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
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.