Q&A(FAQ) Is it possible to apply DC voltage to an AC-DC power supply?
1. Operation with a DC Input Voltage
In switch-mode power supplies, the AC input voltage is first rectified and converted to DC, so these units can generally operate from a DC input. However, models with an input-voltage selector should not be operated with DC input.
Because the rectified voltage is smoothed by a capacitor, the applied DC voltage must match the peak value of the AC input. Therefore, when using a DC input, a voltage equal to the rated AC voltage multiplied by √2 must be applied. Please refer to the DC input voltage specifications in the COSEL catalog.
2. Wiring for DC Input
2.1 Overview
Because a full-wave rectifier is built into the power supply, either polarity (positive or negative) can be connected to either input terminal.
2.2 Recommended Wiring
Although the positive voltage may be applied to either input terminal, COSEL recommends applying the positive voltage to the AC(L) terminal, which is equipped with a fuse (see Fig. 2.1).
When applying a DC input to an AC-DC power supply, install a DC-rated fuse on the input line to provide protection in the event of a power supply failure.
2.3 Internal Fuse
Most power supplies are equipped with an AC-rated fuse. When operating the unit with a DC input, a DC-rated fuse must be added to the input line, as an AC-rated fuse may not operate safely under abnormal DC conditions.
2.4 Conditions of Acceptability for Safety Approval
Most universal-input AC–DC power supplies are certified for input voltage conditions of 100 VAC to 240 VAC (50/60 Hz). Therefore, safety approvals do not apply to DC input operation, except for products that are explicitly certified for DC input. Please refer to the instruction manual for each product for detailed specifications.