dual nc400 + SMPS1200

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Power draw without the external vref is 28W, with it: 24.4W

Output of the regulator I compared and the nc400 does appear to detect this rail's voltage before deciding to use it or not. There isn't any difference in idle draw with the Vdr supply higher than 16.5VDC. The voltage after the rectifier is 28VDC so am in the process of acquiring a smaller 15VAC transformer to replace the 18VAC 15VA one I'm currently using to reduce the regulator losses. Hypex states a simple unregulated supply should be okay also so I will test and compare with that next.
 
They redesigned the entire softstart circuitry on the new SMPS1200 runs, the SMD side has significant redesign over the "V7" I previously had, they removed the V marker denoting what it is on the silkscreen on the new one.

Thanks for sharing your investigations.

Have you looked into whether component substitutions on the SMPS1200 can provide the needed Vdr?
 
Thanks for sharing your investigations.

Have you looked into whether component substitutions on the SMPS1200 can provide the needed Vdr?

This was something I was looking at, now that I have a dead SMPS1200 to dissect I was more curious how the Vdr was derived. Vdr appears to be derived from the to220 bdx34 darlington at the far right of the board on the heatsink side, opposite of the bridge rectifier side. There are some SMD components underneath this. The voltage is derived from its own unregulated winding which is rectified straight after the SMPS transformer and snakes around the board to the Vdr regular mentioned previously. It looks like some kind of shunt or zener referenced thing. I have powered up this piece on the bench supply, and 15.95V comes off the Vdr supply after the regulator. Did Hypex actually state why the original Vdr supply didn't work?

It's almost like this supply must exist before the actual HV comes up for the nc400 to use it, maybe there is more to this? I have no issues having the nc400 accept the same voltages offboard as long as the supply exists before HV....

Anyone with an SMPS600 able to confirm if the Vdr on theirs comes up before the main HV?
 
I don't plan on touching my new one simply because I want to be able to complain to hypex the moment it has issues after just a few years. However here is the top left of the old vdr circuit. 2 bog standard diodes with a series resistor looks to be the reference. Bottom left of picture isolated vdr supply to regulator visible.
 

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I wrote Hypex, and they recommend not overdriving Vdr, as it will quickly reduce NC400 lifetime.

They were also unable to recommend an SMPS1200 component swap to bring Vdr to target for the amp modules.

Thanks, I have kept Vdr at exactly 16V, with the offboard PSU I was able to get things down to 22-23W idle which amounts to a noticeably cooler case, if that increases the SMPS1200 lifetime significantly then fine by me. Down by about 7 watts.
 
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