Ultra 550 5vsb Mod with NCP1200

[LDSisHere]

I have been working on this Ultra 550 5vsb mod for quite a while, well before I did the Antec SL-400 mod, but I have had mixed results.

This supply initially started out with a NPN transistor driving the 5vsb but I did not realize it until I accidentally blew it when I put a 1 ohm load on the 5vsb circuit. This made me think that my poor results were due to the fact that I was driving a NPN instead of a FET. So I replaced the NPN with 5A FET and I got better results but they are still not what I expected. This circuit differs from the one I used on the Antec SL-400 in that there is no resistor between the Aux input diode and the Vdd, it is just a wire. The Aux voltage does not rise on this supply like it does on most other supplies. The really crazy part to me is that the 5vsb for this supply is rated at 2.5A so I would think it would do better than the Antec.

Here are the results using the 60K version of the NCP1200.

No load -> Vdd = 11.52 <-> 5vsb = 5.141

10.0 ohm -> Vdd = 11.57 <-> 5vsb = 5.106

5.1 ohm -> Vdd = 11.55 <-> 5vsb = 5.051

3.4 ohm -> Vdd = 11.52 <-> 5vsb = 4.987

2.6 ohm -> Vdd = 11.47 <-> 5vsb = 4.924

2.1 ohm -> Vdd = 11.46 <-> 5vsb = 4.858

[LDSisHere]

Re: Ultra 550 5vsb Mod with NCP1200

Since the 60K version of the NCP1200 was not giving me the results I wanted I decided to try the 100k version. This did make a small improvement. I think the results are good enough that the supply could be used in a PC with this arrangement but I still think I am missing something.

Anyway here are the results:

No load -> Vdd = 11.72 <-> 5vsb = 5.141

10.0 ohm -> Vdd = 11.59 <-> 5vsb = 5.106

5.1 ohm -> Vdd = 11.49 <-> 5vsb = 5.054

3.4 ohm -> Vdd = 11.45 <-> 5vsb = 5.010

2.6 ohm -> Vdd = 11.52 <-> 5vsb = 4.956

2.1 ohm -> Vdd = 11.49 <-> 5vsb = 4.905