Negative Kink Characteristic

125

01:36:20

I was playing around with complex current sources and I got this. At up to around 10V the V-I characteristic is normal (the higher the voltage the higher the current through the load). As the supply voltage passes above 10V the V-I characteristic reverses and the circuit presents a negative resistance in respect to the load. Basically as the voltage of the power supply continues to increase, the current through the load starts falling, and at somewhere around 220V the current falls down to zero. I think it works something like this. The upper current source sets some current limit. Up to that point everything works fine. When the lower current source starts drawing more, the upper one kneels and starts dropping current instead of supplying it, as any current source does, but the lower one tries to maintain as close to the current it has been set to, as it can, so it continues to draw close to the maximum, or at least close to what the upper one gives it. The whole process is controlled by the supply voltage. Very intricate process. 

published 9 years ago

sircube

9 years ago

I noticed that if you increase the current through the load, the behaviour changes and it becomes similar to a standard bjt curve, really strange anyway

nikisalli

9 years ago

Thebugger (can i call you bugzy like how hurz does?) Why don't you try to make a tunnell effect diode with bjts?

thebugger

9 years ago

The current through the load increases to a given point then it starts falling with the increase in voltage. Niki I'm not sure you can emulate the characteristic of a tunnel diode because it's very irregular. First there's a region on positive resistance, then it falls smoothly into a region of negative resistance, but then after a given point it once again rises into a positive resistance. I'm not really sure how, and even if you can emulate that exact characteristic with a bjt. I'm not sure if you're familiar with tetrode vacuum tubes, but they have a similar character, and they've widely been used in the past for oscillators due to that characteristic. Basically you got electrons boiling off the cathode. They pass through the screen grid and further accelerate to the plate, but if the plate voltage is low it will not be able to absorb all of them completely. Most of them will bounce back due to a phenomenon called secondary emission and the current through the plate will fall. So the process looks something like this. First the screen grid doesn't accelerate them enough and they do get absorbed by the plate (this is the region of positive resistance). Then the voltage increases a bit, but the grid accelerates them faster than the plate can absorb, and the current through the plate decreases (this is the region of negative resistance). Usually in this region the screen grid's current tends to increase as the plate current decreases. This reciprocity makes the tetrode suitable for oscillators. And the final step is, that the plate voltage further increases, to a point where it can once again start absorbing all of them easily (again positive resistance). That characteristic is a lot like a tunnel diode.

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