Rosemary Ainslie circuit demonstration on Saturday March 12th 2011

[neptune]

@poynt99 .Re the graph on the Wicki page you provided a link to . What I find hard to understand is this . The vertical scale on the graph shows drain current . But the higher numbers are at the bottom of the scale and the lower numbers are at the top . From this , I would deduce that the higher the voltage on the gate , the Lower the Drain current .This can not be true in the case of the type of Mosfet we are talking about . What have I missed and what is the significance of the letter "E" in the Drain current numbers . I think what you may be trying to say is that some current can flow between drain and source with zero gate voltage ? The animation however appears to show that about0.5 volts  is  needed on the gate  to permit any drain-source current to flow .

[poynt99]

@poynt99 .Re the graph on the Wicki page you provided a link to . What I find hard to understand is this . The vertical scale on the graph shows drain current . But the higher numbers are at the bottom of the scale and the lower numbers are at the top . From this , I would deduce that the higher the voltage on the gate , the Lower the Drain current .This can not be true in the case of the type of Mosfet we are talking about . What have I missed and what is the significance of the letter "E" in the Drain current numbers . I think what you may be trying to say is that some current can flow between drain and source with zero gate voltage ? The animation however appears to show that about0.5 volts  is  needed on the gate  to permit any drain-source current to flow .

The notation commonly used in science is a "scientific notation", whereby "exponents of powers of 10" are used.

So, a notation of 1E-14 means 1 x 10^-14 and 1E-5 means 1 x 10^-5. The latter expression is a much higher value.

So in summary, the Drain current indeed rises with the vertical axis in that graph.

.99

[Rosemary Ainslie]

This is getting to the essence of it's operation, but one or two key points are still absent in that description.

What may we conclude from that animated graph? Is the MOSFET Drain-to-Source "channel" always connected, or is there a certain V_GS voltage that must be reached first?

http://en.wikipedia.org/wiki/File:Threshold_formation_nowatermark.gif

These are not really relevant Poynt.  In the first instance it's a description of a nanowire MOSFET - and in the second instance they're arguing that the 'bridge' is gapped with electrons.  If you recall the entire premise of my argument is that there are NO ELECTRONS flowing in electric current flow.  What I require are magnetic dipoles.  And a magnetic dipole will bridge the gap across the gate in either direction - which is evidently what is happening.  I'll go into these arguments again Poynty - but it's as clear as daylight to me that you have NEVER even bothered to read up what the thinking is behind all these circuit designs.  How can you comment - if you don't even know the counter argument?  I've taken the trouble to learn classical argument.  Surely you can take the trouble to learn a variation of this?  I'll presume to give you a link to this when I've concluded this post.

Then.  I would be very glad to argue the condition of the circuit with you - and that at length.  But I absolutely refuse to do so on the premise of that schematic that you keep giving us.  It is ENTIRELY misleading.  The CSR is on the negative rail of the supply.  It is nowhere else.  There is absolutely NO requirement for that cap that you persist in putting across the load.  And the Q2 MOSFET does NOT have that zener biased as you've shown it.  Then.  The positioning of the source is TRANSPOSED on Q2 that it ACCEPTS the input from the 'negative signal' from the oscilloscope or the 'positive signal' from the battery - simply because - in terms of their polarities it is still positive according to the MOSFET.  In other words - according to the transposition - the MOSFET now sees the negative as a positive.  As in most things - charge is also relative.  I know you know this.

So.  What I'm really asking is WHY are you going through this circuitous circuit argument?  And WHY do you keep putting that schematic in front of us?  It's quite simply erroneous.  PLEASE amend it as required.  Then we've got a basis for discussion.

Kindest regards,
Rosemary

And just as a reminder - here it is again.  But what it STILL NEEDS is the reversal of the diode at Q2.  Otherwise it is precisely what is required.  And it is PRECISELY what we've got on our circuit except that the zener at Q2 - as mentioned twice already - needs to be changed.


And here's that link.  Please read it.
http://newlightondarkenergy.blogspot.com/2011/04/101-repost-of-8-inconvenient-truth.html

[hoptoad]

snip...

The animation however appears to show that about0.5 volts  is  needed on the gate  to permit any drain-source current to flow .

Correct.

However, power mosfets, in general use with switched power circuits are usually biased at the gate with a nominal 10 volts or more.

With 10 volts or above, applied at the gate to source junction, the mosfet will perform as a "near perfect" switch, with the resistance between the source and the drain approaching zero as a result.

That's why they are so popular in switched power supply systems, e.g, the power supply running inside a desktop computer.

The gate voltage supply is normally current limited via a resistor between the gate and supply or signal.
Mosfets require only a small gate current, as the gate to source controlling junction is voltage not current dependent.

Cheers

[poynt99]

The operation of any enhancement-mode MOSFET is equal on all accounts, except for the recent development of low-threshold varieties, shown in that graph. The important point is that the principle is the same for all MOSFETs.

The I_D vs. V_GS characteristic curve shown is valid and representative of the IRFPG50 MOSFET being used in this circuit. The point of the graph is to show the general relationship between the Drain current I_D, and the applied Gate voltage V_GS. Parameters vary by type of MOSFET, but the characteristics are similar in all.

In summary, the Drain-to-Source channel is "open", OFF (high resistance) when V_GS = 0V. As V_GS increases in a positive direction (N-channel), the channel resistance begins to decrease, until finally the Gate-to-Source threshold voltage is reached (V_TH), and I_D begins to substantially increase. In effect, the MOSFET is beginning to turn ON once the Gate-to-Source voltage V_TH is reached.

.99