Hi to all,
I have an application where I am using a RF RGB LED controller to drive a High Voltage 110Vdc RGB LED Strip.
During my tests, I used a small lenght of the LED strip connected directly to the RF controller and all functions work perfectly using the remote : Colors change, DIM, etc.
The LED Strip controller DIM is a square wave PWM at 2kHz.
For my specific application, the LED strip will be 20m which consumption will surpass the capacity of the controller. I then found an amplifier (Manufactured by XUNATA) to boost the available power to 750W.
My problem is that the DIM function does not pass through the amplifier. I do not have an oscilloscope but I measured 2kHz at the input of the amplifier and 120Hz at the output.
I have reproduced, to the best of my hobbyist knowledge, one input circuit (RED) on EasyEDA. It is attached at the end of this post.
The source of the problem seems to happen at the 817C optocoupler. For some reason, the input (or output) saturates and cannot replicated the 2Khz.
I tried removing competely C5 thinking it was maybe creating a low-pass filter. No effect.
After reading a little about optocouplers, I figured that maybe I needed to play with the CTR ratio.
I tried increasing the opto input current by adding another 51k resistor in parallel with R4. No effect.
I tried decreasing the opto input current by adding another 51k resistor in series with R4. No effect.
I tried increasing the opto output current by adding another 51k resistor in parallel with R5. No effect.
I tried decreasing the opto output current by adding another 51k resistor in series with R5. No effect.
The only thing I found that made an effect, was to apply a 470ohm resistor across C5 in order the reduce the voltage across optocoupler pins 1 & 2 at 0.5V (Instead ov 1V). This has the effect of having a little DIM capability but not on the full range.
One weird thing I cannot explain yet : When DIM is 100% and I change colors, change of color is instant. When I lower the DIM and then change color, even though it does not reflect of the brightness of the LED, it does passes by a "dim" state before changing to the other color for a fraction of a second.
Any suggestions or something I am missing ?
ps. The amplifier states AC110V input/output but the output is really 110Vdc