I have seen a design from (I believe) a Spanish designer of a class-D amp without output filter. The voice coil (an inductor) of a woofer connected to the amp was supposedly serving as the filter. In a thread about the amp, one poster pointed out that the entire speaker lead would emit EMI at the oscillation frequency of the amp. If the amp board were located at/on the magnet of the driver, the leads would be very short and this might not be too much of an issue.
<What about the midrange or tweeter?>
if tweeter is piezo, then it is really a problem.
midrange?
You use a single speaker.
Impedance differences between bass speaker and midrange speaker will give different powers.
Midrange speaker will have low volume.
< How do you see hearing? >
You are a native english speaker, you are from U.S.
I'm just learning English
<speaker lead would emit EMI>
Definitely !
So you you do for hobbies.
EMI bigger is a problem ?
if tweeter is piezo, then it is really a problem.
midrange?
You use a single speaker.
Impedance differences between bass speaker and midrange speaker will give different powers.
Midrange speaker will have low volume.
< How do you see hearing? >
You are a native english speaker, you are from U.S.
I'm just learning English
<speaker lead would emit EMI>
Definitely !
So you you do for hobbies.
EMI bigger is a problem ?
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It probably is, in that you are probably operating an illegal radio transmitter if using one.
Check the flag. I'm in EU just like you!
To add as per the others, Class D without filtering is a very very bad idea.
Commercial class D without a filter will not pass CE in Europe or FCC in USA, there is a thread on switcher circuits and EMC issues in this section with a series of articles from the EMC compliance club, written by Keith Armstrong....
But I often see comments like "Its DIY EMC doesn't matter" yes it does EMC and Signal Integrity are the same thing, only on different scales if you don't care about one then you don't care about the other.
But I often see comments like "Its DIY EMC doesn't matter" yes it does EMC and Signal Integrity are the same thing, only on different scales if you don't care about one then you don't care about the other.
How many spread spectrum devices are high power I have only seen ? The lines for the small ones used in phones etc. tend to still have filtering on the output to stop the cable being a nice antenna even if it is just a ferrite.
Spread spectrum just creates a lot of low noise over a wider bandwidth rather than a narrower bandwidth and a higher noise level. They don't have an output filter but noise is still generated and can still be a problems so some form of noise suppression for radiated emission's may still be needed.
Spread spectrum just creates a lot of low noise over a wider bandwidth rather than a narrower bandwidth and a higher noise level. They don't have an output filter but noise is still generated and can still be a problems so some form of noise suppression for radiated emission's may still be needed.
Have a look at this data sheet, note no filter is required for inductive loads only...
http://www.ti.com/lit/ds/symlink/lm4675.pdf
http://www.ti.com/lit/ds/symlink/lm4675.pdf
Spread spectrum does not reduce emissions, despite what that datasheet says. It simply spreads it out, and so gets under the EMC limits. Note, however, that the EMC limits were specified under the assumption that radiation will mainly be on discrete frequencies. Spread spectrum thus satisfies the letter of the law while riding a coach and horses through the spirit of the law. I believe the regs should be updated to include a limit on total emssion power within a broad band from MF up to UHF.
One day someone will die because of emergency services radio failure in a built-up area due to RF smog. Then just maybe something will be done to get rid of all this graffiti/pollution.
One day someone will die because of emergency services radio failure in a built-up area due to RF smog. Then just maybe something will be done to get rid of all this graffiti/pollution.
I have done spread spectrum SMPS's but didn't know until these recent comments that they are doing them for class D, but these were heavily filtered and laid out correctly (which is critical for EMC).
it seems these devices are for low power hand held devices where cost cutting is taken to the next level to keep costs down, I would love to see some put through EMC testing....
As to it getting banned, we still have not shifted OFCOM one iota on power lines communication for Ethernet etc. which has got a special exemption from CE because it is nothing but EMC noise.
it seems these devices are for low power hand held devices where cost cutting is taken to the next level to keep costs down, I would love to see some put through EMC testing....
As to it getting banned, we still have not shifted OFCOM one iota on power lines communication for Ethernet etc. which has got a special exemption from CE because it is nothing but EMC noise.
The device itself may pass EMC tests. Plugging in some headphones will increase RF pollution, but which headphones using which cable? Provided this is something the user does then it counts as an installation problem, not a device problem? Put the appropriate magic words in the manual and the maker is in the clear - and we know how carefully people read the manuals of their phones and MP3s.marce said:
By the way (and only slightly related to this thread) a whole load of fake dental equipment was recently seized in the UK (please, no tooth jokes from our American readers). The importer claimed that he thought that the CE mark carefully applied to all the equipment meant "China Export" - perhaps the factory thought the same? Among others things, a CE mark should mean that the equipment satisfies EU EMC requirements.
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