I'm working on a little MCU controlled LED flashlight.
I have a great problem with it: LED ghosting.
It is starting to appear when the switching frequency goes above only a 100hz
I have search Google in this topic, and I have found information that it is maybe because of the stray capacitance of the common anode line, and resistors from the collector of the transistor to ground can help with this.
I tried it, even very low value resistors didn't make any difference.
I don't have and oscilloscope to check out what is going on exactly.
I even tried to insert a blank frame between each multiplexing but it didn't reduce ghosting, just the overall brightness (as expected).
Maybe the problem is with the code, but i can't find out what it is...
Here is the code:
On the left picture the multiplexing is running at 1Khz(visible ghosting) on the right picture it is multiplexing at a 100Hz ( no visible ghosting , but flickering to human eye)
Thanks for the help in advance!
You don't say what type of Multiplexing you are using.
But I recommend to turn off both anode and cathode side before advancing on to the next row.
Row1 (1ms) off (1uS) row2 (1ms)off (1us)And so on......That will give transistor/mosfets time to clear out and there will not be any over shoots.
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