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Current Source and current mirror.

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Lord Loh.

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constant current source 10ua

I am trying to build a current source that could deliver about 800mA current. It is meant for a battery Charger. I simulated the circuit for 70mA. Then I started to look for commercially available Current source ICs. Most ICs supplied not more than 10uA to 10mA. Is a current source of such high current capacity feseable?

And are current current mirroring circuits efficient? The theory says that the current in one branch is equal to the current in the other branch. So to get a 700mA constant current to the load, I have to drain down 700mA current. It seems a waste.

Please help.

Thank you.
 

art of electronics bjt current mirror

Lord Loh. said:
I am trying to build a current source that could deliver about 800mA current. It is meant for a battery Charger. I simulated the circuit for 70mA. Then I started to look for commercially available Current source ICs. Most ICs supplied not more than 10uA to 10mA. Is a current source of such high current capacity feseable?

And are current current mirroring circuits efficient? The theory says that the current in one branch is equal to the current in the other branch. So to get a 700mA constant current to the load, I have to drain down 700mA current. It seems a waste.

Please help.

Thank you.
Click to expand...
hello,
what theory , i think u can use mirror branch with multiplication factor to get the current u want.
 

the current is that case is equal but if u want the current in the mirror branch "2nd branch" to be multiple of the other "original branch" u can use diffrent multiplication factor , in MOS mirrors if m*(W/L) is the aspect ratio of the 2nd branch and W/L is the aspect ratio of the 1st brach , then u get current m*(I) in the 2nd branch , where I is the current in the first branch.
 

Okay, I read this very think in the Art of electronics(AOE) yesterday... Thank you. It think this can also be done by using a high gain transistor to drive the load. In this case we need not use matched transistors.

ICs are supposed to multiply current by increasing the emitter area (written in AOE)

Any way, What is the best way to make a current source?

LM317? Cascode? Current Mirror? Simple BJT-Zener? MOSFET?

I need it to deliver 700mA to 2200mA to charge battries.

Thank you.
 

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