What’s the Difference Between Single Phase and Three Phase AC-DC Power Supplies?

Single Phase vs Three Phase AC-DC Comparison of Benefits Chart
Alternating current (AC) power is a form of electricity in which the power flow is constantly changing directions. Since the early 1900s, AC power is what has been delivered to homes and businesses. For most businesses and industrial settings, it is delivered in three phase to accommodate higher loads, whereas residences are generally provided single phase to sufficiently power household items. When designing an electronic system, it is important to consider the source of electricity and the resulting AC-DC power supply required.

General Overview of Single Phase and Three Phase AC Systems

Both single phase and three phase power systems refer to units using alternating current (AC) electric power. With AC power, the flow of current is constantly alternating directions. The primary difference between single phase and three phase AC power is the constancy of delivery.
A single phase AC power system peaks in voltage at 90⁰ and 270⁰, with a complete cycle at 360⁰ (see chart below.) With these peaks and dips in voltage, power is not delivered at a constant rate. In a single phase system, there is one neutral wire and one power wire with current flowing between them. The cyclical changes in magnitude and direction usually change flow in current and voltage about 60 times per second, depending on the particular needs of a system.
In a 3 phase system there are three power wires, each 120⁰ out of phase with each other. Delta and wye are the two types of circuits use to maintain equal load across a three phase system, each resulting in different wire configurations. In the delta configuration, no neutral wire is used. The wye configuration uses both a neutral and a ground wire. (Note: In high voltage systems, the neutral wire is not usually present for a three phase system.) All three phases of power have entered the cycle by 120⁰. By the time a complete cycle of 360⁰ has completed, three phases of power have each peaked in voltage twice (see chart below.) With a three phase AC-DC power supply , a steady stream of power is delivered at a constant rate, making it possible to carry more load.

Benefits and Uses of a Single Phase AC-DC Power Supply

Single phase AC-DC power supply units have a broad array of applications. Units that have a limited power need up to 1000 watts* typically make the most efficient use of a single phase AC power supply. Generally, benefits of selecting a single phase system include:
  • Broad array of application uses
  • Most efficient AC power supply for up to 1000 watts
  • Fewer design costs
  • Less complex designs
(*Note: Although <1000 watts are the normal output for single phase AC-DC units, there are some cases where up to 2500 watts capacity can be reached under certain circumstances. See the Aegis Power Systems CWA003 spec sheet for an example.)
Example of a 1-Phase AC-DC Power Supply with >1000W Power

Benefits and Uses of a Three Phase AC-DC Power Supply

Typical applications for 3 phase systems include data centers, mobile towers, power grids, shipboard and aircraft, unmanned systems, and any other electronic with a load greater than 1000 watts. Three phase power supplies offer a superior carrying capacity for higher load systems. Some of the benefits include:
  • Reduction of copper consumption
  • Fewer safety risks for workers
  • Lower labor handling costs
  • Greater conductor efficiency
  • Ability to run higher power loads
Additionally, three phase systems in delta configuration with a 208 volt load requires less circuit breaker pole positions than that of a wye configuration. In these cases, a three phase system yields further savings in installation, maintenance, and cost of production materials due to the reduction of required wires. However, in most cases, the wye configuration is preferable. Wye is more flexible in that it can power devices that require 3 phase, 2 phase, or 1 phase power. For example, a data center’s warehouse of servers may only require three phase power, however, the technician monitoring the servers will likely need single phase power to operate his/her computer, tools, and lights.

Should I Use A Single Phase Or Three Phase AC-DC Power Supply?


With proper care in the design phase, a power supply engineer can make appropriate recommendations for the maximum efficiency and cost savings for your particular project. Selecting a single phase or three phase PSU all depends on the power needs of a specific application. Either way, a well designed unit will ensure a reliable and robust power conversion.