Can I use DC input to run AC-DC power supply?
The answer is yes, at certain times and conditions.
Many standard AC-DC switching power supplies (most of Lambda's products) specify a higher DC input range outside the 90-264VAC, the most common AC input range. We will receive a lot of questions about how to connect the DC input to the AC-DC power supply that AC-DC input can be applied to, how to connect, where to connect, etc.
Where are the high-voltage DC power supplies used and why? It turns out that many power stations provide high voltage DC instead of the usual 115VAC or 208VAC power grids to power the plant's equipment. This high-voltage direct current (typically 120 or 130-330VDC) can be easily combined with the battery to ensure power supply without the need for expensive centralized systems or local uninterruptible power supply systems.
Now back to the topic. Many switching power supply topologies can actually operate under AC or DC input conditions. Important: Please refer to the power supply's application manual or specifications to confirm that the power supply design is suitable for operation under AC or DC input.
Please refer to the schematic diagram of the power supply as follows:
When powered by an AC sine wave, current flows through the input filter through the input during the first half of the cycle, and capacitor C1 is charged through diodes D1 and D3. In the second half cycle (negative input), current flows in through the neutral line and charges capacitor C1 through diodes D2 and D4.
When powered by high voltage direct current, the polarity of the connection is not critical for power operation. If a positive input is connected at the hot terminal, C1 is charged via diodes D1 and D3. If a positive input is connected at the neutral terminal, C1 is charged through diodes D2 and D4.
An important consideration here is related to the protective fuse of the power supply. Most power supplies have an AC fast fuse in series with the input. It is recommended to install the DC fuse outside the power supply. If one end of the HVDC bus is grounded, the fuse is normally placed in series with the high-potential side (not grounded). It is advisable to consult a local safety engineer for confirmation.
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