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DC bias in transformer

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AVGresponding:

--- Quote from: Simon on October 11, 2019, 05:41:41 pm ---So you felt the need to resurect a 6 year old thread.... :palm:

--- End quote ---


I've seen worse necros...   ::)

*almost on topic* a colleague once upon a time (in the late 1990s) said he'd heard 'they' (I'm assuming he meant the 'Powers That Be') were thinking of banning SMPS's due to their noisy switching having a deleterious effect on the mains line.
He went on to say "but transformer/rectifier PSU's have noise too, when they pass the zcp and the diodes in the bridge are switching from on to off to on, there's noise!".
I seem to remember saying something along the lines of "yes, that's a good point", while thinking "yes, but the noise frequency is directly related to the transmission line frequency, and so can be filtered easily...".

Given the number of SMPS's running at any given time, and the random frequency and phase, it's likely the noise sum is effectively near enough zero as makes no difference, but it does make you wonder, what would happen if they all synced into phase at the same time...  :scared:

Simon:
rectifiers and smoothing capacitors create plenty of distortion due to poor power factor. SMPS are usually power factor corrected which mens they have to appear as near linear loads. if they are near linear I expect that anf noise has been minimised already.

AVGresponding:
Have you seen the stuff coming out of China recently?

Hell, forget China (in terms of cheap Chinesium crudites anyway), have you seen the power factor on premium consumer goods like a PS4 for example? On standby I see a power factor of 0.02! And yes, I did get the decimal in the right place!

Simon:

--- Quote from: ThickPhilM on October 12, 2019, 04:30:35 pm ---Have you seen the stuff coming out of China recently?

Hell, forget China (in terms of cheap Chinesium crudites anyway), have you seen the power factor on premium consumer goods like a PS4 for example? On standby I see a power factor of 0.02! And yes, I did get the decimal in the right place!

--- End quote ---

how much does it use on standby? what is the power factor during use? Have a look at Dave's latest pair of videos. A dirt cheap LED driver that has 100% ripple to save money but a power factor of over 0.9, the only thing that lets it down is the fact that you can see the flicker caused by the 100% ripple when using a video camera.....

AVGresponding:

--- Quote from: Simon on October 12, 2019, 04:34:12 pm ---
--- Quote from: ThickPhilM on October 12, 2019, 04:30:35 pm ---Have you seen the stuff coming out of China recently?

Hell, forget China (in terms of cheap Chinesium crudites anyway), have you seen the power factor on premium consumer goods like a PS4 for example? On standby I see a power factor of 0.02! And yes, I did get the decimal in the right place!

--- End quote ---

how much does it use on standby? what is the power factor during use? Have a look at Dave's latest pair of videos. A dirt cheap LED driver that has 100% ripple to save money but a power factor of over 0.9, the only thing that lets it down is the fact that you can see the flicker caused by the 100% ripple when using a video camera.....

--- End quote ---


Underlined relevant sections...

That LED driver will have the same affect on the line as a linear PSU; 100Hz.

Think about it.

In point of fact, all the SMPS's I have encountered rectify line current first, therefore their main interference is going to be line f or 2f. Their switching frequency will be less of an effect due to components sitting between the switching transistor(s) and the line, and as I've also pointed out, they are all going to be running at slightly (or more) different frequencies and phases, so the net effect is likely to be effectively zero.

The only consistent factor is the line frequency, insofar as the noise generated by diodes switching on at their thresholds will be at the line f (half wave) and 2f (full wave).

Most of the modern electronics I see has a pretty shit pf, probably a conspiracy to charge us more for our elastic trickery by charging us for apparent power instead of real power (I worked with ferro-resonant transformers for UPSs, so I know a bit about tinkering with power factors).

If it makes you happy, I'll measure the pf of my PS4 next time I turn it on, later tonight most likely.

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