EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Wannes on August 15, 2013, 01:25:16 pm
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Hello,
I made a controller for a RGB led strip, using 555 PWM circuit.
schematic: https://www.dropbox.com/s/9usml232wdu96r5/Schematic%20RGB%20led%20strip%20controller.JPG (https://www.dropbox.com/s/9usml232wdu96r5/Schematic%20RGB%20led%20strip%20controller.JPG)
If I test each color control, it works as intended. But when i make a color combination, a odd flickering/blinking (fast, visible) appears. If i turn each color to the maximum the flickering disappears.
Please help,
Greetings Wannes
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As a pure guess, I'd say that your power (+12 and 0V) wiring is too thin or is routed in such a way that the LED current is affecting the PWM oscillators supply.
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You probably have problem with interference (the 555 frequencies are slightly different thus the relative phase is shifting) in combination with power supply that can not handle all three colors on at the same time (drops voltage).
Try adding a beefy capacitor to your power supply input.
Or change the design slightly to synchronize the phases of the PWM color channels.
That way while it still suffers from the power supply sagging it will not blink.
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I agree with the others that it sounds like a power supply issue but you might swap the 100nF cap on the trigger and threshold pins to one with a smaller value (22nF or 47nF, for example) to increase the PWM frequency. It is at about 120Hz now--which should be okay--but a higher frequency obviously won't hurt (to a point) and is an easy change to make to see if it is a factor or not.
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Problem Solved!
Thanks for the help.
Solved it by using a different capacitor (pwm freq.) for each color (100 nF 68nF 47 nF),
Wannes