We've been using an HBB5-3-OV-A+G power supply in our rack mount products. One output powers a small fan, and the other powers our product which is an assortment of digital and rf boards and an LCD. It's a 3 amp supply, and our boards and display draw about 1 amp total.
Recently we've been having a problem. Occasionally the output that powers our boards cuts out. When we disconnect and reconnect the AC line it comes back on. The side that powers the fan stays on.
This sometimes happens even when the rack chassis cover is off, and the unit hasn't been on for long, so it doesn't seem like a thermal protection thing. Some units never do this, some do it several times a day.
The 1 amp current measurement is based on the readout of a bench supply, so it wouldn't indicate any short current spikes. I'll have to find some way to monitor the current on a scope. I can't think of any reason why it would spike, though. There are some relays in the device, but they stay in the same position except when the user enters a command, and it doesn't cut out when they are switched.
So, is there anything nonobvious that can trip a supply's overcurrent or thermal protection?
Best Answer
The specification for the power supply states that the current limiting is "Automatic current limit/foldback". Foldback current limited supplies can cause problems with non-linear loads, especially those that draw substantially constant current. This is because there can be two or more stable operating points, one with the supply in constant voltage mode and one or more with the supply in current limit mode. A brief current spike could 'knock' the supply from one mode to another.
But this is somewhat speculative since we don't know the design of the power supply nor the IV characteristics of your product. It would however be worth trying a constant current limit supply instead.
This is an example of what can happen