0
\$\begingroup\$

I need to drive LEDs in LCD backlighting. My LED are in this circuit:

LEDs circuit:

The backlight needs a current of 700 mA at 9 V. What driver should I use for control? According to the current peak calculation is 1.5A at 5V supply power at 79% efficiency of driver.

Can I use the circuit LD41 from STMicroelectronic?

On board I have the power branches 5V and 24V.

\$\endgroup\$
  • 1
    \$\begingroup\$ 700 mA at 9 V comes out to 1.6 A at 5 V with 79% conversion efficiency. As to what you can use, we have no way of knowing since we have little hint of your capabilities. And no, we're not going to look up "LD41". \$\endgroup\$ – Olin Lathrop Oct 12 '16 at 13:54
  • \$\begingroup\$ STLD41 datasheet: www.st.com/resource/en/datasheet/stld41.pdf If you check the datasheet you can see that it has maximum output current of about 0.12A so no, you can't use it. \$\endgroup\$ – Rohat Kılıç Oct 12 '16 at 14:03
1
\$\begingroup\$

No. You can't use the STLD41. (next time please supply a link or at least a complete part number, not all STM parts start with ST)

As the data on that part clearly states the maximum drive current is 120mA not the 700mA you need. Taking a quick look at the other ST parts in that category none of them are suitable for a single high current string of LEDs. I think you'll need to look at a different manufacturer if you want a switching LED driver.

If you don't mind terrible efficiency you could use an LDO from the 12V rail in a constant current configuration. It would be simple but you'd be looking at >2W dissipated in the LDO so it'll get hot.

\$\endgroup\$
0
\$\begingroup\$

You could use the ST1CC40 from ST. Peak current capacity is 3A and works from 3 to 18V input.

\$\endgroup\$
-1
\$\begingroup\$

Step up or down , Step-Down has lower losses supports 1.5A CC for LEDs with PWM or On/Off enter image description here

\$\endgroup\$
  • \$\begingroup\$ I need a good efficiency. I have searched a lot of manufacturers of LED drivers, but I have not found yet no chip, which I could use. Lots of of chips is divided into multiple string. But interconnection of LEDs in LCD does not influence. I look at you provide solutions. \$\endgroup\$ – Petr Vítek Oct 12 '16 at 14:12
  • 1
    \$\begingroup\$ Hint signup to www.ti.com and use switcher designer online software> enter design parameters, run> choose max efficiency on dial \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 12 '16 at 14:18
  • \$\begingroup\$ Unfortunately I can not use a 5V supply for this circuit. Is manufactured a boost converter with dim pwm that I can use with a 5V supply. It's not decided that we can use 24V supply or not. \$\endgroup\$ – Petr Vítek Oct 12 '16 at 14:39
  • \$\begingroup\$ This uses 24V input \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 12 '16 at 14:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.