Test Circuit Request: Stop Current Before Wire End?

[giantkiller]

My goal is a 20 nanosecond pulse.  The spec-sheet that came with my 555 indicates:

Maximum frequency in astable mode: 2.1 MHz

If my calculations are correct, this is 476 nanoseconds per cycle.  I already know about putting the diode across pins 6 & 7 to get < 50% duty cycle, but I am not sure if I can squeeze a 4.2% duty from the edge of the 555 specification envelope.

I was hoping that I could do this with simple solid state circuitry.  Will I need something exotic and expensive to achieve a 20 nanosecond pulse?

I don't know about stopping the current before the wire ends, but I think I am going to stop this test before it ends.  WTF am I going to do when I get my 20 nanosecond pulse anyway?  It's like giving a hooker to a seven year old. 

You have all the speed you need in the leading edge. That is faster than the CU can react. After that its all easyflow.

--giantkiller.

[gyulasun]

My goal is a 20 nanosecond pulse.  The spec-sheet that came with my 555 indicates:

Maximum frequency in astable mode: 2.1 MHz

If my calculations are correct, this is 476 nanoseconds per cycle.  I already know about putting the diode across pins 6 & 7 to get < 50% duty cycle, but I am not sure if I can squeeze a 4.2% duty from the edge of the 555 specification envelope.

I was hoping that I could do this with simple solid state circuitry.  Will I need something exotic and expensive to achieve a 20 nanosecond pulse?

I don't know about stopping the current before the wire ends, but I think I am going to stop this test before it ends.  WTF am I going to do when I get my 20 nanosecond pulse anyway?  It's like giving a hooker to a seven year old. 

Hi,

See my post #1152 in "user Turbo's replication of SM TPU",
http://www.overunity.com/index.php/topic,1761.msg21223.html#msg21223
on the CMOS version of the 555, the LMC555 or TLC555 (but not the MC1555), that run up to 3MHz in astable mode and the rise and fall time is 15nsec.  Also included in that post a link to an EDN design idea for a pulse generator with independently variable duty cycle and frequency adjustment possibility.
If you want around 20-25nsec rise and fall time you have to use MOSFET driver integrated circuit because the LMC555 is not able to drive as fast as that when the capacitive load at its output is in the nanoFarad range from the gate of any powerFET you may wish to use for switching. Here is a beefy driver (there are faster of course):
http://ww1.microchip.com/downloads/en/DeviceDoc/21419c.pdf

regards
Gyula

[Spherenot]

http://www.josephnewman.com/JN_Theory_by_Hastings.html

As a thought experiment, suppose one made a coil consisting of 186,000 miles of wire. An electrical field would require one second to travel the length of the wire, or in Newman's language, it would take one second for gyroscopic massergies inserted at one end of the wire to reach the other end. Now suppose that the polarity of the applied voltage was switched before the one second has elapsed, and that polarity switching was repeated with a period less than one second.

Now where have I heard this before?

Joseph made a coil with 55 miles of wire.  Who needs nano-pulses when you have a wire this long?

[Spherenot]

Hi,
See my post #1152 in "user Turbo's replication of SM TPU",
http://www.overunity.com/index.php/topic,1761.msg21223.html#msg21223
on the CMOS version of the 555, the LMC555 or TLC555 (but not the MC1555), that run up to 3MHz in astable mode and the rise and fall time is 15nsec.  Also included in that post a link to an EDN design idea for a pulse generator with independently variable duty cycle and frequency adjustment possibility.

Thank you.  The link you posted there looks promising...

But if an output duty cycle different than 50:50 is needed, application of this simple circuit gets complicated. That?s because the usual ways in which the basic RC multivibrator is modified for asymmetrical output timing either allow annoying interaction between output duty cycle and period or degrade the tempco and the PSRR.

I believe that I was running into this problem.

[Spherenot]

You have all the speed you need in the leading edge. That is faster than the CU can react. After that its all easyflow.

I recall reading somewhere here that the trailing edge was all mighty.  That was the big thing that we needed to have happen before the leading edge hit the wire end, no?

Wasn't the trailing edge of the ship supposed to catch-up to the dolphins so the propeller could radiate their meaty energy in a plane axially orientated to the direction of travel, or something? 

You might be right.  I recall Tesla stating first noticing radiant energy when hight current lines were first switched on.  Dolphin safe tuning.