China goes RF

Jan Panteltje · 2014-02-23T13:53:45+00:00

Some time ago I bought a 12V 5A adaptor to power my regulated lab supply on ebay, ebay item number 110948131685, about 9$, 2$ shipping. Arrived some time ago, tried it yesterday, and it worked OK..... Left he lab supply on, went to do something else, noticed my analog video camera had huge RG interference hum bands. Thought its supply was defective, replaced it, did not help. tried things, got the scope, 500 kHz all over the place. switched things off, still 500 kHz all over the pace. Suspected some outside source, but then it hit me: That new AC adaptor was still on. Unplugged it,. RF gone. Tried various loads on it, even the slightest load and 500 kHz RF all over the place, VOLTS, yes VOLTS. Held the scope next to the adaptor, WOW, a real long wave transmitter!! Curious, opened it, it has 2 screws hidden behind 2 rubber stops, and decided to draw the circuit diagram. The first thing you notice about this adaptor is that it is extremely light. The reason turns out to be an other almost core-less transformer. very minimal ferrite core. Here is the circuit diagram: Interesting is that they use a MOSFET, The surprising thing is the NTC, have not seen an NTC in the mains since the old Philips tube color TVs... I do not understand D1, it catches only negative pulses, I would expect positive pulses there. The 2 transistors form some sort of SRC, that can get triggered on 'high voltage' or on 'high current' via the MOSFET source resistor. The TL431 is used as reference and voltage level sensor. The Vbe of the NPN is used as current sense threshold. Nothing new here, except China now runs at 500 kHz, interfering with anything and everything in the vicinity, including AM (1 MHz, 1500kHz), or whatever else picks up the RF, and that RF is several watts. These things should be forbidden, Component view, small transformer: PCB view, they did not forget to put a track in between the opto pins, actually found a lose piece of solder too: Bottom view, easily opened: No...

Feb 23, 2014 63 Replies

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Michael A. Terrell 12 years ago

Crappy Equipment.

Chickenshit Electronics.

-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.

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Michael A. Terrell 12 years ago

Cincinnati Electronics.

Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.

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Michael A. Terrell 12 years ago

What power supplies does Harbor Freight sell? The only electronics I've ever seen there was a 1/2W 5% carbon film leaded resistor assortment.

Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.

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krw 12 years ago

Harbor Fright has an entire aisle of electrical stuff. Much of it unlisted and what is, is likely counterfeit.

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