[time-nuts] fast edge, rise time.
Bob Camp
lists at rtty.us
Thu Dec 26 12:03:11 EST 2013
Hi
If you go the Krytron route you probably will need some fairly fancy transformers as well….
Bob
On Dec 26, 2013, at 11:19 AM, Jim Lux <jimlux at earthlink.net> wrote:
> On 12/26/13 8:07 AM, ct1dmk wrote:
>> Hello,
>>
>> I'm willing to generate a pulse (of some few hundred volts)
>> by discharging a capacitor into a pulse transformer
>> I'm solely interested is the active edge (call it either rise or fall
>> depending on the
>> wiring of the output of the transformer).
>>
>
> ns risetime pulses sounds like fairly straight forward radar stuff.
>
> the inductance of the transformer is going to be your challenge, depending on the energy level. What about a non-transformer alternative? Can you just charge your cap up to the few hundred volts and have a switch that can take the voltage?
>
> How much energy do you need? You said a few hundred volts, but is that microjoules, joules, or kilojoules?
>
> A small triggered spark gap would be one way. There's also the ever popular krytron, which has very good timing accuracy.
>
> YOu might look for circuits used for exploding bridge wires (EBW)
>
>
>> The target is 4ns, while ideas seemed to be clear at some point, now I'm
>> having doubts if better to use a MOSFET or a bipolar transistor
>> as the switch element. Experiments with MOSFETs presented me some
>> difficulties charging the gate capacitance having some trouble to
>> achieve something in the 4ns region. Well 4ns seems hard whatever device
>> anyway.
>
> You want some sort of RF transistor here. What about one of the new LDMOS FETs: some have fairly impressive voltage handling, and if they work at 1 GHz for radar applications, they will work for you.
>
> What about stacking a bunch of MMIC RF amplifiers (e.g. like the ERA or GAL from minicircuits)
>
>
> Other traditional approaches to fast pulse generation are avalanche transistors.
>
>
> There's also a variety of interesting pulse forming networks that can generate fast rise time high voltage pulses. Blumlein arrangements are one. Your 100ns pulse is fairly long for a transmission line scheme, though (20-30 m of coax)
>
>
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