Everything You Need to Know About Power Supplies

AC Connection

The first thing you should know is that your power supply must be compatible with the AC voltage used in your city. The most common ones are “110 V,” covering voltages that approximate this value (for example, 115 V and 127 V), and “220 V”(for example, 230 V and 240 V).

Most power supplies will have either a 110 V/220 V switch or will be “auto range” or “auto select,” meaning that they can work under “any” AC voltage (usually between 100 V and 240 V; the range is printed on the power supply label, under “AC Input,” see Figure 3) Therefore, they don’t come with this kind of switch. Usually manufacturers make the “auto select” circuit through the active PFC circuitry, so all power supplies with active PFC will be “auto range” and won’t have a 110 V/220 V switch. Only a very few power supplies with automatic voltage selection won’t have an active PFC feature. Of course we will explain what this circuit is later.

Not all power supplies that don’t have a 110 V/220 V switch are auto range. Some power supplies can only operate under a specific voltage. These are most commonly targeted to the European market. If you see a power supply without a 110 V/ 220 V, it is always a good idea to double check the power supply label under which the AC voltage can work.

Figure 1: Power supply 110 V/220 V switch.

Figure 2: Power supply with auto voltage select – no 110 V / 220 V switch. Usually this means that the unit has active PFC.

Figure 3: The voltage range for power supplies with auto voltage select is described on the power supply label.

The connection between your power supply and the AC outlet is done through a power cord. This power cord must use a plug compatible with the standard used in your country. If your plug doesn’t conform to that standard, you will need to use an adapter. The two most common plug types are the North-American (NEMA 5-15) and the European (CEE 7/7). Other countries may use different plug types (for example, the UK use a plug called BS 1363).

Figure 4: North-American power cord.

Figure 5: European power cord.

The end of the power cord that is connected to the power supply uses a trapezoid-shaped plug called an IEC C13, while the receptacle for the power cord located on the power supply uses a plug called an IEC C14. Other plugs can also be used on this connection, such as an IEC C19 and an IEC C20, but they are not as common.