# Current variations.

Discussion in 'General Electronics Discussion' started by Ravi kant, Oct 16, 2016.

1. ### Ravi kant

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Oct 11, 2016
Hello Seniors.
I'm quite confuse with current!
Since we know that current varies with respect to the load over a fixed voltage supply.
So how can a charger circuit give a constant voltage and current as well or its just my misunderstanding?
I want to understand the logic behind it.
Thank you ☺

2. ### Alec_t

2,844
760
Jul 7, 2015
It can only do both simultaneously for one specific constant load resistance. A battery on charge is not a constant load, so a charger will usually provide a constant voltage or a constant current, depending on the required battery charging profile.

3. ### BobK

7,682
1,686
Jan 5, 2010
Yes, you misunderstand. If you are talking about a cell phone charger, say rated at 5V 1A, the voltage is held constant, the current is the maximum current it can put out, and it varies with the load.

Bob

4. ### AnalogKid

2,371
661
Jun 10, 2015
Your understanding. There are several basic kinds of battery charger circuits, based on the battery type/chemistry being charged. The smart ones have several modes and adjust themselves automatically based on monitoring the battery terminal voltage. These can start out in a constant current mode, then shift to constant voltage mode as appropriate.

Unitrode (now TI), Linear Technology, and Maxim make charger controller chips. Read a few datasheets; they have pretty good explanations.

ak

Arouse1973 likes this.

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Oct 11, 2016