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LED strip PWM

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Mosaic

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Hi All:
I'm using a 20Vds logic level MOSFet capable of about 9A to drivae a 5A 12V LED string with PWM.
Would placing a 50V, 0.1uF X7R SMD cap across the Drain/source be sufficient for bypassing any transients generated by the wiring upon switch off?

Edit: LTSPICE says no, a 1uF is required, but a freewheel diode seems best. Estimating wiring inductance at about 1 uH between LED modules with up to 50 modules.
 
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spec

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Most Helpful Member
Hi All:
I'm using a 20Vds logic level MOSFet capable of about 9A to drivae a 5A 12V LED string with PWM.
Would placing a 50V, 0.1uF X7R SMD cap across the Drain/source be sufficient for bypassing any transients generated by the wiring upon switch off?

Edit: LTSPICE says no, a 1uF is required, but a freewheel diode seems best. Estimating wiring inductance at about 1 uH between LED modules with up to 50 modules.
Hi Mosaic,

Just use a 10A or greater, 24V or higher Schottky diode and decouple the 12V supply line near the MOSFET with a 47UF aluminum electrolytic capacitor in parallel with a 220nF ceramic capacitor or just one 22uF ceramic capacitor. Both ceramic capacitors should be X7R and not surface mount- the bigger the better.

spec
 

Mosaic

Well-Known Member
not quite the same...decouple means to isolate DC from an ac signal....bypass is the opposite.
 
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