Introduction

This board was developed to test a seven output supply under different load conditions to look for noise problems. While using 7 electronic loads could achieve the same thing (maybe better since they would be variable loads) it would cost a lot as well as electronic loads were observed to create their own noise, which is antithetical to trying to determine supply noise. A bunch of resistors and switches will not create unexpected noise.

The different loads are also convenient to see how well the supply maintains regulation. It's not going to be good for load transient testing since switches don't make clean, instantaneous connections.

For those that have a parts bin or will want to build it with different load resistors the blank PCB only is also available for order (under a separate product entry).

More information and the source files are available here.

What we use it for

We use switching supplies due to their efficiency and low cost. For audio applications some switching supplies can be very noisy at certain loads. This fixture makes that type of testing easier.

Not too many people may need to test up to 7 supply outputs at the same time, but if you do this could save a lot of time and effort.

The design is posted for anyone to copy. Making one PCB and ordering parts for one is rarely cost effective so we've put our current leftovers up for sale. If there is interest we will continue to make them available.

It's better than...

A couple of resistors and alligator clips are OK for testing a single supply voltage, it isn't very workable for testing seven outputs at once. We tried...

Details

With the kit's standard values, it's designed to test the follow supply voltages at the same time:

• 3.3 (two different supplies)
  • R = 4.7 ohms
  • R = 10 ohms
• 5
  • R = 4.7 ohms
• +/-5
  • R = 10 ohms
• +/- 15
  • R = 150 ohms

The switches allow for loads of {none | 2R | R | R/2 } when equal valued pairs of resistors are used. You can use two different values to get fancier.

It has other features to help out testing: - Banana jacks for all rails, with ground jacks for the bipolar rails spaced on 3/4" centers - Ability to ground the center point for bipolar rails - LED indicators - Two switches for enabling supplies with remote on - Current sense resistors to measure actual currents.

For full details look at the schematic.

Assembly

The current PCB has holes for vertical power resistors with 5mm lead spacing. Some power resistors come with 7.5mm lead spacing and the leads will need to be bent a little to fit.

The silkscreen indicates the component values, so with that and schematic, assembly should be pretty intuitive. The kit does not have build directions as it's intended for assembly by someone familiar with hardware. The design documents include a 3D PDF (download and open in Acrobat to view 3D) that you can also use to determine where parts go. The schematic PDF allows right clicking on parts to get their details as well. The green LEDs end up being really bright with the values marked so if ordering the full parts kit we'll supply higher value resistors.

The PCB is double sided with 2 oz copper. There is flooded ground plane on both sides, with the analog (bipolar loads) grounds separate from the digital loads. Even with the thermal reliefs on the ground plane connections the heavy copper takes a little extra heat.