5 W Universal Input Dual Output Isolated TNY266

03-April-2001

8.8 Acoustic Emissions

The power supply was subjected to acoustic emissions measurement.

The worst-case noise was

measured for variations of both AC line and output loading conditions and is presented in Figure. 8.8.1.

The test unit was placed in an anechoic acoustic chamber, with a microphone located approximately 1”

(25 mm) above the transformer (T1). The power supply was oriented in a horizontal position with the

power supply output loaded via an external Kikusui electronic load. The microphone output was fed to an

Audio Precision audio analyzer to provide the measurements shown. The curves shown indicate the

spectral content of the noise generated by the supply once the ANSI-A weighting factor has been applied.

The audio limit line (Figure 8.8.1) visible at +35 dB represents the generally accepted threshold for power

supply audio noise. A discrete audio frequency amplitude was used rather than a dBA value (dBA

represents the whole audio spectrum). Large peaks may not raise the dBA value yet can result in

unacceptable perceived noise.

As a reference, the approximate dBA background noise floor level is 30 dBA. The microphone sensitivity is

such that 20

µP = 0 dB SPL.

Up to a further 20 dB reduction can be expected from the measurement shown, once the power supply is

sealed inside an enclosure.

Audio Precision

04/18/01 10:47:42

FFT SPECTRUM ANALYSIS

-30

+80

-20

-10

+0

+10

+20

+30

+40

+50

+60

+70

d

B

r

A

0

22k

2k

4k

6k

8k

10k

12k

14k

16k

18k

20k

Hz

+35 dB=Audio Noise

Ambient Noise

Page 24 of 32

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