With the integration and standardization of DC regulated power supply planning, its power density has risen linearly, while the volume of DC regulated power supply is getting smaller and smaller. This makes the interference tests of DC regulated power supplies become important. In this article, the editor will introduce and introduce the noise test method of DC regulated power supply.
The noise test of DC regulated power supply is mainly divided into three points:
The AC input voltage of the DC stabilized power supply 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 according to the requirements, and the test can be performed under full load output conditions.
During the test, the TIME/DIV file of the oscilloscope is set to 10uS/div, the bandwidth is set to 20MHz, and the peak-to-peak value of the output voltage displayed by the oscilloscope is read as the output ripple voltage (the peak-to-peak value including the glitch is ripple + noise).
1) The input voltage of the DC stabilized power supply is adjusted to the nominal voltage, and the output current is adjusted to the rated current.
2) The ripple of DC regulated power supply is generally indicated by peak-to-peak value. The primary test method.
The ripple and noise of the DC regulated power supply are the AC components superimposed on the DC output voltage. The measurement of the ripple and noise is carried out under the rated load and normal temperature. For switching AC/DC DC regulated power supplies, the output ripple voltage is a small pulse with high frequency weight, so it is generally measured peak-to-peak, rather than RMS. The measured value is expressed in millivolts peak-to-peak (mVp-p). For example, when the ripple peak-to-peak value of an AC/DC DC regulated 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 weight contained in the measured ripple, it is necessary to use special measurement techniques to obtain correct measurement results. In order to measure all the high frequency harmonics in the ripple peak, the oscilloscope with 20MHz bandwidth is generally used.
Secondly, when measuring the ripple, it is necessary to pay great attention to avoid introducing wrong signals into the test equipment. It is necessary to remove the probe ground clip when measuring, because in a high-frequency radiation field, the ground clip will withstand noise like an antenna and interfere with the measurement results. Eliminate interference by measuring with a probe with a ground ring.
It is a method to measure the output ripple voltage of a DC regulated power supply by using a 50Ω coaxial cable. The coaxial cable connects directly to the oscilloscope. To reduce noise, an aluminum or copper ground plane should be used for the measurement. The measured value is 1/2 of the actual value.
The measurement method using the double-grained line
Place the DC regulated power supply at a place 25mm above the grounding plate, which is made of aluminum or copper. The output common terminal of the DC regulated power supply and the AC input ground terminal are directly connected to the grounding plate. The grounding wire should be thick and not good at 50mm.
Use 16AWG copper wire to make a 300mm long twisted pair, one end is connected to the power output, the other end is connected in parallel with a 47μF tantalum capacitor, and then connected to the oscilloscope. The leads of the capacitor should be as short as possible, and be careful not to reverse the polarity here. The "ground wire" of the oscilloscope probe should be connected to the ground wire loop as much as possible, the bandwidth of the oscilloscope should not be less than 50MHz, and the AC of the oscilloscope itself should be grounded.
Output noise test (divided into peak-to-peak noise, telephone weighing noise, broadband noise, discrete noise).
At present, the main suppliers of DC regulated power supply in the domestic market are VICOR, ASTEC, LAMBDA, ERICCSON, POWER-ONE and Stable Electronics. Because the types, series and standard types of DC regulated power supplies produced by various companies are innumerable, their functional characteristics and physical characteristics are not the same.