Hello,

I want to drive RGB strip using LM3414 with below specification:
So now my question is ?

1. Can we drive LED using 18V Vbat with Current limiting resistor at Anode of LED ?
2. Since led reverse voltage is VREV =5V and we are driving LED with 18V. Will it get damaged when LED is on OFF state ?

Vbat: 18V
IF_LED : 20mA as per datasheet
https://www.mouser.in/datasheet/2/445/155124M173200-1113601.pdf
http://www.ti.com/lit/ds/snvs678f/snvs678f.pdf



Thanks in Advance !!!

 

Since the RGB strip is another board so does Short Circuit protection needed apart from from current limiting resistor in LM3414 ?

 

Discussion still awaiting

 

Hi Mishra,
Patience patience!
The LM3414 is effectively providing a step down voltage conversion the voltage it will actually end up outputting is determined by how much current your LED will take.. (and the resistors used to program the IC).

So in your case, if you set up the circuit shown in the application schematic, with the correct values for your 20mA current, you do not need a limiting resistor.. it will supply the LED with what ever voltage is needed to get 20mA flowing through it.

However as you are only using 20mA in the first place (which is quite small), you could simply use the circuit diagram you have pasted in. Use a resistor to drop the unwanted voltage (18-5)V @ 20mA...

This is of course a bit wasteful as you are just dissipating I^2 R of heat and only delivering 5Vx20mA of useful power to the LED. Hence when you want to be more efficient you use something like the LM3414. Which uses a switching buck regulator configuration to only provide as much voltage as needed to power the LED.

 

Hi pmd34,

Thank for your reply and time.
In my application i have to drive 28 RGB led using LM3414.

So for 28Red Led i will use one LM3414 driver and one for Green and one for Blue.
So i will use 3 LM3414 to drive total 84 leds

So iwill drive 28 parallel Leds using one lm3414 with if=10mA