Technical Support and Design Advice...

Hi Shawn,

I am curious, has anyone done a full energy transfer calculation on the efficiency of wireless power verses the standard battery recharge circuit?

If you want this approach to work, you need to establish if it is cost effective.  I worry about the power losses verses the speed to charge.

Has it been tried with super capacitors?  That might be a better approach for fast and efficient charging.

Just a thought,

DAB

Hello Shawn,

I've seen that more people are trying to charge multi-cell batteries, and must thus use a converter at the output. I thought it might be nice to share my ideas here, as starting point for others, and to receive some feedback myself.

My idea is to use NiMH AAA batteries, and I need a very small circuit. I guess the easiest configuration is to use a bq2002 to control the charger, and use a LMR62014XMFE/NOPBLMR62014XMFE/NOPB or a LMR62421 as step-up converter to generate the necessary charging voltage.

If you have any serious doubts about this setup I'd like to know!

Hi DAB,  probably best to view the Qi WPC comments on efficiency of wireless power...  http://www.wirelesspowerconsortium.com/technology/transfer-efficiency.html

If you find anything on the use of "super capacitor" and wireless power please feel free to share...

" The figure shows that...

• The efficiency drops dramatically at larger distance (z/D > 1) or at a large size difference of the coil (D2/D < 0.3)
• A high efficiency (>90%) can be achieved at close distance (z/D < 0.1) and for coils of similar size (D2/D = 0.5..1)"

Thanks Shawn,

The website link is indeed a very good place to get information about wireless charging.

I was impressed with the depth and breadth of information.  Plus they did answer the question I had about the full power usage to recharge a battery.

I intuitively knew that the current wall wart chargers were not efficient, which was why I questioned the efficacy of the wireless approach.

Now that I can see the benefits, though mostly due to better charging control, so making the change makes sense just from that improvement.

DAB

Hi Victor.... feedback from our engineer is sounds do able.  Let us know your progress....

Hello Shawn,

I've been trying to design a setup last evening, and I encounter the following issue; I'd like to make the charger very small, and I don't see a solution by TI. The BQ2002 or the BQ22440 are both solutions for NiMH charging (and TSSOP8 for BQ22440 is acceptable), but as far as I can detect both these solutions are meant to be the controller of a buck converter topology. What I need for my application is a boost converter with fixed current limit for charging (5V in, 6-9V out @500mA). Of course I can build a current controlled boost converter, but then I would ruin my cells when they're fully charged, I'd like to have proper detection of the end of a charge.

The LTC4010 kind of seems to do what I need, but I guess you'd be more happy with a TI solution.

Any suggestions would be welcome.

need an h bridge solution for my robot, thought i had it made with the drv8829evm but it doesnt seem to be able to provide adequate starting current. need about 10-15 amp rating preferably in a dip package and made by TI. Any suggestions are welcome.

Shane Corbin

Hi Shane,

DRV8432 looks like the most beefy driver chip, with 14A rating (drivers in parallel).

If you have the DRV8829 you could try to do something which voids all warranties but might help you through the startup current, and that is to place a small capacitor over the current measurement resistor. This way small high-current peaks are not measured. Do remember that they DO run through your driver IC!

I once had a problem with a non-TI part that tripped over a <100us current peak. Unfortunately no external current measurement, so I had to look for another driver....

Hi Shane and Victor, yes you are correct the DRV8432 DRV8432 is the best option but we don't have any in DIP packages.

Hi Victor... feedback from our Engineer is "Either you can make a constant current boost and detect the end of charge by monitoring the temperature. Or you can use a boost to raise the voltage and then use a linear NIMH charger (like the BQ2002)."