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Topic: Humming 12v halogen bulb - PWM dimmer, Solved (Read 6 times) previous topic - next topic

Grumpy_Mike

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that the faster you turn on/off mosfet, the more EMI your wiring radiate.

True but PWM of any ratio will turn the FET on at the same speed.

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The solution only to place mosfet as close to load(bulb) as possible

No there are lots of solutions to slow the rise time of the current or reduce the radiated emissions with things like ferrites. 

Magician

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that the faster you turn on/off mosfet, the more EMI your wiring radiate.
True but PWM of any ratio will turn the FET on at the same speed.

Yes, PWM duty cycle is not changing speed of the mosfet, but current spikes are higher/bigger for lower duty cycles, as resistance of the filament goes down.  Variation between cold - hot resistance could be in order 10x, consequently EMI would be stronger for low PWM.

Grumpy_Mike

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consequently EMI would be stronger for low PWM.

No not really, the difference in resistance between a just glowing filament and one burning at full brightness is small compared to that of a glowing on and an off.

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