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Issue with LM3409

Other Parts Discussed in Thread: LM3409

hello Folks,

We are facing lots of issues with LM3409 and I need your help in resolving them ASAP. I had listed the problem below:

 

1)Noise: The device is producing erring noise the moment we switch on the PWM. I hope it's due to the ripple current. We are varying current from few mA to 650 mA. So please suggest me a method to avoid this noise.

 

2)Issues with parallel dimming using single LM3409: We are having single string of two type of LEDs, 4 white and one orange. We had connected one mosfet across 4 white led and one across one orange leds. We had          tested the parallel       dimming in four scenario. In all this scenario we kept the enable pin high.

 Thanks,
srijan

    a)We had started from OFF condition of the both orange and white led. Slowly started reducing the PWM to MOSFET across orange led and observed the orange LED brightness change. The change is abrupt and we are not able get a smooth transition from no brightens to full brightness. Once the orange LED become completely ON/full brightness we started reducing the PWM to MOSFET across white LEDs. The change is smooth and we got the smooth transition from no brightness to full brightness.

 

  b)We had started from OFF condition of the both orange and white led. Slowly started reducing the PWM to MOSFET across white led and observed the white LED brightness change. The change is abrupt and we are not able get a smooth transition from no brightens to full brightness. Once the white LED become completely ON/full brightness we started reducing the PWM to MOSFET across orange LED. The change is smooth and we got the smooth transition from no brightness to full brightness.

 

c)We had started from ON condition of the both orange and white led. Slowly started increasing the PWM to MOSFET across white led and observed the white LED brightness change. The change is smooth and we are able get a smooth transition from full brightens to no brightness. Once the white LED become completely OFF/no brightness we started increasing the PWM to MOSFET across orange LED. The change is abrupt and we are not able get the smooth transition from full brightness to no brightness.

 

d)We had started from ON condition of the both orange and white led. Slowly started increasing the PWM to MOSFET across orange led and observed the orange LED brightness change. The change is smooth and we are able get a smooth transition from full brightens to no brightness. Once the orange LED become completely OFF/no brightness we started increasing the PWM to MOSFET across white LED. The change is abrupt and we are not able get the smooth transition from full brightness to no brightness

 

3)Issues with parallel dimming using two LM3409: Here we got smooth transition but the LED start flicker when we reach 40% of the PWM.

 

PS: The operating frequency of PWM wave is 1.33KHz, we tried with 600Hz also, but the results are same.

 

The internal PWM of the LM3409 gives a smooth transition that we want, but again here the noise is creating a big trouble.