Question on LM3406HV vs. LM3404HV -- Setting Forward Current

user5280796

Other Parts Discussed in Thread: LM3406HV

Hello, Everybody.

I designed LED Driver with LM3406HV, Input voltage 48V, the output voltage 45V, and out current 750mA
But this circuit doesn't work. it generates the output voltage 10V.
What's the mistake?

I hope someone teaches me.

Thank you.

over 7 years ago

0 Irwin Nederbragt over 7 years ago

TI__Mastermind 28655 points

Hello,

That is going to run at a fairly high duty cycle. Can you try making the output a lower voltage or the input a higher voltage. You may be running into the minimum off time.

Regards,

0 user5280796 over 7 years ago in reply to Irwin Nederbragt

Prodigy 50 points

Thank you for response.

I have to make the driver with Input 48V, output 40V and PWM control.
How about to change the Inductor from 33uH to 33mH?
it is possible, isn't it?
Thank you.

0 Irwin Nederbragt over 7 years ago in reply to user5280796

TI__Mastermind 28655 points

Hello,

When the input and output are that close together, 48VDC and 45VDC the off time becomes short. Is your output 45 VDC or 40 VDC. You can look at the switching waveform and see. Making the inductor larger reduces the ripple but Ron will need to change as well.

Regards,

0 Irwin Nederbragt over 7 years ago in reply to Irwin Nederbragt

TI__Mastermind 28655 points

You can change the inductor from 33 uH to 33 mH but it would be better to design the LED driver to know what it's going to do, that is 1000 times greater inductance and not needed.
Did you look at the switching waveform?
Did you try lowering the LED stack voltage or increasing the input voltage?

Regards,

0 user5280796 over 7 years ago in reply to Irwin Nederbragt

Prodigy 50 points

Thank you.
The device can not increase the input voltage. and out voltage can be 35voltge.
The waveform is very disturbing.
In case of change the inductor with 68uH, out voltage was 15V.

perhaps. The circuit seems to be wrong.

thank you.

Power management

Power management forum

Question on LM3406HV vs. LM3404HV -- Setting Forward Current