How To Choose Power Supply

1. Start by listing the non-manufacturer-specific parameters to create a multi-dimensional virtual space into which a valid specimen will fit.
2. The next step is to select from the available power supplies all those that fit the above parameters.
3. The third step is to eliminate those that will fit all those that are non-preferred in some way.
4. The fourth step is to throw some money at the problem, either in the form of an internal requisition, a purchase order, a credit card, or some hard currency of some sort.
5. The fifth step is to take delivery of the selected equipment.
6. The sixth step is to read the instructions that came with it.
7. The seventh step is to install it in line with the manufacturer's instructions.
8. The eighth step is to connect the remaining circuitry in such a way that all the downstream equipment is correct, free from any faults, and that the power supply is protected against any inadvertent fault that might arise.
9. The ninth step is to energise the thing and enjoy the use of the equipment to which it is connected.
10. The tenth step is to record the selection protocol in some way, so that the next individual that goes along the route has a shorter path to follow.

It's nice to be able to select a standard high-volume production industrial power supply, rather than a special-designed product. These will often be highly refined and very reliable. They'll also be less expensive.

An important aspect when considering the issue of efficiency is, at what load? It's instructive to plot power consumed by the power supply (power in - power out), rather than efficiency (power out /power in). That's because the latter is generally specified at the full load rating, or at a very high load, whereas it's best to choose a high enough power-supply rating so that you're operating at a fraction of the load capability, say no more than 30% or 50%. You'll have to generate your own plots for this, because the manufacturer rarely gives it.

Consider, you may have a variable load, and for a significant fraction of the time you may be at low or standby load power levels. So you want to ask, what's my power supply's minimum consumed power with NO load? The answer may be surprising: often a "high-efficiency" supply may be an absolute current hog at zero or low loads.

What's more, the vaunted "efficiency" parameter has little meaning in this regime. Yet for many applications, such low-power-consumption aspects dominate over short-interval high-load conditions. So you have to consider them.

For example, a motor position servo system ideally should draw little power except when it's rapidly changing its position. And if it's quick, that means the high transient power consumption time should be short, and it'll spend most of it's time sitting doing nothing, waiting to rapidly go to a new position.