# Help me! Charging time of capacitor circuit?

#### govinda

Sep 1, 2013
1
I need to develop a circuit to measure charging time of capacitor
I am kind of less in practical knowledge (this is my first project)
So far I have thought of giving a reference input and capacitor voltage to comparator
then there is counter that will count the number of time it will go high
then the time divided by the no. of times it will go high will give me the charging time that will be displayed on LCD
Is this method Okay? Will it work?

Can any one please draw me a detailed circuit daigram

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,901
For what purpose do you need to measure the charging time? Is this homework or an assignment?

What capacity does the capacitor have?
What is the charging current?
What is the charging voltage (end of charge, capacitor charged)?
Addendum: A capacitor is never fully charged. You can always put some more charge into it by raising the voltage (until you reach the limit defined by the max. voltage of the capacitor before it starts to break down). This is very different from a battery which has a limited capacity beyond which no more charging is possible.

The setup is basically very simple:
- Make sure the capacitor is discharged
- Apply charge current to the capacitor and start a counter at the same time
- Measure the capacitor's voltage (e.g. using a comparator).
- When the capacitor's voltage has reached the end-of-charge voltage, stop the counter
- read the counter and convert the number to the equivalent time (t=count/frequency).

Last edited:

#### rinchan6

Aug 27, 2013
42
you can use LTSpice

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,901
I beg to disagree.
Any simulator like LTSpice is not a tool to develop a circuit. Simulators are there to verify the behavior of a circuit that needs to be designed/developed before. A simulator will not tell you whether any combination of circuit elements is "correct". It will show you, what this circuit does. It is up to the developer to know and decide how to connect components to achieve a certain behavior and it is also up to the designer to decide whther the observed behavior does make sens (is correct).

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507

"In theory, there is no difference between theory and practice. In practice there is."

In theory, the time to change a capacitor can range anywhere from zero to an infinite time. What often matters the most is your definitions of "charged", and "zero".

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