Avalanche transistor Fast Rise Time Problem

Thread Starter

iraquois1

Joined Feb 27, 2020
16
Hi. I am trying to get 250V pulse with rise time of maximum 2ns on 50ohm load. Right now I am just trying to see avalanche pulse like in the picture my supply is 220V DC. I am using ZTX415 and its simple configurations like in ZETEX application note HERE.
ztx415.png

Instead of using coaxial cable I used 70pF capacitors. (I also tried using 1m -2m coaxial cable with open end)
But the signal I can see on 50ohm is like this:

LeCroy24.jpg

I tried changing ZTX415 and anything but this didn't came into my mind since it is very basic circuit.
What might be the problem here? What are your advices?

* I am driving the transistor with arduino and giving 10us pulses every second.
 

ericgibbs

Joined Jan 29, 2010
11,156
hi i1,
I used the ZTX415 in my pulsed lasers driving a LD163 triple junction laser, the best rise time I could get was 5nSec, which was OK for my units.
Like Fig 11a in the datsheet.

I will be surprised if you can get a rise time of 2nSec.

Can you post a layout of your project, also more information on the way you are measuring the pulse.

E
 

Thread Starter

iraquois1

Joined Feb 27, 2020
16
Actually there is no layout : )). I did it on stripboard (to find out if I can achieve some results).

avalanche circuit.png

I measure it from lecroy 1Ghz oscilloscope.
 

ericgibbs

Joined Jan 29, 2010
11,156
hi Carl,
I am trying to get the TS to post a shot of the circuit and layout, as you know at these switching speeds and currents, the layout and termination is critical.
Eric
 
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