Most electrical engineers believe they have a good understanding of power supplies because they are relatively simple, single-function DC devices designed to output controlled voltages. However, there is much more to them than this description would suggest. Although a review of a power supply’s specifications should always be a part of the selection process, other characteristics should also be considered.
Investigate the power envelope
The most significant decision is ensuring that sufficient power is available to energize the device under test (DUT). Different types of power supplies have different power envelopes. A power supply with a rectangular power envelope as shown in figure 1a, the most versatile type, allows supplying any current to the load at any voltage level. A supply with multiple rectangular envelopes for multiple ranges (such as the two-rectangular envelope shown in figure 1b), permits higher values of one parameter at the expense of the other parameter, so it can output a higher level of current but at a lower maximum voltage. Supplies that output a hyperbolic envelope offer a more continuous transition than a multi-range power supply, with one parameter inversely proportional to the other – see figure 1c. High power output supplies tend to have multi-range or hyperbolic envelopes.
Figure 1a: Rectangular power supply envelope
Figure 1b: Multi-range output
Figure 1c: Hyperbolic output characteristic. Maximum voltage and current follow a curve