I have an electronic load that I want to use to help me with some ATX switch mode power supply repairs. The instructions that came with the load were rather sparse and I haven't found much for my particular situation on the net. The electronic load is a CSI3710A sold by Circuit Specialist. It is a rather inexpensive model and may not have lots of features but I may not need much. I just don't want to damage it or add more damage to the power supplies. I am confused about the Constant Current, Constant Voltage and Constant Resistance Modes and which one to use. When working with a PS that has the +12,+5 and -5 should I tap the +5 or does it matter? Does it matter if the PS is not putting out any voltage or a low voltage would that damage the load? Anything else to watch out for?
Thanks
Electronic – setting up an electronic load
electronic-loadpower supply
Related Solutions
The tone of your question implies that you have little-to-no experience with switching power supply design.
You are going to have an incredibly difficult time if you want to make a transformer with a single primary and sixteen secondaries. The construction of a transformer is often more critical than the hard electrical/magnetic parameters (turns ratio and core material) due to their being so many degrees of freedom (leakage inductances, coupling ratios, copper loss in the windings, interwinding capacitances, etc.).
If the secondaries have to be isolated from the primary, but can be common to each other, you can go with a single secondary winding rated for all the power you need, and use point-of-load converters (bucks or synchronous bucks) to regulate each rail and provide overload protection (to keep one rail from bringing down the entire bus). You can get complete synchronous buck stages in 2mm square packages (a few external parts and you're done.)
If all 16 rails have to be isolated from each other, I'd recommend not using more than four secondaries per transformer (obviously you need four converters). You could go with a flyback converter design, which simplifies the secondaries (no filter inductors needed) and allows for output > input with galvanic isolation. There are many integrated flyback controllers on the market that contain the MOSFET and control circuitry, just wire up some feedback through an opto and away you go.
You (of course) need a properly-designed transformer, so "yes" the turns do matter as well as the actual number of turns used. The number of turns impacts the inductance, peak current and peak flux density of the transformer. A proper transformer design optimizes the number of turns to minimize core and copper losses, and requires a thorough design procedure. There is no 'magic' number, and more is not always better. For a flyback converter, there are more/different constraints, since the transformer has to be designed to store a certain amount of energy.
Your space budget is small. Forget about sinusoidal waveforms. Forget about low frequency operation. You need high-frequency conversion to minimize the space, which (in its simplest form) involves square waves. Of course, there are efficiency tradeoffs with higher frequency operation. (Space doesn't come free.)
It might work, but I would suggest another approach that is open loop and has 8 bit accuracy.
You can implement a discrete version or buy the chip and R/3R precision component.
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Best Answer
For most testing constant current is the easiest mode to use. You can set the current to the appropriate current level and verify the output voltage specification.
Since most loads are current sinks you shouldn't be able to damage it when the supply is putting out low voltages. You could damage the load with too high a voltage but for an ATX power supply this is unlikely. The output stage of most loads consists of power MOSFETs and these typically have breakdown voltages of 20V and above.
Some power supplies have minimum load requirements for the individual outputs. A comprehensive test would load all the outputs at various combinations of min and max loads but you could probably attach the load to one output at a time. Make sure that each of the other outputs has the min load.