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  #1  
Old 08-08-2008, 03:01 AM
kender kender is offline
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Question High voltage nanosecond pulse generator

Colleagues,

Could anyone suggest a schematics or a reference for a high voltage pulse generator? I need a 500V pulse 10ns long or sorter. Negative spike from 500V to 0 and back to 500V would work. I have a schematic for an old (1977) pulser, but the SCR that's used there has been discontinued. I know how to generate a nanosecond pulse at the logic levels. But what would be a good topology for the high voltage "switch"? MOSFETs have gate capacitance that needs to be charged within a few nanoseconds. SCRs (which I, unfortunately, don't have experience with) have their own problems too.

Enlightenment will be appreciated!

- Nick
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Old 08-08-2008, 03:45 AM
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Sounds like you may be looking for IGBT's.
http://en.wikipedia.org/wiki/IGBT
http://www.powerdesigners.com/InfoWe...BTs/igbts.shtm
http://www.st.com/stonline/products/...gbts/igbts.htm

They aren't a complete circuit - this is just an introduction to a relatively new type of device.
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Old 08-08-2008, 04:08 AM
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What sort of load do you need to drive with this pulse?
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Old 08-08-2008, 04:39 AM
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How about a spark gap?
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Old 08-08-2008, 07:41 AM
kender kender is offline
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Quote:
Originally Posted by SgtWookie
Sounds like you may be looking for IGBT's.
Thanks for this tip! I'll look into IGBTs.

Quote:
Originally Posted by Ron H View Post
What sort of load do you need to drive with this pulse?
The load is going to be an ultrasonic transducer. 50 to 300 Ohms with some capacitance to it. I don't have a datasheet for the transducer at the moment, but I will know what the load is soon.

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How about a spark gap?
I don't know how. I wish I knew.
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Old 08-08-2008, 06:23 PM
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You need to consider the transient (capacitive) current requirements as well the resistive load. Remember I=C*dv/dt. If you need 5ns rise and fall times into 100pF, for example, that's a peak current requirement of 10 amps. Not trivial. If all the capacitance is in series with the resistance, then you just need to consider the resistive component.
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Old 08-09-2008, 06:32 PM
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Default Load impedance

Quote:
Originally Posted by kender
Quote:
Originally Posted by Ron H
What sort of load do you need to drive with this pulse?
The load is going to be an ultrasonic transducer. 50 to 300 Ohms with some capacitance to it. I don't have a datasheet for the transducer at the moment, but I will know what the load is soon.
I've clarified what the load is going to be. 50 Ohms.
Quote:
Originally Posted by Ron H View Post
You need to consider the transient (capacitive) current requirements as well the resistive load. Remember I=C*dv/dt. If you need 5ns rise and fall times into 100pF, for example, that's a peak current requirement of 10 amps. Not trivial.
My plan is to charge a large capacitance from a relatively small power high voltage supply. Then this capacitance will fulfill the peak current requirements.
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Last edited by kender; 08-10-2008 at 08:31 AM. Reason: touch up, improve clarity
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Old 08-09-2008, 07:16 PM
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Thingmaker3's spark gap suggestion might be the easiest (and cheapest) solution.
It's generally accepted that 3,000,000 volts are required to jump an air gap of 1 meter near sea level.
This translates to 76.2v per mil (0.001"). So, a spark gap of .0065" (rounded) should cause the 500v supply to ionize and jump the gap at right around 495v. The duration of the spark would then depend on your load impedance and the size of your capacitor.
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Old 08-10-2008, 08:01 AM
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You can also buy a GDT (gas discharge tube) or look at a MCT device.
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Old 04-26-2009, 05:26 PM
Ruptor Ruptor is offline
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Hi
I know this thread is old but I just saw this circuit and thought it might help others to build a more modern version of a nano pulser.

http://www.case.edu/cse/eche/ESA2008_Proceedings/H3.pdf

Incidently using gas breakdown in a spark gap requires that the gas breakdown voltage be exceeded it doesn't matter what the gap is to start with the voltage has to exceed Vbrk. Reducing a gap does not make it break down at a lower potential.

Last edited by Ruptor; 04-26-2009 at 05:29 PM. Reason: extra info
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