Antec SL-400 5vsb Mod with NCP1200

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

I finally was able to give this project some attention again last night.

Due to an intolerable ringing, I pulled the 0.24 ohm current sense resistor that I had previously tried and replaced it with a 0.75 ohm resistor. I also pulled the 5N60C FET and replaced it with a 7N65C.

I resumed my 5vsb testing at the same point I had stopped, which was a 1.3 ohm load. Previously the voltage quickly started dropping at this load which, at Everell's suggestion, was the reason for lowering the value of the current sense resistor.

I still had a slight ringing but it was much less than with the 0.24 ohm current sense resistor. I noticed that the ringing seemed to stop after the supply warmed up under the 1.3 ohm load. I ran the supply for 1 hour at this load. The 5vsb was steady at 4.94V for the duration of the hour.

I then tried adding another load resistor taking the load down to 1.1 ohms. It ran fine when I turned it on and it was still above 4.9V. While these load tests are running off to the side of me I usually work on other projects, which was the case last night. After about five minutes, I looked over and the 5vsb voltage was slightly above 0V. As I went to turn off the power to the supply I could smell something burning.

I have not yet had a chance to see what died, but I suspect it was the diode on the output of the 5vsb transformer since Everell had a similar experience with his experiment.

[ben7]

Re: Antec SL-400 5vsb Mod with NCP1200

You had a good idea about the frequency so I put on 100k chip to see if it would help. Unfortunately, it was still squealing very loudly.

I do not have the means to measure the circuit frequency. I have an oscilloscope on my wish list, but it will be a while before I am able to get one.

I will probably order some .75 and .5 ohm resistors to try and see if that makes a difference.

As far as I know, the squealing is from instability (ringing/oscillating) in the circuit. Could be the feedback is not adjusted quite right, and/or the frequency the transformer is switched at could be adding to the problem.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

re:whine

You're running the 60kHz version, yes? Could it be the wrong freq for the circuit?

I'm aware that all the mods for this circuit so far are ~60kHz with the DM311 being the highest at 67kHz.

-but-

Has anyone -measured- the original circuit freq?

My 2¢

T

You had a good idea about the frequency so I put on 100k chip to see if it would help. Unfortunately, it was still squealing very loudly.

I do not have the means to measure the circuit frequency. I have an oscilloscope on my wish list, but it will be a while before I am able to get one.

I will probably order some .75 and .5 ohm resistors to try and see if that makes a difference.

[Toasty]

Re: Antec SL-400 5vsb Mod with NCP1200

re:whine

You're running the 60kHz version, yes? Could it be the wrong freq for the circuit?

I'm aware that all the mods for this circuit so far are ~60kHz with the DM311 being the highest at 67kHz.

-but-

Has anyone -measured- the original circuit freq?

My 2¢

T

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

I got around to changing out the 5vsb current sense resistor last night. It turns out the original one was marked as 1 ohms and actually measured 1.3 ohms on my DMM so it really was 1.1-1.2 ohms. The largest value resistor less than 1 ohm that I could find measured 0.24 ohms on my Blue ESR tester. Using a DMM on a resistor value this low is pointless which is why I turned to the ESR meter.

I did not know what if anything would happen using a value this low as a replacement but since I could not find anything else I decided to go for it. I also went from a FQPF4N60C to a FQPF5N60C for the FET. I wanted to go bigger but I needed a FET with full length leads to reach through the holes and this was the biggest I had on hand that did not have the leads trimmed.

I mentioned in post 2 that I could hear a slight whine from the 5vsb circuit before when it did not have a load. Well, when I turned it on this time there was nothing slight about it. At this point I did not have much time to mess with it or write down numbers but the 5vsb voltage was slightly lower than what I had been seeing previously. I started adding load 10 ohms at at time in parallel all the way down to 2.1 ohms. Each load resistor changed the sound as it was added, but never eliminated it.

I guess the big question is if it will hurt anything to run it like this for testing (if I can stand it) or will it damage something?

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

What kind of setup would I need to measure the efficiency? If I knew how to test it I would try it as long as I already have the tools on hand.

[ben7]

Re: Antec SL-400 5vsb Mod with NCP1200

With the 100k NCP1200 chip the Vdd went down a little, but did the temperature of the transformer go up? That might be the tradeoff.

