EEVblog Electronics Community Forum
Products => Other Equipment & Products => Topic started by: Hydrawerk on June 17, 2016, 01:45:15 am
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I have two very similar LG PC monitors from 2007 and 2006. They have two identical external 12V 3,5A power adapters. One of them broke down and was unrepairable so I bought a new Mean Well GS60A12-P1J 12V 5A switched PSU. It works well and is nice built. It holds together with two screws so it is easy to take a look inside. Photos are here. https://picasaweb.google.com/106264218831814439783/6296602422849096833#
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But there are some 1Vpp spikes on the output. They are about 100ns wide. Is this OK and normal??
The Mean Well GS60A12-P1J PSU was loaded with a 4 ohm power resistor. The measured frequency is often false because the waveform is quite complex.
Please note that the scope was set to AC coupling.
EDIT: Note that the automatic frequency measurement is often not correct on such a complex waveform.
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This is the output of the original LG DVE power supply after capacitors were replaced. There was also a 4 ohm load used. There is quite little noise on the output. Please note that the scope was set to AC coupling.
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The IC used in Mean Well GS60A12-P1J is probably NE1101 from Neo Energy Microelectronics. Their webpage is offline nowadays. www.nem.com.tw (http://www.nem.com.tw)
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Any thoughts, please?
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Well, my LG LCD monitor still works with this Mean Well PSU so I suppose that this noise is OK and normal.
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Looking at the waveform you attached tells you a great deal about the PSU. It appears to be a flyback topology that operates in discontinuous current mode (as expected). The operating frequency is about 66Khz (15us period). The switch "on" time is about 3-4us and the inductor unloads in about 8us. The triangular waveform is due to the output capacitor ESR as the output inductor unloads into it.
If you want the scope image to be cleaner then use a short-wire measurement technique with the spring clip on the probe tip and disconnect the scope probe ground lead. If you have a decent scope probe it'll be shielded all the way to the tip. This will reduce the pick-up of radiated noise tremendously. If you have a Variac you can vary the mains input voltage and see a corresponding variation of the power switch duty cycle.