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# Need advice on choosing the best IC for LED driver with 40 Ampere output current

I'm Jurgen from Germany. I'm a LED driver designer and designed LED drivers up to 1kW. Now I face a heavy challenge as follows:

UIN is 10V to 60V DC

IOUT is 40 A; in steps of 0%, 25% (10A), 50% (20A), 75% (30A), 100% (40A).

LED is 3.5V at 40A max.

I checked a lot of drivers, eg. LT8391A or LT3763.

I think, 40A output current is really at the edge of possible single-stage solutions.

My thoughts are to use  a synchrone current controller, and / or 2-stage controller.

Can somebody give me more hints or ideas, about solutions to deliver this huge output current?

Thank you very much!

Jurgen.

• DCR (inductor resistance) sensing or resistor sensing ---> Current measurement with resistor, at  common 50mV sense voltage, would mean at 40A a resistor with 1.25 mR and 2W power loss. A resistor with 2512 size could fit; but 1.25mR is rather uncommon, not available from stock.

• Hi

Apologies for the delay. if you are to use LT3763, you can use a smaller resistor 1mR  then you could use the VCTRL to get your target max current.

Regards,

• Thank you for your suggestion.

Right now, I have used 2x 2.5mR in parallel, and can achive 1.25mR. But I have also added a Potentiometer at the VCTRL, so I can check the lower resistance, too. I like this possibility, because often times, it's not possible to get the necessary resistor values.

Best regards!

Jürgen

• Sir,

I have now my prototype sample boards. According to the calculated values, the board is still working fine. Yet, I use the 10mR resistor to achieve 5 Ampere of output current. Input current control and output current control work as expected.

The temperature at LED temperature measuring point reaches 100 degrees Celsius, therefore I changed the upper resistor from 47kOhm to 56kOhm, the lower resistor is still 470kOhm NTC. (To keep the LED temperature lower than 100 degrees Celsius.)

The 47kOhm logarithmic potentiometer can reduce the overall current flowing through the LED, but (as mentioned in the datasheet) it can not reach lower than 10%. But it's okay.

The point is now, that after I have rotated the potentiometer from Zero ohms to 47 kohms forward and backward, the current does not reach the former high value of 5 Ampere. It reaches only 1 Ampere. After switching off and switching on the power supply, the circuit delivers 5 Ampere again. And if I rotate the potentiometer again, then the maximum current is again 1 Ampere.

So, is it not recommended to use the potentiometer at CTRL1 as output current control? Only for adjusting the output current to the required value?

If so, do you suggest to use the input PWM instead? My output current request is 0%, 25%, 50%, 75% and 100% of nominal current. (Final goal for output current is 40A.)

Thank you very much for your attention and suggestions!

Jürgen Krüger.