longpole001
- 5th August 2013, 05:51
Hi guys ,
i dont use mosfets as much more than nice power switch as yet ,
but have need to use the body diode as a reverse polarity protection in a USB ( 5v supply ) LI Ion charger cct , and would like get some input into the mosfet selection design specs and assumptions i have , so far
Option 1
7057
Option 2
7058
I have not made this cct yet ,but waiting on the charger modules
The chargers are common around the place and use the TP4056 controller.
( a good review here ) http://lygte-info.dk/review/Review%20Charger%20TP4056%20UK.html
Unfortunately this controller has no reverse polarity protection on the output side , ( it does on the input side) so if you put the battery in reverse polarity it fries the charger/ controller chip , so reverse polarity protection is required.
option is to use low resistance on mosfets , using the body diode built into the mosfet ,such that the body diode is orientated in the direction of normal current flow , when looking from the battery to the changer and block the direction of the reverse polarity of incorrectly put in battery.
Also i have need to series the batteries as well as charge them individually to ensure a faster charge rate, and use the existing charger modules , without much additional circuit and costs
I thought of using a Pch as well to isolate for both reverse polarity protection of both outputs of the each module , but thought it not required ??? see cct option 2
Also i did not see a reason to isolate the input to the chargers if the power switch was on , as the chargers have current limiting , also the drain for this cct when on is less than 1A
Mosfet Selection
The choice of mosfets were based on following
Common requirements
1. Low On resistance at a voltage min of 10v
2. 1A or greater drain current ability
3. Low gate on voltage of less than 2v , ( so battery will still charge)
4. Body diode reverse voltage of min 10v
5. smd size
6. price , availability - no point buying chargers at $2 and paying $6 for mosfet polarity protection
N channel - Q2, Q4
http://www.nxp.com/documents/data_sheet/PMV30UN.pdf
P channel - Q1,Q3
http://www.farnell.com/datasheets/1698603.pdf
any comments on my planned cct on my mosfet selection or the quick design
i dont use mosfets as much more than nice power switch as yet ,
but have need to use the body diode as a reverse polarity protection in a USB ( 5v supply ) LI Ion charger cct , and would like get some input into the mosfet selection design specs and assumptions i have , so far
Option 1
7057
Option 2
7058
I have not made this cct yet ,but waiting on the charger modules
The chargers are common around the place and use the TP4056 controller.
( a good review here ) http://lygte-info.dk/review/Review%20Charger%20TP4056%20UK.html
Unfortunately this controller has no reverse polarity protection on the output side , ( it does on the input side) so if you put the battery in reverse polarity it fries the charger/ controller chip , so reverse polarity protection is required.
option is to use low resistance on mosfets , using the body diode built into the mosfet ,such that the body diode is orientated in the direction of normal current flow , when looking from the battery to the changer and block the direction of the reverse polarity of incorrectly put in battery.
Also i have need to series the batteries as well as charge them individually to ensure a faster charge rate, and use the existing charger modules , without much additional circuit and costs
I thought of using a Pch as well to isolate for both reverse polarity protection of both outputs of the each module , but thought it not required ??? see cct option 2
Also i did not see a reason to isolate the input to the chargers if the power switch was on , as the chargers have current limiting , also the drain for this cct when on is less than 1A
Mosfet Selection
The choice of mosfets were based on following
Common requirements
1. Low On resistance at a voltage min of 10v
2. 1A or greater drain current ability
3. Low gate on voltage of less than 2v , ( so battery will still charge)
4. Body diode reverse voltage of min 10v
5. smd size
6. price , availability - no point buying chargers at $2 and paying $6 for mosfet polarity protection
N channel - Q2, Q4
http://www.nxp.com/documents/data_sheet/PMV30UN.pdf
P channel - Q1,Q3
http://www.farnell.com/datasheets/1698603.pdf
any comments on my planned cct on my mosfet selection or the quick design