High Voltage Power Supplies & Safety Information

What is the difference between instantaneous short circuit current and continuous short circuit current?

The output section of a typical high voltage power supply is capacitive, which causes it to store energy. When a short circuit is placed on the output of a supply, the energy stored in the capacitance of the multiplier is discharged. The only limit to the magnitude of short circuit current is the resistance in the series with the discharge circuit. All Spellman supplies have built-in output limiting assemblies that limit the instantaneous discharge current to a limited level. The instantaneous short circuit current is determined by the setting of the output voltage divided by the resistance that is in series with the discharge path. The amount of time this discharge event is present(and its rate of decay) is determined by the amount of capacitance and resistance present in the discharged circuit.

When a short circuit is placed upon the output of a supply, there is an instantaneous short circuit current.

Once the output capacitance has been discharged, additional output current can only come from the power generating circuitry of the power supply itself. To prevent this, the power supply will sense the rise in output current due to this short circuit condition and will automatically cross over into current mode to regulate the output current to the programmed present level.

In summary, the instantaneous short circuit current is a pulse of current that discharges the capacitance of the supply, and the continuous short circuit current is the current limit level set and controlled by the current mode of the power supply.