Winsu
Full Member level 3
Hi All,
I have designed a buck converter to power up some LEDs. I have used the IC FL7701MX to design the buck converter. The wattage that the buck converter delivers is about 6W. This IC has also dimming funcionality that I have included in my design. The design seems to work just fine. It delivers the right amout of power/current when working at full power or at dimming level. The application notes for this design includes a PI filter like the one incuded in the below document:
The configuration of the IC is the same than the above document apart for the value of some components to adjust the current needed and apart from the inductor that in my design it is located before the LEDs. My design also inlcudes a PI filter like in the design notes is described ( the values differes a bit from the desing notes).
My design also includes a line filter before the diode bridge.The line filter includes common mode choke, Cx capacitors, Cy capacitors and a RC filter.Below is a drawing where I summarize the whole design.
This design is resting in a metallic housing with a LED PCB.
The problem comes when someone touches with the bare hands any metallic external part of the housing causing that the lamp starts to dim a bit. When the lamp is touched by plastic, wood or something else it works just fine. It seems like the human capacitance /static electric is coupling noise in somehow.
I think the problem is earth related . Initially I had in my design the electrical earth and the metallic earth connected by a link resistor, but I have removed the resistor and the problem has improved a bit but it still persits.
The Cy capacitosr are connected between live/ neutral and electrical earth and their value is 1nf each. My next step would be to removed the Cy capacitor or reduce their value to see if it resolved the issue.
What could I try to eliminate the problem?. What is causing the problem?, is it noise being coupled on the earth lines or somewhere else?, what else could it be? Any help is very welcome?
Thanks,
Winsu
I have designed a buck converter to power up some LEDs. I have used the IC FL7701MX to design the buck converter. The wattage that the buck converter delivers is about 6W. This IC has also dimming funcionality that I have included in my design. The design seems to work just fine. It delivers the right amout of power/current when working at full power or at dimming level. The application notes for this design includes a PI filter like the one incuded in the below document:
The configuration of the IC is the same than the above document apart for the value of some components to adjust the current needed and apart from the inductor that in my design it is located before the LEDs. My design also inlcudes a PI filter like in the design notes is described ( the values differes a bit from the desing notes).
My design also includes a line filter before the diode bridge.The line filter includes common mode choke, Cx capacitors, Cy capacitors and a RC filter.Below is a drawing where I summarize the whole design.
This design is resting in a metallic housing with a LED PCB.
The problem comes when someone touches with the bare hands any metallic external part of the housing causing that the lamp starts to dim a bit. When the lamp is touched by plastic, wood or something else it works just fine. It seems like the human capacitance /static electric is coupling noise in somehow.
I think the problem is earth related . Initially I had in my design the electrical earth and the metallic earth connected by a link resistor, but I have removed the resistor and the problem has improved a bit but it still persits.
The Cy capacitosr are connected between live/ neutral and electrical earth and their value is 1nf each. My next step would be to removed the Cy capacitor or reduce their value to see if it resolved the issue.
What could I try to eliminate the problem?. What is causing the problem?, is it noise being coupled on the earth lines or somewhere else?, what else could it be? Any help is very welcome?
Thanks,
Winsu