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need help beefing up op amp current source

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astock

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op amp current source

Hello,

First post here, so here goes..

Attached is a circuit that is fabricated on a 1" board and is used to drive a separate high power LED at 350mA. The problem is that this circuit seems to be very susceptible to damage from momentary transients i.e. with system power removed a 12V cap discharged to the 5V line causes damage (the MAX4230 has a max input of 6V - I know, I know, I should just avoid shorting things :( )

But even brand new and unused driver boards are prone to "leakage", where the LED lights even with zero volts to Vin. It seems to me that there should be some fairly simple ways to make this a bit more robust without sacrificing any of it's ability.

If anyone can either make a few quick suggestions, or point me to good practical circuit references, it would be greatly appreciated.
 

opamp current source

Hi astock,
I think that Source voltage will be 3.5V and not prefect ground, because 350mAmpx 10R = 3.5V, and opamp o/p is may be 4-4.5V So the effective VGS will be less than 3v which is in general required for mosfet to operate,
may be this is reason for irregular functioning,..

try replacing mosfet with transistor 2N2222A or similar ... because transistor need only 0.7V to ON..


all the best.. :)

--Babesh
 

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