Vasile,


The schematic I attached to the original message was just my first
sketch. My final solution is quite different.

I don't know of any good performance MOSFET transistors without the body
diode. The diode is a side-effect of the manufacturing process and would
not be easy to remove without impairing device performance. Even the
chip manufacturer's schematic designs suggest using two back-to-back
MOSFETS for battery chargers, for instance.

Isaac


On 15/03/2015 09:15, embedded systems wrote:
> Isaac,
> Your schematic is nice. However I still not understand why do you need T1
> and T2 when you could use a MOSFET without anti parallel diode for T1
> (charger power .pdf). I'm assuming the VCC does not have the second suppl=
y
> input.
>
> "Transistors T1 and T2 are P-channel MOSFETs with very low Rdson. With bo=
th
> transistors off, current cannot flow in any direction because of the
> face-to-face transistors' body diodes."
>
> thx,
> Vasile
>
> On Thu, Mar 12, 2015 at 2:31 PM, Isaac Marino Bavaresco <
> isaacbavaresco@yahoo.com.br> wrote:
>
>> I just checked my schematic and found that I used the LTC4088 together
>> with an RT6150A and a PAM2401.
>> That was the most economical solution I found. A single-chip solution
>> from LT would be more expensive, so I used one step-up (PAM2401) and one
>> buck-boost (RT6150A).
>>
>>
>> Cheers,
>>
>> Isaac
>>
>>
>> On 12/03/2015 00:11, Isaac Marino Bavaresco wrote:
>>> That's what my circuit does, using the same button for powering-up and
>>> for input.
>>> The switch feeds the bases of two transistors with emitters to ground,
>>> one collector goes to the power circuit and the other collector goes to
>>> a MCU pin. A third transistor is operated by a GPIO of the MCU and its
>>> collector is tied in parallel with the other transistor that commands
>>> the power circuit.
>>>
>>> I use also an RC circuit coming from the external power input that
>>> generates a pulse and turns on the circuit when external power is first
>>> applied but allows the circuit to power itself off afterwards.
>>>
>>> For the buck-boost, Linear Technology has some nice battery management
>>> chips (with what they call "PowerPath") with battery charger and severa=
l
>>> boost and buck-boost circuits. I used one of them, don't remember right
>>> now exactly which one.
>>>
>>> Check the LTC3566.
>>>
>>>
>>> Cheers,
>>>
>>> Isaac
>>>
>>>
>>>
>>> On 11/03/2015 22:52, Lee Mulvogue wrote:
>>>> Just been going back through Isaac's thread from 23/Feb as I'm looking
>> at
>>>> something similar
>>>>
>> http://www.piclist.com/techref/postbot.asp?by=3Dthread&id=3D%5BEE%5D+Cha=
rger+and+power+circuit+for+mobile+equipmen&w=3Dbody&tgt=3Dpost&at=3D2015012=
3104616a#104616a
>>>> and have a couple of related questions;
>>>>
>>>> - if using a momentary button, switching to ground, to latch the power
>>>> supply (MCU holding it there), is it possible to re-use that button fo=
r
>>>> input purposes?  I currently have two buttons switching to ground used
>> as
>>>> inputs, but no latched power system.  I'd like to disable the buck-boo=
st
>>>> on complete shutdown, but don't have room for additional switches, and
>>>> double-pole switches of the style I'm using/need don't seem to exist.
>>>>
>>>> - what type of diodes were D1, D2, D3?
>>>>
>>>> - if I always need both 3.3V and 5V from a li-ion when in operation,
>> with
>>>> the ability to boost from a min of about 3.0V, is there much benefit t=
o
>>>> using two buck-boosts, over one buck-boost to 5V and one LDO for the
>> 3.3V?
>>>> Thanks
>>>> Lee
>>>>
>>>
>>
>>
>> --
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