You play bridge?  What convention? 

[Hoppy]

MH,

I agree with some of your analysis, however I have another explanation for the negative spike, post Gate-OFF.

First off, I did not read Harvey's post, but after you mentioned it, I took a look. He's not even close to the mark with his induction theory. In fact he mentions then all together dismisses the correct answer.

Here's what's causing that negative pulse on the shunt that is coincident with the positive inductive spike on the Drain:

When the MOSFET finally does switch OFF (it is a slow one indeed), the Drain voltage spikes positive relative to ground, but the inductor energizing current not only begins decreasing, it eventually passes through 0 Amps and begins increasing in the negative or opposite direction. It is this current inversion in concert with the positive voltage spike that creates this negative spike, and all the subsequent negative excursions on the shunt during ringdown.

I am confident this can be experimentally verified with the present setup.

.99

Poynt99

IMO this is the correct explanation. The discharge from the inductive element of the load is a reverse current through the mosfet body diode and shunt. We see a rise in drain potential coupled with a negative going current. As MH says, there should be an instant of time where a potential difference does not exist across the load at the point immediately prior to the inductor discharging in the opposite direction to which it was charged. If a 'freewheel' diode were to placed across the load then the inductor discharge would be in the same direction as the direction of its charging current and no negative excursions would be seen on the shunt waveform.

Hoppy

[hoptoad]

Poynt99

IMO this is the correct explanation. The discharge from the inductive element of the load is a reverse current through the mosfet body diode and shunt. We see a rise in drain potential coupled with a negative going current. As MH says, there should be an instant of time where a potential difference does not exist across the load at the point immediately prior to the inductor discharging in the opposite direction to which it was charged. If a 'freewheel' diode were to placed across the load then the inductor discharge would be in the same direction as the direction of its charging current and no negative excursions would be seen on the shunt waveform.

Hoppy

Yep, sounds right. A "freewheel" diode across the load in opposite polarity to the coil supply will create a unidirectional circulation path for the current produced by the collapsing field of the coil during off mode.

It will change the waveform and should introduce a longer dissipation rundown time on the coil's current and its magnetic field.. That is, it will cause the 'on' portion of the duty cycle of the coil to be longer than the actual signal switching 'on' portion of the duty cycle.

cheers