Programming Speed -- How fast does the output change in response to programming signals

A switchmode power supply always has an output filter (primarily a series L and a parallel C). The capacitor of that LC filter is the output capacitor for the power supply; it has a substantial value in order to reduce the output ripple. That output capacitor, along with the existing preload and load, determines the power supply output voltage slewing capability.

In fast-programmable linear power supplies the output capacitor is removed and therefore fast output voltage slewing can be achieved. Depending on models, the rise and fall times can be in the range of 10 to 100 microseconds. In switchmode programmable power supplies, the rise and fall times can be 1000 times slower (10 to 100 milliseconds), depending on the size of the output capacitor and whether or not a load is present.

Using fast (rapid rise/fall time) Remote Voltage Programming Signals

If the external programming voltage is a very fast signal and the power supply has no load or light load, it is possible to generate a false overvoltage condition that shuts down the power supply output when the output is programmed from a higher value to a lower value. This can happen because with no load or a light load the power supply will discharge its output capacitor very slowly, while the overvoltage reference voltage quickly tracks the output voltage control signal.

Solution. Kepco offers users requiring fast programming signals specially modified versions of the Series RKW Programmable units that have the automatic tracking overvoltage circuit disabled. For further information or help, please contact Kepco Application Engineering for assistance.