I have a 100 ohm resistor, which was connected to a I-V measurement unit. I then swept voltage from 0 -7 V, but the graph showed a current from 0-0.01 A corresponding to 0-1 V . Why it does not give a current corresponding to 2,3...7 V ? Is there any physics behind it?Please give answer to this basic electronic Ohm's law related question.
The compliance voltage of a constant current source is the maximum voltage across it (or across the load what usually is the same). It depends on the load resistance, the supply voltage and the needed voltage drop across the internal elements of the current source.
For example, look at the attached figure of a transistor constant current source. It is a voltage stabilizer keeping a constant voltage Ve across a constant emitter resistor Re; as a result, the emitter (collector, load) current IL = Ve/Re is constant. The transistor does this "magic" by changing its instant collector-emitter "resistance" (voltage) so that to compensate various disturbances. Thus, if the load increases its resistance, or if Vcc decreases, the transistor decreases its resistance (voltage) to keep the desired current... and v.v. But when the transistor spends all its stocks of resistance (voltage), the "magic" ceases and the current begins decreasing. So the compliance voltage of this circuit is Vc = Vcc - Ve.
Many measurement setups have a compliance current or voltage. In simple words, once the current/voltage source reaches this predetermined value it will do something so it doesn't exceed this value (it can be to stop the measurement, or just keep the values as such as the compliance is not exceeded).
I suggest that you start by looking up the compliance current in your voltage source, I'm guessing it's set to 10mA.
Is the obtained IV curve linear? If so, the compliance current or voltage will not be the reason... Maybe the I-V measurement unit has some input scaling?
As said by @ Lior Kornblum, this has to compliance problem.
If your curve flattens off after 0.01 A, then its compliance is 10 mA. You can set the current compliance to higher values and then do the measurements.
Can you explain what is compliance current or voltage ? any physics related to this
The compliance voltage of a constant current source is the maximum voltage across it (or across the load what usually is the same). It depends on the load resistance, the supply voltage and the needed voltage drop across the internal elements of the current source.
For example, look at the attached figure of a transistor constant current source. It is a voltage stabilizer keeping a constant voltage Ve across a constant emitter resistor Re; as a result, the emitter (collector, load) current IL = Ve/Re is constant. The transistor does this "magic" by changing its instant collector-emitter "resistance" (voltage) so that to compensate various disturbances. Thus, if the load increases its resistance, or if Vcc decreases, the transistor decreases its resistance (voltage) to keep the desired current... and v.v. But when the transistor spends all its stocks of resistance (voltage), the "magic" ceases and the current begins decreasing. So the compliance voltage of this circuit is Vc = Vcc - Ve.
Hello Shamjid,
I shall explain you in simple ways. For a 100 Ohm resistor, you tried to change (sweep) the voltage from 0-7V and expecting the current from 0-70mA. But what you got is just 10mA showing 0-1V sweep.
Some times your measurement circuit might be loading it. Add a simple op-amp buffer if possible and then try again.
Second way is to just increase the current sourcing capacity of your source and then repeat your measurement trials.
Best luck!
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