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Why noise output from choke?
Why the output choke got noise sound when the 3D mark running?
The reason is the loading change frequency between 50Hz and 20KHz,
The core and wire of coke will vibrate by loading change frequency, the noise of choke will follow the frequency , and the loading change level will change the noise dB.
If the vibration frequency out of this range or the noise less 10 dB, we can't hear it.
Many M/B got same result,
When vibration noise happen on transient or loading change only,
And the thermal of choke never getting hot , it's normal.
On the static load, the choke should silence.
If on the static load , the choke got noise and also getting hot, that's abnormal.
Poor the gain of feedback and poor transient response also can reduce the noise.
Like slow down the switching frequency , reduce the gain of compensation, or use slowly response time, it will help to reduce the noise. But the change will impact to the transient result.
For example : when the loading be changed by 50A/us, the output choke follow by 10A/us, it's need 5 us to got the change.
If output can follow fast than 50A/us, than the change time will short and the vibration will heavy , the noise dB will increase .
Increase switching frequency, change the vibration frequency some times reduce the noise, But the change will impact to the thermal of Upper Mosfet.
Summary:
The choke silence on static load, thermal stable on static and loading change, getting noise from loading transient, It's mean normal. Nothing change recommend.
If the noise is not acceptable by customer, a little lower switching frequency will smaller impact to transient and improve the thermal of high side Mosfet.
But the change doesn't mean the noise will be gone, some loading c frequency change or heavy current change slew rate, the noise will possible happen again. |
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狗仔卡
发表于 2005-10-10 12:20:00
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