Programmable Power Supplies Information
Programmable power supplies are digitally controlled power sources that provide accurate and adjustable levels of voltage, current, and frequency. They include a processor, voltage/current programming circuits, current shunt, and voltage/current read-back circuits. Remote sensing functions compensate for voltage drops in the load leads by providing feedback of the actual voltage at the load. Over-voltage and over-current protection modes are also available. Comparators continuously monitor the output voltage against a program reference value. If the output value exceeds the reference value, a trigger signal is sent to a silicon-controlled rectifier (SCR) across the output, shutting off the source to the load. Most programmable power supplies are subjected to extensive testing and burn-in periods to ensure long-term performance.
Programmable power supplies can provide AC, DC, or both AC and DC outputs. Typically, AC outputs are either single-phase or three-phase. Single-phase power is often used for low voltage applications. Three-phase power is often used with high voltage power supplies. Waveform outputs include sine waves, square waves, and triangular waves. Important AC output specifications include output voltage, voltage accuracy, output frequency, and output current. Important DC output specifications include output voltage, voltage accuracy, current, and power. Apparent power is the product of the root mean square (RMS) current and the RMS voltage of the AC output. Efficiency is the AC output power divided by the input apparent power.
Programmable power supplies are available a variety of special features. Computer interfaces provide remote monitoring and control. Overcurrent protection is internal circuitry that limits or shuts down the current output during overcurrent conditions. Similarly, overvoltage protection limits or shuts down the voltage output during overvoltage conditions. Typically, overvoltage protection is provided for the primary output. Pure sine output produces a very high quality, pure sine waveform output. Short circuit protection may include electronic current limiting and thermal resets with automatic recovery. Temperature-compensated devices balance changes in temperature that can result in undesirable outputs.
Programmable power supplies are used in a variety of automated equipment testing, certification, and calibration applications. Devices that are capable of following complex output profiles are also used in highly specialized applications such as crystal growth and differential thermal analysis (DTA) at high pressures. Some programmable power supplies are modular, board-mounted, or include a floor-standing cabinet. Others are wall-mounted, floor-mounted, or sit on a desktop or shelf. Open-frame and enclosed units are also available. Programmable power supplies can include a serial interface such as general-purpose interface bus (GPIB) as well as integral software.