Three Types of DC Power Supplies
Because controlled electrical energy is useful in myriad testing situations, the power supply is an exceedingly popular piece of electronic test equipment. Although anything which supplies power — for example, a combustion engine — can be broadly defined as a power supply, we’ll limit our discussion to types of direct current (DC) power supplies that are commonly used for development, maintenance, measurement, and testing.
The constant voltage/constant current power supply, which as the name implies provides constant voltage as well as constant current, is perhaps the most popular variety of power supply. When operating in constant current mode, these power supplies maintain their set current even as the resistance of the load changes. Constant voltage/constant current power supplies frequently have features including remote sensing, master/slave connections, and analog programming (remote programming terminals).
Multiple output power supplies typically have two or three outputs. If you find that you often use multiple voltages while testing, a multiple output power supply is the cost-effective choice. Many users opt for a triple-output power supply which provides one output for digital logic and two outputs for bipolar analog circuitry. Some common features include timed operation, settable voltage limitations, storage registers for up to fifty instrument states, and the ability to connect two channels in parallel or series for higher current or voltage.
Because they are generally used in conjunction with a computer-operated system for production and testing, programmable power supplies are often referred to as “system” power supplies. System power supplies have used a number of computer interfaces in the past, two of which — IEEE-488, or GPIB (general purpose interface bus), and RS-232 serial communications — have been widely used. Ethernet and USB interfaces have also been quite common.
In addition, these power supplies have command languages for sending instructions to the instrument through the digital interface. These languages include proprietary, SCPI (standard commands for programmable instruments), and SCPI-like. The ability to control a programmable power supply via your computer, instead of pushing keys on the instrument’s front panel, makes this type of power supply especially useful when working on complex setups.