FREQUENTLY ASKED QUESTIONS

When purchasing a power supply, the first choice to be made is linear supply or switching supply. Linear power supplies offer low ripple and noise specifications and have fast transient behavior. However they are inefficient and generate a lot of heat. They are also quite heavy. As a result most engineers prefer linear power supplies for low power applications. Using switching power supplies is a better choice for higher output power or multichannel applications. They provide higher power density. Switching power supplies are easier to control than linear supplies and cost about the same per channel.

Transient response is a measure of how well a power supply copes with changes in current demand or how well the supply follows the changes in the load impedance. This is an important specification for many applications.

DC output voltage slew rate is a rise or fall time. DC programmable power supplies have output filters that use large capacitors that store a lot of energy. It’s mainly the charge and discharge time of this filter, combined with the current demand of the DUT, which determine a supply’s voltage slew rate. The voltage slew rate is mostly independent of the connected EUT.

Load Regulation is an important specification of programmable power supplies. This means some percent output voltage change from its set-point due to a change in the current demand of the EUT. Normally this effect should be very small, less than 0.01% of set output voltage.

Line regulation specifies the percent change of the DC output voltage or current as a function of AC input line voltage. This specification is important when the input line voltage is not stable.

Stability is a measure of a supply’s long term output voltage or current drift. Stability is primarily specified in parts per million or ppm.

If more output current is required then paralleling power supply outputs is generally the solution. Ametek Programmable Power uses a dedicated control bus to connect its power supplies in parallel. The system configures itself automatically, identifying which unit is the master and which units are the slaves.

If more output voltage is required then connecting power supplies outputs in series is generally the solution. All you have to do is to connect the positive terminal of one supply to the negative of another. The limitation is that when operated in series, there are no master and slave units. Individual power supplies has to be programmed.

DC programmable power supplies typically provide a standard and isolated analog interface. Through the analog interface a supply’s DC output voltage, current and over voltage protection can be set. The control signal can be a voltage signal, a current signal or by connecting a resistor to the analog input.

Many DC programmable power supplies can be configured for either local or remote sensing. For a more accurate output voltage setting, remote sensing should be use. This method compensates for the voltage drop across the leads to the load terminals.