Battery Charger - DS2714 - Current Source?

Hello,

I am wanting to make a super safe, nimh/nicd smart battery charger. After looking around, I've decided to use the DS2714 chip for my design. If you have any other chip suggestions, please let me know.

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I think I pretty much have the schematic of how to get the DS2714 working, except for the current source. I found no information on the current source in the data sheet, except "current source". Does anyone know what current rating my current source should be? Also, I will be using a regulated 5V to power this charger, how can I turn that into a current source?

Thanks!

hi Fred,
Have you checked Maxims application notes?

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Whats the voltage/AHr capacity you want to charge?

You can configure a 7805 or LM317 as a current source.

The current source in the datasheet is 2A. it charges each of 4 cells for 1/2 a second each 2 seconds, minus a small amout of time where each cell is tested.

hi,
as 'agu' points out a 2Amp current source is required for the 4 cell charger in the application data.

A 7805/L317 isnt upto the job, you require a similair regulator but with a minimum continous current of say 3amps.

Extract from data sheet.

Thanks for the information guys! I didn't see that 2A in the datasheet anywhere, I must have been blind.

Unfortunately, my source power has a maximum current of 500mA. Would that work with this chip (just take 4x as long) or do I need a totally new chip? Any recommendations?

Thanks again!

The IC is a fast charger for individual Ni-MH cells. It times out after a max of 10 hours. 2500mAh AA cells need 20 hours or more at 500mA/4.

How many cells do you need to charge?

If it's just one then you could use a switching regulator for your current source and get 1A@2V from 500mA from 5V@500mA which would cut your charging time in half.

You really need a much higher current power supply, I'd recommend a PC power supply which can supply a lot of current and is quite cheap to.