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LM3405 intensity issue

Aditya Ayachit
Prodigy 80 points
Other Parts Discussed in Thread: LM3405, LM317, LM3404

Trying to use LM3405 for driving 1 Watt LED.

Problem is as follows:

The LED intensity is insufficient.

The setup is as follows:

1. Circuit as per shown in the simplified block diagram.

2. EN/DIM pin is connected to the supply directly.

3. The power supply is a lithium ion battery (6000 mAh, 3.7V).

4. D1 = 1N5809

5. D2 = 1N4148

6. L1 = 2.2uH

7.C1 = 10uF

8. C2 = C4 = 1uF

9. R1 = 0.25E ( I know it should be more for 250mA current)

10. C3 = 0.01uF

11. Vboost -Vsw > 2.5 ( actually 3.43V) 

All Capacitors are SMD 1206, except the 10uF one which is 0806.

I have tried doubling the inductance value as well as halved it, no improvement.

The most peculiar thing which i am unable to understand is this:

When I change the Li-Ion battery the intensity changes. So thinking  that the battery could be not providing sufficient current, I connected a 5V LM317 Voltage source. It results in an intensity which is further less than that of battery. I took trials with different batteries (all Lithium Ion, all 3.7V, but from different suppliers). The intensity of the LED I get is different.

LM3405 is suitable for Li-Ion batteries, right?

Look forward for an answer and thanks in advance.

Kind Regards,

Aditya Ayachit 

 

 

 

  • 0
    Expert 1920 points

    1) Try to remove C2 and C4. If this doesn't help, add them again.

    2) Try adding a 120uF or more alumininum capacitor on your input. On the LM3404 when dimming, this is required when drawing power from a SMPS with less cap on the output. The current during dimming is very sudden and the lyt acts as a small energy bank. Did it help? If no, try remove C2 and C4.