Hello, guys!

Recently, I've been facing issue on dimming LED drivers from Diodes Incorporated. As example, the LED drivers I'm in trouble with is: AL8843SP.

On datasheet, the manufacturer says CTRL pin must be drive with: open drain output or push pull output stage. I build those circuits, but none of them seems reliably to drive that pin. In one way, or another, when I put all in test, the integrated circuit (AL8843SP) does not work properly and end up to fail.

If any one can help me, indicating a proper circuit (bulletproof) to driver CTRL pin, I'll be very grateful.

Thank you very much!

 

Hello, guys!

Recently, I've been facing issue on dimming LED drivers from Diodes Incorporated. As example, the LED drivers I'm in trouble with is: AL8843SP.

On datasheet, the manufacturer says CTRL pin must be drive with: open drain output or push pull output stage. I build those circuits, but none of them seems reliably to drive that pin. In one way, or another, when I put all in test, the integrated circuit (AL8843SP) does not work properly and end up to fail.

If any one can help me, indicating a proper circuit (bulletproof) to driver CTRL pin, I'll be very grateful.

Thank you very much!

What voltage are you driving the CTRL input with? Not higher than TTL level I hope!

 

What voltage are you driving the CTRL input with? Not higher than TTL level I hope!

Hi, Sarah!
I'm driving the the CTRL pin within the specifications.
I would like to make a protection circuit, that is, something robust that will ensure reliability!

 

Hi, folks!
Just to point it out, the circuit I made to drive the CTRL pin was as follow:



On input voltage, I have +24Vdc that is lowered to +3Vdc to drive CTRL pin when dimming is not in use.
When I start to dimming (0-5Vdc), Q1 (JFET) stops to conduct, showing +3Vdc on CTRL pin.
That circuit works on first glance, but something happens, that I don’t know, and IC presents improper work.
Can anyone help me?
Thanks!

 

Hi, folks!
Just to point it out, the circuit I made to drive the CTRL pin was as follow:

View attachment 310032

On input voltage, I have +24Vdc that is lowered to +3Vdc to drive CTRL pin when dimming is not in use.
When I start to dimming (0-5Vdc), Q1 (JFET) stops to conduct, showing +3Vdc on CTRL pin.
That circuit works on first glance, but something happens, that I don’t know, and IC presents improper work.
Can anyone help me?
Thanks!

What is driving the JFET?
As long as the LOW voltage is below 0.3V, it should be fine to use a CMOS output device to drive the CTRL pin, even if this goes to +5V.
I'd get rid of the JFET and drive it directly from the 0-5V modulation signal!

 

What is driving the JFET?
As long as the LOW voltage is below 0.3V, it should be fine to use a CMOS output device to drive the CTRL pin, even if this goes to +5V.
I'd get rid of the JFET and drive it directly from the 0-5V modulation signal!

Hi, Sarah!
Thanks for reply!
Drive the CTRL pin direct from CMOS, or PWM signal, is even worse and unreliable!
Doing that I've experienced bad results too.
Thanks!

 

Hi, Sarah!
Thanks for reply!
Drive the CTRL pin direct from CMOS, or PWM signal, is even worse and unreliable!
Doing that I've experienced bad results too.
Thanks!

Can you show us your full circuit, and your PCB layout?