Constant current limiting function in MEAN WELL power supplies

The task of the integrated protection of power supplies is to protect the end device and/or the power supply when the operating conditions of the device or its condition change. For example, when the end device is started or fails, the current consumption may increase, which may cause the power supply to fail or exceed the output power of the power supply, which will prevent the device from entering the operating mode. In this case, the overload protection (OLP) function is triggered.

In the power supplies of the MEAN WELL company, the OLP function is implemented in almost all types. According to the type of implementation, there are two varieties: switching to intermittent power mode (Hiccup) and output current limiting mode (Constant Current Limiting), depending on the topology and purpose of the power supply. As a rule, switching to overload protection mode occurs at 105-150% of the rated power. The easiest way to illustrate the operation of the overload protection function is on a graph:

Modes of operation of switching power supplies

The main mode of operation of power supplies, as a rule (except for LED drivers), is the output voltage stabilization mode (area A on the graph) at various loads – from 0 to the nominal level of current consumption. However, in cases where the load is capacitive or inductive, there is always an inrush current. An example of a capacitive load may be another switching power supply with an input filter at the input (as a rule, these are large capacities). In this case, the inrush current can reach a significant excess from the rated current level for a short period of time (while this capacity is being charged). An example of an inductive load is any device with electric motors in which, at startup, an increased current consumption occurs to unwind the motor.

If the power supply for the load is selected without taking into account the inrush current of the end device, then when the rated power is exceeded (the moment of transition is indicated on the graph), the overload protection mode is switched on. For industrial power supplies, as well as for DIN rail power supplies, the main mode is the output current limiting mode (Constant current limiting) with a limit on the level of stabilization of the output current and the duration of action.

The output current limiting mode (Constant Current Limiting, area B on the graph) is the transfer of the power supply to the output current stabilization mode at the maximum output power level, while the output voltage is reduced. Exiting this mode occurs as an auto-recovery after removing the conditions that caused the overload, for example, the load goes into operating mode. This mode is typical for most power supplies, for example, HRP, HDR, EDR, NDR and others series.

For programmable power supplies of high-power models RSP-2400, RSP-3000, RST-5000, RST–10000, it is possible to select the required overload protection mode with limited output current - followed by disconnecting the power supply after 5 seconds (constant current limiting, shut off after 5 sec), or continuous operation in this mode continuous constant current limiting mode. The mode is selected by installing a jumper on the additional connector of the power supply unit or by installing a DIP switch (if available) – specified according to the specification for the power supply unit.

Setting the jumper for the Constant Current Limiting function using the example of RSP-2400

Warning: Long-term operation of the power supply in overload or short circuit protection mode should be avoided, as this may lead to a shortening of the service life of the power supply or damage to it. Some models of power supplies have a two-level overload or short circuit protection system. So, in the mode of limiting the output current level, the power supply can only stay for a certain preset time, and then the power supply is automatically turned off or switched to intermittent power mode (area C on the operating mode graph).

For advice or clarification of information on MEAN WELL power supplies, please contact us by e-mail Meanwell@chipdip.ru .