Fighting with computers

Computers are not always friendly.

Thursday, November 13, 2014

Another one bitten by the bug

While I have been doing electronics since I was a kid I never owned an oscilloscope before. At a local meeting of Arduino users a colleague mentioned me there was a very good offer of a four channel sampling oscilloscope. Not that I need to use it very often but I was curious enough to see how instruments have evolved lately I decided it was about time to have my own scope so it was kind of a birthday gift I bought to myself (if that makes any sense).

First thing I have measured, just because it's right next to me is the the ringing of my 3D printer's hotend PID regulator output. It has been mentioned voltages can get pretty high over there in RAMPS boards and boy, that is true. At around a 50-volt spike is produced when the load is switched off. And the real value can only be appreciated if you freeze the sampled signal and expand widely the time axis, as the spike duration is below 1us. I guess total energy is so small the MOSFET is not really damaged (as it has been sitting there for three years now without stop working). Values in the order of micro Joules seems to be safe as the STB55NF06L is avalanche tested and the single pulse avalanche energy is 300mJ.

This second image shows the moment the heated bed of my printer is switched off. It shows how the highest peak is actually triggering the avalanche mode in the MOSFET (avalanche voltage is rated 60V).

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