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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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When you say pulse, it really depends on how much of a "pulse" you want to see. If you want to see sharp edges, and measure risetimes accurately, you are going to need a lot more bandwidth than 100MHz to accurately see a 100ns pulse. (I assume a 100ns pulse has some very fast rise and fall times)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
EasternVoltageResearch wrote ...
When you say pulse, it really depends on how much of a "pulse" you want to see. If you want to see sharp edges, and measure risetimes accurately, you are going to need a lot more bandwidth than 100MHz to accurately see a 100ns pulse. (I assume a 100ns pulse has some very fast rise and fall times)
Well, the 'pulse' will be a rising current pulse on the primary. I suppose I'll have to add a resistance, and 'scope the voltage accross it to measure the current (I'm not certain yet).
The idea I have is to charge a capacitor to 300V from an SMPS, then see how fast the current rises in ~100nS. I've not done the maths yet as far as stored charge/amps per second goes yet, but I have plenty of BIG 450V capacitors, as well as loads of smaller ones.
I've been reading up on 'volt-seconds', etc., but most of what's on the internet relates to step-down flyback converters, rather than step-up, but the gist of it seems to be that the higher the voltage, and the lower the inductance of the primary, the faster the current rise, and magnetization/saturation of the core. I'm going to have to play with air gaps as well, but first I want some idea of rise times in the primary.
Nothing is fixed yet, but I will need to keepn the pulse in the primary to a few hundred nanoseconds at most, and the shorter the better, from what I've read.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Steve Ward wrote ...
you might be disappointed to find that the self-resonance of the HV winding is hundreds of kHz or something substantially lower than 1MHz. This means you wont get nearly the output voltage you are hoping for. You might as well be driving a tesla coil, a proper transformer will have too much self capacitance for 1MHz and enough kV to spark through air.
Well, I've worked out that a primary with a resonant frequency of ~1.5MHz will allow the current to rise to 'near maximum' in ~100nS.
It follows that a secondary with a resonant frequency of ~150kHz will allow the voltage to rise to near maximum in ~1uS, I think.
I'm just trying to get some idea of the magnitude of the figures involved. I could reduce these frequencies considerably and still get multiple sparks.
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I need something faster than a 555 timer.
