cheap way to charge nimh with dt/dt

Anyone have a good way to charge a 10 cell, 12V nimh pack as follows:

- 0.35A to 1.5A charge current (not adjustable, but in that range)

- dt/dt charge termination and overtemp termination

- input voltage 12V

For less than 2$ at 5000 qty say?

AC

$2 Possible for 25000 pcs.

Actually, $1 is possible for 25000 pcs. Can't do ASIC/uC for less than 25K pcs.

Vin = 12VDC???

A boost smps, controller and temp sensor for less than $2.00US@5000 All I can say is...'Those poor workers in asia'. :(

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Indeed, only $10,000 for ASIC alone. So, $25,000 for 25000 is doable.

Nobody said anything about efficiency or the range of that 12V input. I'm thinking of a boost circuit that just uses a free running oscillator of some kind.

The inductor is likely to be the most expensive part in the circuit. The housing and the bare PCB are likely to add up to more than the $2 limit.

A cheap uC with internal temp sensor, an inductor, a MOSFET and a diode may do the trick. Pulsed trickle charge comes for free.

You could make it short circuit protected if you did this:

----- To ADC ! +-----[Battery]----- ! ! ! ! -+--))))))---+--->!-- ! ! !!-+----To ADC --!! !!- ! GND

The micro pulses the MOSFET and trips the ADC just after it switches the MOSFET off. Applying several cooks constants to the ADC measurements, you get the battery voltage.

Pulsing the ADC several times there after would let the micro watch for the inductor current stopping before it turns the MOSFET on again.