Hello, today I had a little fun trying
to build my first transistor avalanche pulser.
To my great surprice after half an hour
I had the first pulses out of the circuit.
The schematic is the classic AN47page 93.
The components used were what I had at hand
at the moment:
1u On voltage input followed by a
1Mohm to transistor collector and
a trimmer capacitor of something around 2-10pf
(not sure about this, my capmeter doesnt fare
well at these resolutions) to ground; on the emitter
i used a 56ohm; 75kohm on the transistor
base, simply because I was misled by color codes
and was thinking it was a 15kohm :)
The first transistor didnt avalanche at all, i dont
remember the code, the second was a bc238 that
avalanched at about 240V but with slow pulses.
The third transistor started generating cute
pulses at 140-150V, it's an stc945.
the pulses are very steep but it seem that
are a little high voltage, the rep. rate
is around 28kHz.
I started using the sds7102 to check for
initial setup, I used its' probes that are
low cost 100MHz probes that come with the
instrument, are marked P5100.
I used the same probes for 3 scopes compensating
them for each instrument.
Here is one of the pics of the pulser:
This is the pulse as seen from the
philips PM3217, this is a 50MHz scope with a 7nS
declared risetime, the first is the pulse adjusted
to show the risetime, approx 4nS
here the pulse as seen at 10nS per div and 1V (x10)
per div
here the pulse seen from the sds7102, a DSO 1GSps 100MHz
(others reported that the input BW is much is wider than this)
risetime about less than 2nS, rep. rate 28kHz:
And here we come in topic :)
This is the good channel of the 7A26 in the R7103
adjusted for risetime: 1,4nS, TB is a 7B92A:
amplitude something around 30-40V on the probe tip
What do you think?
Any improvement suggestion about the circuit is welcome!
I dont know if there is a meaning in these, I see very
steep pulses but I'm using cheap probes.
What could I do to not use these ceap probes, apart
buying a 7A29 and a pair of good Tek probes (will not
happen soon :) ?
Can I conclude that the Philips has a 4nS risetime?
Now I'll build a power supply to have the thing powered
from some battery.
Fabio.
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