32V with 200 mA current LED driver IC

Hello John Cummings,

My input (VIN) is between 5 ~ 12V. Do you have some other solution ?

Regards,
Azlum

Hello John,

Thanks for the reply. Could you advise that, how to set desired output voltage ?

My case,

Input:

12V

Output :

32V @ 200mA

Can you provide the reference schematic for above requirements ? Is it availble in WebBench ?

Regards,

Azlum

If you don't need accurate analog dimming or fast PWM dimming the TPS92411 might be a more cost effective solution. It has reference designs close to what you need on the web. There is a 36V output one at 700mA, you could use the same circuit but just adjust the LED current. It may need a little tweaking (like if the 700mA application ripple current is too high for a 200mA app, you would increase the inductor value) but should be close.

Dear John Cummings,

Thanks for the reply.

For LED driver IC, the output voltage will be set automatically according to the LED current. And no need of setting the desired forward voltage (Vf).

In other words, same circuit can be used for 32V @ 200mA, 36V @ 200mA & xxV @ 200mA (different voltage at same current) without changing any discrete components.

My understanding is correct ?

Regards,
Azlum

The concept of LED driver IC is below:-

Same circuit can be used for 12V @ 200mA, 21V @ 200mA & xxV (maximum output voltage) @ 200mA (different voltage at same current) without changing any discrete components unless change the LED current ?

So how is the LED forward voltage (VF) is setting automatically ?

Regards,
Azlum

Dear John Cummings,

Could you share your feedback ?

Regards,

Azlum

Dear John Cummings,

I have connected 6 LEDs series. One LED current is 1A. So the LED string current is 1A since 6 LEDs are connected in series. 

When we look into the equations, there are two parameters:- 

1) Average LED Current. Please let know how Vsns = 100 mV ?

2) Peak LED current.

Here why we need to consider ILIM as 6A even though we didn't connect the LEDs in parallel ?

Also for below configuration what will be the ILIM ?

Above ILED is 25 mA

What will be ILIM ?

Regards,

Azlum

Hi Azlum,

It depends on the input voltage and output voltage relationship if they are in a boost configuration.
For instance, if your input voltage is at 6V and your output voltage is at 36V, the boost ratio is 6.
With such boost ratio, your MOSFET needs to get current 6 x your targeted output current.
Therefore, the ILIM should be set at 6 A.

The above just illustrates an ideal calculations.

In actual designs, you need to get some margin for this current limit.
So, if your boost ratio is at 6 and targeted output current at 1 A, it is suggested to set current limit higher than 6 A (say 6.6 A).

With your 200 mA examples, it also depends on the boost ratio.
I would suggest a current limit of (200 mA x boost ratio + 10 ~ 15% margin).

Best Regards,
Issac.

Dear Issac,

My input is 12V
Output is 32V.
Ratio is 32/12 = 2.66.

ILIM = 200 mA * 2.66 + 15%
= 0.6118 A

My calculation is proper. I guess. Can you confirm ?

Regards,
Azlum