FAQ01995 of Power Controllers FAQ

This is a function that protects the heater and the system by automatically suppressing excessively large inrush current, such as with pure metal heaters.

As shown in Figure 1, ten times the rated current flows when power is applied to pure metal heaters, for which molybdenum and tungsten are typical. (This current cannot be fully suppressed by using a long soft-start time.)

Figure 1 Flow without Constant-current Function

As shown in Figure 2, the constant-current circuit functions to automatically regulate to the current in response to the input signal. Inrush current is suppressed by reducing the ON phase.
(Overcurrent detection will operate and the switching elements will be protected if a large current flows that the constant-current circuit cannot suppress. If this occurs, the input signal will be cut off, and the level indicator will flash.)

Figure 2 Flow with Constant-current Function

Note: Protection is not provided in case of protection short circuit. Also use a quick-burning fuse.