cell phone and i-pod charger from lithium battery

[roltex_rohit123]

Yes it is SMPS. You can probably use the same circuit to make both chargers. I am betting it is only a few resistor changes to change the output level. You may even be able to integrate a switch to go between output settings.

well i think i have now designed my first smps circuit, i would like to ask if i could go for a board layout of this circuit.. i'm eager to see it working. i'l take all the components once you approve and get you the final components available here. if the exact mentioned in the circuit are not available the national software gives its alternatives. i'l use them and make the necessary changes also. now only one thing that worries is the cell/battery undervoltage. i have laptop cells with no pcb protection. literature states that the voltage in the circuit should not go below 3 volts (actually 2.7 but since cells are half dead there will be not time in 3.0-2.7v drop) so i wanted to know how could i accomplish that. the IC has low voltage of 2.7 but reference is 1.26v. should there be another circuit for this?

 

[NickS]

well i think i have now designed my first smps circuit, i would like to ask if i could go for a board layout of this circuit..

Are you asking me permission to layout a board? You can do whatever you like. I think you should pick out some connectors first then sure layout the board(place components close to the way the NationalSemi tool recommends and you should be fine).

i'l take all the components once you approve and get you the final components available here. if the exact mentioned in the circuit are not available the national software gives its alternatives. i'l use them and make the necessary changes also.

Get me the final components? I am confused what you are asking, assuming or implying.

now only one thing that worries is the cell/battery undervoltage. i have laptop cells with no pcb protection. literature states that the voltage in the circuit should not go below 3 volts (actually 2.7 but since cells are half dead there will be not time in 3.0-2.7v drop) so i wanted to know how could i accomplish that. the IC has low voltage of 2.7 but reference is 1.26v. should there be another circuit for this?

You should be able to come up with a simple analog circuit to monitor the battery voltage and cut power when it is too low. Perhaps you could gate the batteries with a relay. There are plenty of ways to do this just use your imagination. It would probably be a good idea to finalize this before layout of you board.

 

[(*steve*)]

once you approve

Everyone here helps out of the goodness of their hearts. YOU have to take responsibility for your own actions. Nobody is going to "approve" anything. The best you'll get is "that looks OK to me".

SMPS are not trivial, and I suggest you follow the manufacturers recommendation in terms of design and layout. Even then, unusual things may happen if your use does not correspond with the design assumptions -- even presuming you have not made any errors.

In short, nobody here is going to guarantee your success.

 

[roltex_rohit123]

i need just ' it looks fine'. since i am doing it or the first time i am a bit scary about this. approve to me meant that 'yes you can, the circuit is erro free now'.

 

[roltex_rohit123]

Are you asking me permission to layout a board? You can do whatever you like. I think you should pick out some connectors first then sure layout the board(place components close to the way the NationalSemi tool recommends and you should be fine).


Get me the final components? I am confused what you are asking, assuming or implying.


You should be able to come up with a simple analog circuit to monitor the battery voltage and cut power when it is too low. Perhaps you could gate the batteries with a relay. There are plenty of ways to do this just use your imagination. It would probably be a good idea to finalize this before layout of you board.

actually i think the mosfet is hard to get here. i am thinking of a substitute of it. thats what i mean. if the mosfet is changet may be there could be some changes in the other components too. so i was asking for your help regarding. maybe on 20th i would be going to town to buy the components.

 

[NickS]

MOSFETS should be interchangeable if you are careful about matching certain performance specs.
I would look for something in a similar package with = or better performance in the following categories. And of course it needs to still be the same type n/p

Vds max
Id max
Rds on
Power max