> On Fri, Jun 17, 2011 at 8:44 PM, V G <
x.solarwind.xKILLspamgmail.com> wrote:
>
>> Hey all,
>>
>> I'm trying to charge (let's say) a single Li ion battery (float charge) to
>> 4.0V.
>>
>> The maximum charge current will be controlled with a BJT (tell me if
>> there's a better way) and so I've been doing some simulations to see if I
>> can actually get 4.0V across the battery this way.
>>
>> Screenshot of simulation:
http://solarwind.byethost7.com/pic4.png
>>
>> I'm pretending that R2 is the battery, gradually increasing its impedance
>> as it's state of charge increases. The voltage across the battery never
>> seems to hit 4.0V. I'm doing another simulation with R2 from 1-100k and that
>> seems to get closer and closer to 4.0V as the current goes to 0 and the
>> BJT's impedance rises rapidly.
>>
>> I can understand that at the beginning, the BJT needs to decrease impedance
>> as R2 increases in order to maintain the overall impedance so that the set
>> amount of current goes through. I don't understand though, why just before
>> 40 ohms on the x axis, the BJT impedance increases again. Shouldn't the BJT
>> try and lower its impedance as much as possible so that the most current can
>> go through (even though the maximum amount allowed by the base current can
>> no longer go through)?
>>
>> What is this minimum impedance and why is it there?
>>
>
> Nobody?