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Power Supply Engineer - Noise Test of Module Power Supply in Circuit Design



Power Supply Engineer - Noise Test of Module Power Supply in Circuit Design

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With the integration and standardization of the module power supply design, its power density rises linearly, while the module power supply becomes smaller and smaller. This makes the various interference tests of the module power supply begin to become important. In this article, Xiaobian will introduce the noise test method for module power supply and introduce it.
The noise test of the power module is mainly divided into three points.
Test Conditions
The module power supply AC input voltage is 220V, and the output is fully loaded (for multiple outputs, each channel is fully loaded). The AC input voltage can be set to 90V, 220V, 265V as required, and tested under full load output conditions.
Test Methods
During the test, the oscilloscope TIME/DIV is set to 10uS/div, and the bandwidth is set to 20MHz. The peak-to-peak value of the output voltage displayed by the oscilloscope is the output ripple voltage (peak-to-peak including glitch is ripple+noise).
1) The input voltage of the module power supply is adjusted to the nominal voltage, and the output current is adjusted to the rated current.
2) Module power supply ripple is usually expressed in terms of peak-to-peak. The main test method.
The module power supply ripple and noise are AC components superimposed on the DC output voltage. Ripple and noise are measured at rated load and ambient temperature. For a switched AC/DC module power supply, the output ripple voltage is a small pulse of a system with high frequency components, so the peak-to-peak value is usually measured instead of the effective value (RMS). Its measured value is expressed in millivolt peak-to-peak (mVp-p). For example, when the peak-to-peak ripple of an AC/DC module power supply is 50mV, its RMS value is very low, only 5mV, but whether it can be used in a certain system must be further considered.
Because of the high frequency components contained in the measured ripple, special measurement techniques must be used to obtain the correct measurement results. To measure all high frequency harmonics in the ripple spike, an oscilloscope with a 20MHz bandwidth is typically used.
Secondly, when performing ripple measurements, great care must be taken to prevent false signals from being introduced into the test equipment. The probe ground clamp must be removed during measurement because in a high frequency radiation field, the ground clamp will accept noise like an antenna, interfering with the measurement results. Use a measurement method with a probe with a grounding ring to eliminate interference.
A method of measuring the ripple output voltage of a module's power supply using a 50Ω coaxial cable. The coaxial cable is directly connected to the oscilloscope. To reduce noise, an aluminum or copper ground plate should be used for the measurement. The measured value is 1/2 of the actual value.
Another method of measurement using double lines.
Place the module power supply at a location 25 mm above the ground plane. The ground plane consists of aluminum or copper. The output common terminal of the module power supply and the AC input ground are directly connected to the grounding plate. The grounding wire should be thick and not longer than 50mm.
Use a 16AWG copper wire to make a 300mm long twisted pair, one end connected to the power supply output, the other end connected in parallel with a 47μF tantalum capacitor, and then connected to the oscilloscope. The lead of the capacitor should be as short as possible. Note that the polarity should not be reversed. The “ground” of the oscilloscope probe should be connected to the ground wire as much as possible. The oscilloscope bandwidth should be no less than 50MHz, and the oscilloscope itself should be grounded.
Output noise test (divided into peak-to-peak noise, telephone weight noise, broadband noise, discrete noise).
At present, the main suppliers of module power supply in the domestic market are Aipu Electronics, VICOR, ASTEC, LAMBDA, ERICCSON and POWER-ONE. Since the types, series, and specifications of module power supplies produced by various companies are difficult to count, their functional characteristics and physical characteristics are not the same.
Therefore, it also determines that different module power supplies are also slightly different in terms of maintenance and installation. And in the large-scale use of semiconductor and packaging technology, module power supply must develop toward high density and high efficiency, and in application design, it will become more and more simple.
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