Also an interesting thing to know would be the efficiency.

[everell]

Re: Antec SL-400 5vsb Mod with NCP1200

I am not sure what the meltdown temperature of the transformer would be. I am not even sure if we will be able to get 5 amps from the 5vsb using a one ohm resistor load. If we can, maybe some manufacturers will be watching and maybe we will start seeing some major improvements in 5vsb technology.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

You have a good point about the transformer temperature, that is something that I need to check along with the voltage going to the UC3844 PWM chip to see how it is affected by the 100k chip. I was using my third meter at the time for other tasks while these tests were running off to the side. I think it is interesting to see the difference the frequency makes on the circuit.

I will hopefully have time to change out the resistor in the near future. As far as pushing the 5vsb transformer, what temperature should be the cutoff to make sure it is not pushed to the meltdown point? Keep in mind the accuracy of the IR thermometer I am using is questionable.

[everell]

Re: Antec SL-400 5vsb Mod with NCP1200

With the 100k NCP1200 chip the Vdd went down a little, but did the temperature of the transformer go up? That might be the tradeoff. As you increase the 5vsb loading even more, you might be looking at transformer "melt down" much sooner than with the 60k chip. We MIGHT even find that the transformer is optimized for 60 khz, that the primary winding and 5vsb winding are right, but the Vdd winding simply has too many windings.

The Vdd winding and its DC voltage going to the 5vsb chip is why I had to be selective as to which chip I used and which chip worked best.

I am looking forward to seeing results when you go to 1.0 ohm loading on the 5vsb output.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

I setup a 60k NCP1200 with a 200 ohm Vdd resistor to match the 100k NCP1200 I had setup previously so that the test results would have less variables involved.

100k chip - NCP1200 - 200 ohm vdd resistor (R2 on my schematics)


No load -> Vdd = 10.33 <-> 5vsb = 5.140

2.1 ohm -> Vdd = 12.84 <-> 5vsb = 5.055

1.7 ohm -> Vdd = 12.99 <-> 5vsb = 5.037

After 1 hour

1.7 ohm -> Vdd = 13.04 <-> 5vsb = 5.038



60k NCP1200 - 200 ohm vdd resistor (R2 on my schematics)


No load -> Vdd = 10.27 <-> 5vsb = 5.141

2.1 ohm -> Vdd = 14.07 <-> 5vsb = 5.056

1.7 ohm -> Vdd = 14.07 <-> 5vsb = 5.038

After 1 hour

1.7 ohm -> Vdd = 14.07 <-> 5vsb = 5.039


The 5vsb output difference between the two is trivial but there is quite a difference on the Vdd. In either case the increased resistor value prevents the Vdd zener's 15V threshold from being reached which I would think is a good for a longer service life of the zener itself.

Below are the results I got with the original 110 ohm Vdd resistor to make it easier to compare the difference between them.



60k NCP1200 - 110 ohm vdd resistor (R2 on my schematics)

No load -> Vdd = 12.55 <-> 5vsb = 5.143

2.1 ohm -> Vdd = 14.88 <-> 5vsb = 5.061

1.7 ohm -> Vdd = 14.89 <-> 5vsb = 5.045

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

The power FET has a low value resistor between source and ground. This resistor develops a voltage which the CS (current sense) on the NCP1200 looks at to determine overcurrent cutoff. It could be that you have arrived at this point. To determine if this circuit will do more, you will need to change this resistor to a lower value. Then retest and hope............



hope that this doesn't happen.

I think the resistor you are referring too measured 2 ohms when I was tracing out the circuit. I now have 1 ohm resistors with choice of 2 or 3 watt ratings to choose from that I could use. I am not sure if the 3 watt will fit but if it will that is what I will use. I have a few other tests that I want to try first.

Tonight, I finished populating a board with the 100K version of the NCP1200, but I only had time to do a quick check of the voltages. I also changed resistor R2 (Vdd) from 110 ohms to 200 ohms to reduce the load the zener has to burn off. This may have not been the best idea for comparison purposes so I will have to make a 60K board with a 200 ohm resistor for a more direct comparison. On my Ultra the 100K chip worked better but for this Antec that may not be the case. I just ran the supply for a few seconds at each setting, I will have to wait until I have more time to do longer tests.


