[ARC5] Scope photos - Chinese DC-DC converters

[Ben Hall]

Afternoon all,

I bought two of the Chinese DC-DC converters, so I decided to hook up 
and test the second one to see if it had the same "sine wave" like output.

For the record, these are the ones I bought:  <http://r.ebay.com/MfTEUQ>

This first photo is a shot of the output of the converter set at 300 VDC 
and about 10 mA load.  Scope settings - 2 volts per division Y, 2 msec 
per division X.  Here the "sine wave" is of approximately 170 Hz, and 
you can see the higher frequency trash riding on top of it:

<http://www.kd5byb.net/DCDConverter/ChineseDCDC_01.jpg>

The second photo shows a zoomed in section of the "sine wave" so you can 
see the switching pulses.

<http://www.kd5byb.net/DCDConverter/ChineseDCDC_02.jpg>

In this third photo, I was trying to show that the switching pulses ride 
on top of the sine wave:

<http://www.kd5byb.net/DCDConverter/ChineseDCDC_03.jpg>

IMHO, something is goofy with these converters.  The 170 Hz wave in this 
converter and the ~300 Hz wave in the other converter suggests to me 
that something is goofy in the voltage regulator control loop.

I'm going to take one apart to see if I can guess at the schematic. 
Yes, the one chip is marked in Chinese characters so that might be a 
bust, but I suspect I can at least figure out the pin functions.

thanks much and 73,
ben, kd5byb