Avalanche pulse generator- part 2

I build a more permanent version of the pulse generator with some changes. The comparator wasn’t working very well with the 1V reference I was using. I made some measurements with different voltage references and got this:

Vref Vfeedback Vout(measured) (R2/R1+1) Vout(calculated) Error[%]
0,282 1,1 76,8 69,03 19,47 -294,5
0,759 1,087 76,6 69,03 52,39 -46,2
0,953 1,092 77 69,03 65,78 -17,0
1,218 1,258 88,7 69,03 84,08 -5,5
1,243 1,283 90,3 69,03 85,80 -5,2
1,499 1,505 106,3 69,03 103,47 -2,7

The feedback loop was working and the converter regulating but the output value didn’t correspond to the one set it with the feedbacks resistors. The difference between the reference voltage (Vref) and feedback voltage (Vfeedback) is lower with a reference above 1,2V (another source of error is the lack of precision resistors in the feedback divider). and increasing the reference value gives a lower error (difference between the measured and the calculated Vout).  At the end I just put a potentiometer to regulate the reference and tweaked until the converter output was near 90[V].

I started with the oscillator

Multivibrator

Then added the step-up

step up added

And test it

testing the step up

Added the voltage doubler

voltage doubler added

… and test it again…

voltage doubler test

I made a mistake while connecting the oscillator to the step-up. I soldered a cable to the wrong output and was using the inverted signal with a short ON time and a longer OFF time. After changing the output the voltage increased a bit, but  not that much (something like 115[V]). Then soldered in the reference and the comparator.

comparator

Then I connected all together, put the resistor divider to get the voltage feedback and set it to 80V

dc-dc converter set it to 80[V]

Finally soldered the transistor, 50 ohm termination and BNC

Avalanche pulse generator

The board with the different blocks labeled,

Avalanche pulse generator

and finally made some measurements.

Avalanche pulse generator

The formula to calculate the bandwidth based on the rise time is BW=0.35 / rise time [ns], I measured somewhere near 2.5 [ns], but that is a bandwidth of 140 MHz. That’s a lot higher from what I was expecting (I have a DS1052E without the bandwidth hack, so it’s 50Mhz). I’m probably doing something wrong but I don’t know what…

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5 Responses to Avalanche pulse generator- part 2

  1. Pingback: Avalanche pulse generator- part 2 - Arduino collector blog

  2. Rik says:

    Hello
    It’s quite possible for a scope to have a higher bandwith then advertised. The advertised bandwith is what a scope should always reach, no matter what.
    So it is quite common for scopes to be a tad faster.
    As your 50Mhz scope is capable of 100Mhz with a software hack it’s possible it can actually measure 140Mhz altough the pricision might be a bit flawed. (a 1V signal may measure as a 0.8V signal for example)

    Rik

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