No load -> Vdd = 10.33 <-> 5vsb = 5.140

2.1 ohm -> Vdd = 12.84 <-> 5vsb = 5.055

1.7 ohm -> Vdd = 12.87 <-> 5vsb = 5.037

[everell]

Re: Antec SL-400 5vsb Mod with NCP1200

The power FET has a low value resistor between source and ground. This resistor develops a voltage which the CS (current sense) on the NCP1200 looks at to determine overcurrent cutoff. It could be that you have arrived at this point. To determine if this circuit will do more, you will need to change this resistor to a lower value. Then retest and hope............



hope that this doesn't happen.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

After the 1.5 ohm test, I paused long enough to take a picture of the next resistance reading which was 1.3 ohms. I then turned back on to see what would happen. The 5vsb voltage started dropping almost immediately. I only ran it for ten minutes before stopping the experiment since no good could come from continuing. Check out the pictures to see how the voltage dropped in the short amount of time also look at how much the temperatures jumped.

NCP1200 chip - ten minutes later 85F
Heat Sink (top center)- ten minutes later 93F
Transformer - ten minutes later 160F

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

OK I was did some more testing and I was surprised by the results. This supplies 5vsb is rated for 2A and I ran it for an hour today pulling 3.33A. 5V on a 1.5 ohm load.

NCP1200 chip - Initial Temp 65F -> one hour later 83F
Heat Sink (top center)- Initial Temp 67F -> one hour later 87F
Transformer - Initial Temp 64F -> one hour later 143F

I took some pictures this time, so pay attention to the time on the clock. The 5vsb voltage actually rose some shortly after I turned it on which I attribute to the parts warming up but that is just conjecture based on the fact that it stabilized after a few minutes. I think I reached its' limit with my next test however, but I will put that in another post to keep the pictures separate.

[everell]

Re: Antec SL-400 5vsb Mod with NCP1200

The NCP1200 is fixed frequency.......three different frequencies available. Here is my Antec SmartPower 330 sporting the NCP1200 5vsb mod circuit using the 65 Khz chip. I think most of those two transistors circuits run somewhere close to that frequency.

Under no load it is putting out 5.18 volts. Under 2.5 ohm load it is putting out 4.96 volts. That is good for about 2 amps which is what the power supply spec says on the label.

[ben7]

Re: Antec SL-400 5vsb Mod with NCP1200

You could do other things like play around with the operating frequency, and also try to increase efficiency; if you would like to.

[everell]

Re: Antec SL-400 5vsb Mod with NCP1200

However, the temptation to keep pushing the limits is very great.

Do it!!! If you can fix that ole SL400 once, you can always fix it again.

If you don't push it, you will never know what it could have done. That 5vsb transformer IS replaceable.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

I was able to do some 5vsb testing on this supply today and so far the results look good.

I ran it with a 2.1 ohm load for one hour taking temperatures with my IR temp gun so the true values my vary but at least it is an idea of what it is doing under load.

NCP1200 chip - Initial Temp 68F -> one hour later 78F
Heat Sink (top center)- Initial Temp 68F -> one hour later 80F
Transformer - Initial Temp 66F -> one hour later 119F

I then went directly from this test to a 1.7 ohm load for an hour so there was no cool down.

NCP1200 chip - one hour later 80F
Heat Sink (top center)- one hour later 83F
Transformer - one hour later 128F

This supply is only rated for 2A on the 5vsb so I am leery of pressing it farther. The FET on it is rated for 4A and I really do not care if I blow it or the NCP1200 but I would really be unhappy if I burned up the transformer so I am not sure how much more load I can safely push without risking damage to the transformer. However, the temptation to keep pushing the limits is very great.

[LDSisHere]

Re: Antec SL-400 5vsb Mod with NCP1200

Nice!

Uh, wait... is it me or are R2 and D1 not hooked up properly on the PCB layout?

I think the "silkscreen" is skewing your perspective, the copper is not connected. I am attaching a picture of a populated board that I was experimenting with on a different supply so the 110 ohm resistor is replaced with a wire. (Best picture I have on hand of an etched board.)