Earl's Corner

[Earl]

Hi All,

here is the test circuit.

Regards, Earl

[Earl]

Hi All,

here is an animated GIF of how my thought experiment would have to function.
The GIF appears not to be animated when viewed in the forum, so it will have to
be downloaded and viewed locally.

Unfortunately, the FET driver ICs don't have 3-state output, so at the moment,
I don't see how to realize this idea in the form of a schematic.

For one coil pair, no problem, but to create a rotating field with FET driver ICs alone
in a differential manner now looks a bit difficult to realize.

Will have to think some more.

Regards, Earl

[Bob Boyce]

@Earl

Interesting concept. The quad coil concept is sound, as 4 phase can work as well as 3. I'm just not so sure about the capacity of flip-flops to handle driving the windings.

I know the point is as much potential switching with as little current as required, but you will find that there will still be some amount of current that flows, even in open ended windings. The goal is to fill and empty the potential as quickly as possible in the wndings. If the device you are using to do that limits inrush / outrush flow of potential by bottlenecking, it will greatly impact performance by slowing down the ramp-up and ramp-down of potential. So even if you are not planning on shoving loads of amps through that wire, you will still want the drive electronics to have the capacity to do the job fast in both directions. Both charging and discharging of the potential.

Bob

[Earl]

Hi All,

bit late with the update since had a lot of trouble.

Decided to try the pulse circuit with 74AC74 flip flops to see what happens.  On a whim, I changed the circuit from last time just a little bit.  Instead of clocking in a "0" on the D input and feeding back Q to Set/ this time I tried clocking in a "1" on the D input and feeding back Q/ to Reset/.

The result was oscillations on the F/F output, which I could not master.

I then went back to the original idea of clocking in a zero and feeding back Q to Set/.  This worked.  At around 5.8 V from a 3-cell lead acid gel battery, the pulse width was around 3.2 nsec with rise and fall  times of around 1.5 nsec.

Very roughly about 3 times faster than the HC74.  There is a slight delay offset of Q to Q/ , they are not really complementary, but we are talking here about very low nsec range.  There are also more overshoot and ringing than the 74HC74.

I grabbed two pieces of plastic-insulated copper wire, each about a meter long and soldered one each to Q and Q/.
The result was different than I expected.  The output swing did not decrease, but there was now a double pulse on the outputs.  The second pulse actually has more amplitude than the first, actually swinging above the Vdd supply voltage.

The reason for this is most likely the fact that one output is fed to a Set input.  If there is a reflection from the ends of the wires returning to the F/F, then this reflection could trigger the Set input.  It will be interesting to see what happens with longer wires.

When bending the wires into a loop and shorting the ends together, the F/F outputs disappeared; too much load from too short a wire.

This double-pulse effect will probably disappear when using a buffer amplifier such as a FET driver.

So, I have lots of experiments to try.  Will post some scope screen shots soon.

My suspicion is that I will end up using 74HC logic, together with a FET driver.  At first I will try with just the FET driver, but no FET.

Regards, Earl

[Earl]

Hi,

Please see the attached PDF update showing test results of a 74AC74 pulse circuit.

Regards, Earl