moinmoin

hi
i need help with a battery charger for a NiMH battery pack consisting of three AAA batteries so 3.6v.
the charger has to be as small as possible and it sits a meter away from the batteries to be charged.
the batteries will be attached to the charger most of the time so there needs to be some kind of safety regulator which prevents them from overcharging.

thank you for suggestions
m

Ubergeek63

You could try one of TIs BQ2000 familly

moinmoin

hey
thanks for that ...
what are you suggesting exactly ?
i'm not very familiar with electronics (just starting)
i looked it up on google but don't get what it actually is ...a regulator or charger with regulator ...or....?
could you please explain more in detail what i have to do..
thanks for further advise
m

Ubergeek63

the BQ2000 itself is a fast charge switching chip.
http://focus.ti.com/lit/ds/symlink/bq2000.pdf

The BQ2002 is meant for a current limited supply that it just turns on and off:
http://focus.ti.com/lit/ds/symlink/bq2002f.pdf

The BQ2057 is a linear:
http://focus.ti.com/lit/ds/symlink/bq2057c.pdf

moinmoin

hi Ubergeek63
thanks for this links.
i think the bq 2000 is exactly what i'm looking for.
is it possible to just use the Peak Voltage Option (without temp. control etc)?

"Peak Voltage (NiCd, NiMH)
The bq2000 uses a peak-voltage detection (PVD) scheme
to terminate fast charge for NiCd and NiMH batteries.
The bq2000 continuously samples the voltage on the
BAT pin, representing the battery voltage, and triggers
the peak detection feature if this value falls below the
maximum sampled value by as much as 3.8mV (PVD).
As shown in Figure 6, a resistor voltage-divider between
the battery pack’s positive terminal and VSS scales the
battery voltage measured at pin BAT." page 5 from the bq 2000 link you've send

there is one more thing which i forgot to mention: the +/- cable coming from the charger should maintain the power (3.6v) while charging so the object (in this case an led light) can still be operated while being charged.

is the peak voltager charging regulator still able to detect the battery status in this case?

thanks for advise, it is much appreciated as i am still a beginner in electronics.
m

audioguru

A "3.6V" Ni-MH battery reaches 4.5V or more when it is quickly and is fully charged.
A few other battery charger circuits can power a device while it charges its battery.

__________________
Uncle $crooge

Ubergeek63

As the circuit works as a current source, it really does not care if you are running the load at the same time. I, as a matter of fact, do that myself.

The trick is that if you are fast charging the battery the charge rate will be reduced by the load current. This works fine if your load current is less than half the charge current. Since it is based on peak voltage it will still terminate the charge cycle reliably.

moinmoin

great!
what kind of resistors do i need to create this voltage divider?
do you know a more specific circuit which explains in detail what i have to do with the bq 2000 ic to work? i need a description for stupid:-)
thanks for all the advise so far !!!
m

jai_prakashmurugan

how to control the current in bq2002f with circuit diagram

ghx420

please see the attached file.It's a MCU controlled charging circuit.The determination:negative delt V, Zero delt v,deltT/delt t,MAX deltT,Tmax,Vmax,MaXtime.

jason@gamil.com

Attached Files

84K4-NIE.pdf (69.9 KB, 4 views)