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Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
I see a couple of can crushers out there, but I'm not looking for that much power (<10 joule, for a xenon flasher) and I want to do it on the cheap.
Cheap IGBTs (and Thyristors) all seem to top out at around 600 Volt, so solid state Marx is not an option. Large ratio pulse transformers are slow. The only configuration which seems doable on the cheap is an adder. I was thinking something like this. Which would be around 5$ of components a stage if I wind my own pulse transformer ... I could see how trying to pull up the power planes of an entire driver circuit by kVs in 100 ns might have unintended consequences though.
Anyone know of any existing schematics for something like this or alternatives?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Pinky's Brain wrote ...
I see a couple of can crushers out there, but I'm not looking for that much power (<10 joule, for a xenon flasher) and I want to do it on the cheap.
Cheap IGBTs (and Thyristors) all seem to top out at around 600 Volt, so solid state Marx is not an option. Large ratio pulse transformers are slow. The only configuration which seems doable on the cheap is an adder. I was thinking something like this. Which would be around 5$ of components a stage if I wind my own pulse transformer ... I could see how trying to pull up the power planes of an entire driver circuit by kVs in 100 ns might have unintended consequences though.
Anyone know of any existing schematics for something like this or alternatives?
You can make an excellent fast pulse generator with series arrangements of high voltage avalanche transistors (when one goes the rest in the string are all over-voltage and go too) I have a circuit diagram somewhere, together with details of commonplace cheap HV transistors that can be made to avalanche in a repeatable way, so if you're not in a very great hurry, I'll find them for you in the next day or so.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Pinky's Brain wrote ...
Googling for high voltage avalanche transistors did the trick ... 2N5551's are 6 cent a pop.
Can these things source 2 orders of magnitude more than their rated continuous current in pulse use though to give a nice flash with a xenon tube?
Why not use the avalanche transistor to switch on the gate of a power MOSFET, as described, using a very simple circuit, here: Nanosecond Switching Using Power MOSFETs Baker et al
A 3 nanosec rise time is better than being slapped round the face with a dead halibut, eh?
But if you want to keep MOSFETS out of it - understandable for artistic or aesthetic reasons - then you can connect your series avalanche strings in parallel. Figure 15 in this Zetex application note has a funky parallel avalanche circuit claimed to produce 100A pulses:
I couldn't afford to buy buckets of the ZTX415s, so I bought a few hundred of the 2N5551s, but haven't got round to using them yet. But when I feel the need for a big thyratron trigger pulse coming on, I have them there all ready to go.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Welcome.
Can you give us more detail about your pulser requirements (voltage, risetime, pulsewidth, jitter, load)?
Sounds like you want to flash a xenon lamp by applying a HV pulse to its main terminals, without using a trigger electrode. Why does the usual configuration (in 99% of all xenon flashlamp drivers, whether made in 1960 or 2010) not work for you? (Medium voltage DC-charged capacitor wired to flashlamp; HV trigger on third electrode, from millijoule capacitor discharge into a pulse transformer.)
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
I want to build my way up towards getting all the components for a dye laser ... and I thought I'd start with something which could draw some nice sparks. Triggered low voltage xenon discharges are slow and open air spark gaps noisy in more ways than one, so I'd like something solid state. The DIY solid state schematics I could find were all for either ridiculous power (can crushers) or fairly continuous operation (Tesla).
If there's really no other way though then a simple DC HV supply going into a blumlein with an air gap will do I guess (same as the TEA lasers).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Pinky's Brain wrote ...
I want to build my way up towards getting all the components for a dye laser ... and I thought I'd start with something which could draw some nice sparks. Triggered low voltage xenon discharges are slow and open air spark gaps noisy in more ways than one, so I'd like something solid state. The DIY solid state schematics I could find were all for either ridiculous power (can crushers) or fairly continuous operation (Tesla).
If there's really no other way though then a simple DC HV supply going into a blumlein with an air gap will do I guess (same as the TEA lasers).
Professor Mark Csele's Homebuilt Lasers Page Flashlamp Pumped Dye Lasers
Mark refers to a dye laser he's seen elswhere:
"Food for thought: The critical component in building a flashlamp-pumped dye laser is the capacitor. Regular electrolytic caps discharge far too slowly for such a laser which requires discharge times in the microseconds to work. What about using a capacitor (homebuilt) of high voltage and low capacitance? Since E=0.5*C*V2, employing a high voltage allows the use of a small capacitance and hence (potentially) faster discharge times. It would be easy to build and would guarantee a fast enough discharge to get the laser to work.
An article I came across took this approach. The authors used a 7nF, 50 kV capacitor (Only 9 Joules of energy). The "lamp" wasn't a lamp at all but rather a confined spark in open air (enticing for an amateur again since no vacuum pump is required). The result is a super-fast pump (70 nS discharge) resulting in a very low threshold energy.
It may be possible to use lower voltages (say 20 kV) with an air flashlamp at a lower-than-atmosphere pressure (say 500 to 760 torr) to make the device triggerable (using a high voltage trigger like any other flashlamp). Since the voltage decreases, the capacitance (and hence discharge time) will increase and a larger cap is required (Threshold energy will increase). My original thought was to build a capacitor from alternating plates of aluminum foil and mylar all immersed in a bath of insulating oil to make a compact capacitor unit."
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Jon Singer puts more than 9 joule through a cheap Xenon tube with a spark gap, so using an open air arc light isn't really necessary at these energies. Considering the difference in efficiency you'd need huge power to make an atmospheric pressure air arc lamp a good option.
A DIY blumlein with oil/mylar/copper foil capacitors could undoubtedly do huge voltages and fast flashes with spark gaps. I found this paper where they did it with a water filled spark gap with a rise time of 5 ns. Also another paper where a 10 joule discharge through a water spark gap crashed all computers in a 50 feet radius :)
Can electrolytics really not do fast rise times BTW? The affordable ones are obviously no good for complete pulse discharge, but looking around people seem to be getting pretty good rise times out of electrolytic fed IGBTs with small amounts of discharge.
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Looking for a low power fast solid state pulser design
