How Can I Accurately Measure Voltage Drop across a Capacitor?

[simoncastle]

Hi all,

Here's the problem!

I am attempting to create a leakage current test suite. Basically it centers around cutting the voltage reference supply to a capacitor and measuring the voltage drop. Similar to the one in the attachment.

I figured that to determine the drop it would be a simple case of V at start minus V after time delay.

However a colleage told me that because of the exponential decay of capacitors this simple equation wouldn't be enough to accuratly determine the voltage drop.

Any ideas?

Thanks!

- Si

 

[Redbelly98]

I'm assuming you want to measure the parallel resistance (which causes the charge to leak) of the capacitor.

You can use an exponentially decaying function for the voltage:

$$V_t = V_{ref} \ e^{-t/(RC)}$$
where Vt is the voltage after t seconds. Solve the equation for R after measuring all other quantities (Vt, Vref, t, and C)

 

[oswaler]

I would suggest using a mathematical model to accurately determine the voltage drop across the capacitor. The equation you mentioned, V at start minus V after time delay, is a simplified version that does not take into account factors such as the capacitance value and the resistance of the circuit. These factors can significantly affect the voltage drop and cannot be ignored.

One possible way to approach this problem is to use the formula for the time constant of a capacitor (T = RC) and the equation for the voltage across a charging capacitor (V = V0 * (1 - e^(-t/RC))), where V0 is the initial voltage and t is the time delay. By plugging in the appropriate values for R and C, you can accurately calculate the voltage drop across the capacitor at a specific time.

Additionally, it is important to consider the accuracy and precision of your measurement equipment. Small errors in the measurement of voltage can lead to significant discrepancies in the calculated voltage drop. Therefore, it is important to use high-quality equipment and carefully calibrate it before conducting the test.

In conclusion, accurately determining the voltage drop across a capacitor requires a more complex approach than a simple calculation. By using mathematical models and high-quality equipment, you can obtain reliable and precise results for your leakage current test suite.