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LED Drivers/LCD Bias
LED Drivers/LCD Bias Forum
LM3405 intensity issue
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.
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.
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