| Title: | You get surface noise in real life too |
| Notice: | Let's be conformist |
| Moderator: | GOVT02::BARKER |
| Created: | Thu Jul 28 1988 |
| Last Modified: | Mon Jun 02 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 550 |
| Total number of notes: | 3847 |
As the new proud owner of a Linn Karik-III CD player, I'm interested in
what a switched mode power supply actually is. The Karik sports one,
but I don't understand how they differ from normal transformer PSU'S.
Can anyone help me out?
Dave (who loves the Karik already)
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 508.1 | ESBS01::WATSON | And so, it begins.... | Mon Jan 16 1995 18:03 | 11 | |
What was a Karik-II ?
I'm not sure what exactly a switched mode PSU is but its something
about switching voltages at a HF (hence the name). They've not
traditionally been used in Hi-Fi because of all the RF interference.
Rik with Karik(-I)+Numerik
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| 508.2 | CAPNET::GIBIN::WCLARK | Mon Jan 16 1995 18:18 | 18 | ||
A switcher supply is simply as regulated DC supply that is controlled by pulsing current into the output filter using some technique like PWM. To maintain a voltage the switching device is on longer when more current is needed and less when less is needed. The output filter is a relatively long time constant lopass filter that smooths the pulses. The pulsing usually occurs at hundreds of KHz and the main advantage is that the devices doing the current pulses (usually MOSFETS or the like) are either ON or OFF almost instantly so they do not self heat much (higher effeciency). As was mentioned the big problem using them with audio components is keeping the RFI from the switching out of the audio. Probably 99% of the DC suplies for computers are switchers. There is also a class of amplifer that operates the output devices in switch mode. The principle is much like the switcher supply but the lopass filter time constant is much shorter. This is very sophisticated technology and costs a good deal to design and implement properly. Walt | |||||
| 508.3 | Even better than a Karik-II | KERNEL::HOGGAND | Tue Jan 17 1995 10:36 | 13 | |
Rik,
Sorry, that should have been a Karik-III (Karik was the original,
Karik-II is with the new SBS switched mode power supply and Karik-III
is fully surface mount technology).
Frightened to listen to the Karik/Numerik; the bank has already got me
marked for a visit from the boys :-)
Dave
PS: I now have all the B% tapes; will send them.
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| 508.4 | KERNEL::HOGGAND | Tue Jan 17 1995 10:38 | 4 | ||
Thanks Walt, though I admit that it didn't make much sense to me.
Dave.
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| 508.5 | HLDE01::SOEMBA::RIK | Mostly Harmless | Tue Jan 17 1995 12:04 | 17 | |
... in simpler terms, then
a switched-mode power supply is one where the incoming mains is rectified,
converted into AC again, but this time at a frequency of several tens to several
hundreds of kHz, then transformed down and rectified again. A feedback loop
monitors (one of) the output voltage(s) and adjust the converter thingie
(usually called a chopper) as needed. The advantage of all this is a much
smaller (size and weight) transformer for a given amount of power as compared to
an ordinary 50/60Hz iron-core one, less bulky smoothing caps, and higher
efficiency. Computers use this type of supply.
The disadvantage is that they tend to be 'noisy' (electrically), and not exactly
suited to wildly varying loads as you'd find in an end amp, for instance. A CD
player would be a good candidate for using one; with some care the noise problem
can be eliminated.
- Rik -
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