Hi,
I am using the FL5150 (https://www.mouser.ie/datasheet/2/308/FL5150-D-1809472.pdf).
For the DIM Control, it has an internal 10uA current source, which as per their datasheet, can be used with an external potentiometer (0-250k) to adjust the voltage between 0-2.5V). It mentions you can use a 0-10VDC signal through a 4-1 voltage divider.
My issue is; I'll have 2 of these on a circuit board. As I have found, and some users have helped me fix - I can't tie the 'GND's together between each gang. So I have GNDA, GNDB, and the GND of my controller (powered by the IRM-02-3.3).
As such, I have to isolate my signal from the controller to the Dim Control pin on each FL5150. I used an 817C optoisolator, and chose 1k as the load resistor. I chose 10k and 1uF for my RC filter.
Unfortunately, the 1k load resistor caused the FL5150 to cut out; presumably from over current protection (the Vdd pin isn't there to power external circuits; it is there to be used for the DIM Control Mode pin).
So I increased the load resistor to 10k, but this caused a voltage divider with my RC filter, so I moved those values to 100k and 0.1uF. However, the new problem was that the 10uA current was creating 1V at the dim control pin when InA was OFF. I decided to isolate using a LM358 opamp.
This worked, but I also (for reasons I do not understand) had to add a resistor after the opamp - otherwise the FL5150 would crash out between 1-3V signal on the DIM control pin. So, this works;
However, because of the load resistor, the switching speed is a bit slow, which causes a skew in the voltage at low duty. Instead of 1% being the theoretical 50mV, it ends up being ~300mV. The opamp also adds a small voltage offset close to 0V.
Does anyone know of a better way to do this? Different, specialised ICs to look at? Other isolation techniques?
Input signal has to be PWM - I don't have the ability to use I2C or SPI. Just a single pin.
I am using the FL5150 (https://www.mouser.ie/datasheet/2/308/FL5150-D-1809472.pdf).
For the DIM Control, it has an internal 10uA current source, which as per their datasheet, can be used with an external potentiometer (0-250k) to adjust the voltage between 0-2.5V). It mentions you can use a 0-10VDC signal through a 4-1 voltage divider.
My issue is; I'll have 2 of these on a circuit board. As I have found, and some users have helped me fix - I can't tie the 'GND's together between each gang. So I have GNDA, GNDB, and the GND of my controller (powered by the IRM-02-3.3).
As such, I have to isolate my signal from the controller to the Dim Control pin on each FL5150. I used an 817C optoisolator, and chose 1k as the load resistor. I chose 10k and 1uF for my RC filter.
Unfortunately, the 1k load resistor caused the FL5150 to cut out; presumably from over current protection (the Vdd pin isn't there to power external circuits; it is there to be used for the DIM Control Mode pin).
So I increased the load resistor to 10k, but this caused a voltage divider with my RC filter, so I moved those values to 100k and 0.1uF. However, the new problem was that the 10uA current was creating 1V at the dim control pin when InA was OFF. I decided to isolate using a LM358 opamp.
This worked, but I also (for reasons I do not understand) had to add a resistor after the opamp - otherwise the FL5150 would crash out between 1-3V signal on the DIM control pin. So, this works;
However, because of the load resistor, the switching speed is a bit slow, which causes a skew in the voltage at low duty. Instead of 1% being the theoretical 50mV, it ends up being ~300mV. The opamp also adds a small voltage offset close to 0V.
Does anyone know of a better way to do this? Different, specialised ICs to look at? Other isolation techniques?
Input signal has to be PWM - I don't have the ability to use I2C or SPI. Just a single pin.
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