LM3421: LM3421 Unloaded voltage is unstable.

Hi Xie,

LM3421 is a current regulator and not a voltage regulator. If there is no load at the output, the voltage will continous to ramp up since there is no current (no load). When the output voltage reaches the over voltage level the regulator will shut down and that is what you are seeing.

Thanks Tuan

Hi Xie,

No the output votlage cannot be controlled to a fixed level if there is no load at the output.  Again, the LM3421 is a current regulator.  The voltage will ramp up until it reaches a the controlled current but being that there is no load there it will never reach the controlled current.  The only thing you can control is the Over-voltage protection level so when the voltage reaches that point it will shut down and restart.

Thanks Tuan 

Hi Xie,

Please use our LED driver web site below to help you choose the right driver for your application. You definition above is quite a range and you'll need to narrow it down some.

www.ti.com/.../overview.html

Thanks Tuan