The unit is on a side of a table resting on a foam mate. The cable comes from the other side of the table horizontally. The unit is parallel to the antenna and the cable is perpendicular....
we would like to find something to shield those cables, what could it be?, thanks
I don't see why an optocoupler should create that much low frequecy noise that one even can see it.The flicker is visible hence the noise is low frequency. I guess it is coming from the opto coupler.
Is the PWM control feedbacked somehow?
No, the PWM is not control feedbacked....
I have already put some capacitance at the output of the last opamp ( the one which is connected to the driver) and it didn't make it better.
The lamp has been tested without the dimming circuitry being connected and it was a pass.
Do you mean to put a resistor in parallel to a capacitor?
At the lamp side, you will need a BP filter tuned to 400Hz. At least something to remove 50Hz line frequency.
The driver at the lamp side sees 400Hz plus 50Hz line frequency (because you have filtered the RF noise). I guess dimming is working but the flicker is constant (most visible at low setting).
You need to bypass the signal at the lamp end; the modulation input at the lamp is high impedance and is susceptible to noise. Putting a cap and resistor can reduce the noise at the lamp end.
Flicker frequency usually is in the range below 20 or 25Hz. Everything above is considered not to flicker. (But maybe a combination of two higher frequencies may cause a sub harmonic frequency / alias frequency)
Thus I see just two sources of flicker:
* PWM jitter
* DC bus voltage variations
(since the LED just sees the voltage of the DC bus and the timing of the PWM)
This is a complete new situation.The flicker is just visible through a camera
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