Power supply test load needed - Page 1
Forum section: electronics / testgear

author: bklein
author_rank: Contributor
timestamp: February 14, 2015, 02:03:34 am
content: I discovered that power adapters with PFC can cause conducted emissions failures as they switch across the PFC threshold. I don't understand how they determine the threshold to begin with but I need to test the adapters and make sure they do not have this issue across their output power capability. So I'm thinking I need to set two load levels at perhaps something .5-1.5A apart and would want to ramp this up from 0A to maxA manually as I watch a spectrum analyzer in a CE setup. Anyone know of a commercial load that does this without requiring a lot of programming? I have a unit built in the 70's that does this but everything now is digital and not friendly to such an application. You can set an alternating differential but can't manually ramp it up and down. I want something that is mass produced - I am capable of making one but I want something I can recommend vendors to purchase.

author: saturation
author_rank: Super Contributor
timestamp: February 17, 2015, 02:28:42 pm
content: Yes, many electronic loads can do this. Look at the BK, Maynuo, Array types reviewed on eevblog. There are some specific spec differences in them but they are all easy to program from the front face for step currents. The question you need to answer is how fast is the transition from 0.5 to 1.5A. There are 2 parts, the programmable rate of change, and the hardware slew rate. e.g. In my $350 Array 3710a each change in current can be programmed in 1 sec steps, but the actual slew rate for the current change in that 1 sec is in the microseconds. And yes, you can manually ramp the current up down on demand and watch the EMI burst from the PSU.http://www.array.sh/yq-3721e.htm

author: bklein
author_rank: Contributor
timestamp: February 17, 2015, 03:57:20 pm
content: Ok I'll look into them further. I'm curious if you see a serious glitch when you manually transition through 3A like i get with the Circuit Specialists 3710 and 3711 models.

author: saturation
author_rank: Super Contributor
timestamp: February 17, 2015, 05:23:15 pm
content: Ohoh, what kind of glitch? I think the Circuit Specialist is the same model as Array, just rebranded. I have not had problems with sweeping current to load a device, but the dial isverysensitive, if you rocker or touch it off angle, it may advance or retreat a digit. When I sweep I keep the numeric values at the lowest resolution, so small changes are made with each adjust to compensate for the dial sensitivity. You can use the keyboard too to reduce the sensitivity and inadvertent adjustments. The desktop software it comes with is barely passable, but works.I have not had the LCD annunciators read incorrectly [ e.g. show 0.1A and load 1.0A], that type of glitch would be catastrophic and would be unacceptable. I had tested it for a while using backup volt and ammeters to insure it worked as spec'd.Quote from: bklein on February 17, 2015, 03:57:20 pm

author: bklein
author_rank: Contributor
timestamp: February 18, 2015, 03:36:37 pm
content: Yeah, the one major bummer about these models is that they seem to do a load circuit switchover as the load is adjusted through 3A. Its just a dropout but messes up a nice ramp load test plot on a scope in roll mode. Another minor thing is that first connect of a source to cc mode will cause an overcurrect to the DUT sometimes.

author: saturation
author_rank: Super Contributor
timestamp: February 19, 2015, 07:48:56 pm
content: Ouch, this is not good. I've not had this happen, I was just testing some USB PSU with just a similar test with the Array, without a scope however. I had the DMM on peak-ave-low mode and it did not record any transients not showed by the Array LCD as I ramped current from 0.5-2.5A. I used the wheel set at 0.01A to avoid sudden jumps due to the jittery control.Quote from: bklein on February 18, 2015, 03:36:37 pm