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| Positive exponentials (against time)in electronics anywhere?Thought "experiment" |
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| Infraviolet:
Just some idle ponderings but... Can anyone think of an example of a positive exponential voltage (between any two points) or current (with respect to time in whichever case) occuring anywhere in electronics? There are plenty of negative expontentials "e^(-const*t)", and of "const - e^(-const*t)", such as in the discharging and charging of capacitors, but what about positive expontentials which run away with themselves, until some practical limit is reached and the behaviour is stopped at a steady state (including by the circuit being ruined in the process). The closest thing I can think of is where the resistance inside a MOSFET rises with the MOSFET's temperature, in which case the temperature can go up expontentially until heat losses reach equilibrium or the mosfet is destroyed, but that's a temperature rising exponentially, rather than a strictly electrical parameter, like a voltage or current. |
| IanB:
It's going to happen anywhere you have positive feedback. Practical examples would be with a comparator, or a Schmitt trigger. If you plot the change in state over a short enough time scale on an oscilloscope you should be able to see the exponential rise of the signal. |
| Benta:
Current through an NTC resistor at constant voltage? Voltage over a PTC resistor at constant current? Both have to be self-heating, of course. |
| twospoons:
Thyristor turn-on? |
| tom66:
Avalanche breakdown (in diodes, zeners > 5.6V) has a positive exponential term in it, if I remember correctly. |
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