Isolated input for TPS92551 driver led to control the PWM signal.

Oscar Gomez Fuente

Expert 2060 points

Other Parts Discussed in Thread: TPS92551

Hi,

I need a led driver to control an led of around 30 Watts. I' m going to use two TPS92551 en parallel to get my target of the power.

I need to control the luminous flux with a PWM signal. This signal will be an input to the driver led (TPS92551) but I need to isolate this signal because the HW that is in charge of generating this signal has to be isolated from the power supply of the driver led [LED+ / GND]. The power input to driver leds is 48Vdc.

What do you recommend me for this propouse? My idea is to use an optoisolated IC similar to this schematic:

But then I am going to need a regulator to get 5 Volts to feed the Pull-Up resistors from the power input 48 Vdc. What type of power regulator do you recommend me for this purpose? Is this the best way to get my goal?

Thank you so much. Best Regards.

over 8 years ago

0 Clinton Jensen over 8 years ago

TI__Mastermind 25500 points

If you need isolation an opto-isolator is a good way to go. To generate a 5V rail for this since it is low current the easiest way would be to use a linear regulator. There are integrated linear regulators available (I'm not familiar with the part numbers since I work on switchers) or you can do a simple discrete linear regulator with a FET, a zener, and a resistor to generate 5V.

0 Oscar Gomez Fuente over 8 years ago in reply to Clinton Jensen

Expert 2060 points

According to the block diagram in the datasheet:

It seems to be there is a linear regulator included, then It's probable that the scheme I attached you It's likely to be enough.

What do you think?

0 Clinton Jensen over 8 years ago in reply to Oscar Gomez Fuente

TI__Mastermind 25500 points

There is a current source on the DIM pin so that if it isn't needed it can be left open and pull itself up. I honestly do not know at the moment what that current is, but as long as it pulls up fast enough for you when the optocoupler bjt turns off that should work fine.

0 Oscar Gomez Fuente over 8 years ago in reply to Clinton Jensen

Expert 2060 points

Hi Clinton,

I am going to need the data of the current source, and if it could be possible to use this structure:

Thank you so much. Best regards.

0 Clinton Jensen over 8 years ago in reply to Oscar Gomez Fuente

TI__Mastermind 25500 points

The current source is not trimmed, specified, or tested so it could have significant variation, but on the bench I am measuring 48uA. The way you have it connected above should work fine.

0 Oscar Gomez Fuente over 8 years ago in reply to Clinton Jensen

Expert 2060 points

Hi Clinton,

I've checked out this design and works fine:

Thank you so much, best regards.

Power management

Power management forum

Isolated input for TPS92551 driver led to control the PWM signal.