In the theoretical circuit configuration shown in the attachment, I have been looking at the directions of the capacitor charge and discharge currents.
The circuit undergoes an instant change of input voltage from 0 volts to +1volt, achieved for illustration purposes by a perfect changeover switch. The voltage sources are assumed to be perfect with zero internal impedance.
When the input goes to +1volt the capacitor discharge current appears to flow in the reverse direction through the positive power supply which seems counter intuitive and I will be grateful for a more experienced opinion to confirm if my understanding is correct.
I understand about the CR time constant and exponential aspects of the charge/discharge of the capacitor, but at the instant the input transits from 0 to 1volt, its the direction of the capacitor discharge current into the positive terminal of the power supply that somehow seems counter intuitive. So I'm not sure my understanding is correct.
Diagram A
Assume the input has been at 0 volts for long enough for the capacitor to be charged to the supply voltage of 10 volts. The current to charge the capacitor has flown out from the positive terminal of the supply. In this fully charged state there is now 10 volts at each end of the resistor so there is no current flowing through it, and hence no further current flowing out from the supply.
Diagram B
Now the switch is thrown and the input goes to +1volt. At that instant, this input voltage is in series with the 10 volts across the capacitor and the voltage at point P thus goes up to +11volts. There is now 1 volt across the resistor so a current equal to 1/20 amps must be flowing in the direction towards, i.e. through the supply.
Diagram C
This current will decrease exponentially to zero as the capacitor discharges to 9 volts i.e. to the state where point P is again at +10volts.
So, is this analysis correct?. Does the discharge current flow into the positive terminal of the power supply?
Thanks for any comment you can offer.
Mod: Added clip from PDF
The circuit undergoes an instant change of input voltage from 0 volts to +1volt, achieved for illustration purposes by a perfect changeover switch. The voltage sources are assumed to be perfect with zero internal impedance.
When the input goes to +1volt the capacitor discharge current appears to flow in the reverse direction through the positive power supply which seems counter intuitive and I will be grateful for a more experienced opinion to confirm if my understanding is correct.
I understand about the CR time constant and exponential aspects of the charge/discharge of the capacitor, but at the instant the input transits from 0 to 1volt, its the direction of the capacitor discharge current into the positive terminal of the power supply that somehow seems counter intuitive. So I'm not sure my understanding is correct.
Diagram A
Assume the input has been at 0 volts for long enough for the capacitor to be charged to the supply voltage of 10 volts. The current to charge the capacitor has flown out from the positive terminal of the supply. In this fully charged state there is now 10 volts at each end of the resistor so there is no current flowing through it, and hence no further current flowing out from the supply.
Diagram B
Now the switch is thrown and the input goes to +1volt. At that instant, this input voltage is in series with the 10 volts across the capacitor and the voltage at point P thus goes up to +11volts. There is now 1 volt across the resistor so a current equal to 1/20 amps must be flowing in the direction towards, i.e. through the supply.
Diagram C
This current will decrease exponentially to zero as the capacitor discharges to 9 volts i.e. to the state where point P is again at +10volts.
So, is this analysis correct?. Does the discharge current flow into the positive terminal of the power supply?
Thanks for any comment you can offer.
Mod: Added clip from PDF
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