mbeck@ai.mit.edu (Mark Becker) (08/27/90)
Hello * I have a disk drive with a very loud DC-DC converter. The converter is based on a TL-497 switching regulator and generates -12V from +12V. This circuit uses an inductor in a 'flyback' configuration to generate -12V. The inductor whines at about 13 KHz under load and it's loud. I've traced the circuit and, along with some judicious 'scope probing, determined the inductance to be 100 microhenries. It's wound on a small audio transformer core. Peak current through the inductor is about 3 Amps. (Nice of them: .2 ohm resistor in series w/inductor). I've tried two things to eliminate/reduce the oscillator whine: * Decreased the oscillator capacitor in the TL-497 circuit to increase the frequency past, say, 18 KHz. The output waveform degraded immediately (had a nasty spike in it) and the noise had a Bad Feel to it. * Removed the offending inductor, dunked it in silicone rubber, and re-installed it on short wires (mechanical isolation from the printed-circuit board). That reduced the noise some.. but it's still very loud. I would appreciate hearing from others who have solved this kind of electro-acoustic problem. I'd use an external -12V supply.. but do not know the supply sequencing used in this drive. Mark +-----------------------------------------------+-----------------------+ | Mark Becker | .signature under | | Internet: mbeck@ai.mit.edu | construction | +-----------------------------------------------+-----------------------+
dnl@goanna.cs.rmit.oz.au (David "IGOR" Latter) (08/27/90)
In article <10355@life.ai.mit.edu>, mbeck@ai.mit.edu (Mark Becker) writes:
I have a disk drive with a very loud DC-DC converter. The converter
is based on a TL-497 switching regulator and generates -12V from +12V.
This circuit uses an inductor in a 'flyback' configuration to generate
-12V. The inductor whines at about 13 KHz under load and it's loud.
..........
I've tried two things to eliminate/reduce the oscillator whine:
* Decreased the oscillator capacitor in the TL-497 circuit to
increase the frequency past, say, 18 KHz. The output waveform
degraded immediately (had a nasty spike in it) and the noise had a
Bad Feel to it.
* Removed the offending inductor, dunked it in silicone rubber, and
re-installed it on short wires (mechanical isolation from the
printed-circuit board). That reduced the noise some.. but it's
still very loud.
I would appreciate hearing from others who have solved this kind of
----------------
I service a few tv's and often find that some sets have a rather annoying
15.6 Khz whistle, this is normally due to loose ferite transformer cores,
either the eht transformer or the output stage driver transformer.
When you have more than one transformer (as in tv's) press a plastic rod
on the ferite cores untill you find the offending unit. The solution is
simple, spray the core with some sort of polyurethane, getting as much as
possible down past the windings. This, when dry, locks the ferite core down
stopping the ringing. Some transformers also have a mounting bolt which
can be tightened to stop the noise.
Due to the relatively high frequency, a very large percentage of the adult
population cannot hear any ringing, the rest are driven nuts about it....
Take note if your kids complain about the loud noise in the tv.....
I would have thought that 13 khz was too low, but dont increase the
oscillator freq. too high, as efficiency drops right off.