USB PD vs. USB-C: Differences, Benefits, and Adapters

USB Power Delivery (PD) is a specification that allows the output voltage of a power supply to be programmed by the load. It has proven to be a revolutionary change when combined with the USB Type-C connector, allowing devices to transmit both power and data while the adapter adjusts to the power requirements of the device using it.

This article discusses the distinctions and overlaps between USB PD and USB-C more generally before investigating the benefits of USB power delivery in design ecosystems with competing, distinct power requirements.

It also provides a brief discussion of the design considerations for USB PD adapters before concluding with an example of a recent power delivery solution developed by CUI.

 

Figure 1. USB PD allows users to charge and power multiple devices, such as tablets and smartphones, with each device only drawing the power it needs. Image used courtesy of Pixabay.

 

How USB-C and USB PD Differ

First, USB PD and USB-C are different standards. The USB-C standard describes the physical connector. The use of the connector does not necessarily mean an adapter has USB PD functionality. An engineer can choose USB type-C connectors for a design without opting to conform to USB PD. USB type-C connectors, however, do provide the ability to transfer both moderate power (up to 240 W) and data over the same cable in addition to having a symmetrical, self-aligning connector that makes it far easier to insert successfully. 

Here’s a summary of USB charging as it stands:

• Legacy USB 2.0 at least 5 V and up to 500 mA (think legacy USB 2.0)
• USB 3.1 supports 5 V and 900 mA
• USB-C supports two different power profiles: 5 V and 1.5 A or 5 V and 3 A

Previous USB power standards are limited in that they cannot provide multiple power levels for different devices. The USB PD specification, however, allows the power supply and device to negotiate for an optimum power delivery method.

Each device will start with an initial low power level at 5 V up to 10 W. From there, power negotiation takes place, and depending on the device's needs, the transferred power can be up to 240 W. 

The USB PD negotiation approach has voltage steps of 5 V, 9 V, 15 V, 20 V, and beyond that support power outputs ranging from as little as 0.5 W to 240 W by varying current.

USB PD can support higher output power levels by allowing devices to negotiate for power levels. It makes USB power adapters capable of powering more than one specific device at more optimum levels and makes it possible to achieve faster charge times—all of which enhance the capabilities of the USB technology. 

 

Pros and Cons of USB Power Delivery?

One of the immediate benefits of USB PD is that more than one mobile device can be charged at optimal levels by the same adapter, even if the devices have different charging voltage requirements, all made possible when combining USB-C with the USB PD power negotiation protocol. However, this is only one of the benefits, especially when combined with USB type-C connectors and cables. 

For example, combining USB type-C and USB PD reduces the number of chargers and cables needed to power multiple devices, making life much simpler for end users and supporting the ability of manufacturers to use one charger and cable for more of their devices.

Another benefit of USB PD is 28 V, 36 V, and 48 V negotiated voltages that enable up to 140 W, 180 W, and 240 W power levels, respectively, through the availability of several different constant voltage levels with variable currents. 

Further, the USB PD standard includes an adjustable voltage supply mode that engineers can configure. It allows the device to request intermediate voltages that lie between 5 V up to the maximum available fixed voltage of the charger, as opposed to the voltage steps just described. 

Further, the power direction is no longer fixed: either the host or the peripheral device can provide power based on the current power needs of the devices connected to the charger. 

 

Figure 2. Voltages and current limits defined by USB PD vs. source power rating. Image used courtesy of CUI. (Click on image to enlarge)

 

In addition, power management can be optimized across multiple peripherals, allowing each device to receive the power it needs and more power when needed—and lower power devices, such as headsets, can receive only the power they require through power negotiation and handshaking. USB PD also supports interoperability between conforming implementations of older and newer versions of USB specifications.

There are, however, drawbacks to USB PD. Among these are the fact that lines previously reserved for data transfer may be used for power instead. There may also be a lack of 3rd party accessories until USB type-C combined with USB PD are more widely used together.

 

Finding the Right USB PD Adapter

Keep in mind that both USB type-C and USB PD are standards, which means it is critical to ensure the power adapter under consideration complies with both of these standards. There are, of course, several other things to look for in an external power adapter, including the following:

• System power requirements
• Package type
• DC plug and cable options
• Efficiency regulations
• Safety standards
• Branding and system integration

 

CUI USB Power Delivery Solutions

CUI recently expanded its family of AC-DC USB type-C adapter power supplies with USB PD 3.0 capabilities. The two new series are the SWI60C-E Series (European model shown in Figure 2) and the SWI60C-N Series (North American model). They comply with the USB PD 3.0 standard and meet Level VI DOE efficiency standards for Canada and the United States and  Ecodesign 2019/1782  standards for Europe. They are also UL 62368 / EN 62368 safety certified.

 

Figure 3. The CUI SWI60C- E series shown, as well as the N series, comply with the USB PD technical standard. Image used courtesy of CUI.

 

These wall plug models support up to 60 W continuous power and have 5 to 20 VDC output options with a no-load power consumption of less than 0.21 W. They also include protections for over current, over voltage, and short circuits. Both CUI SWI60C-N and SWI60C-E power adapters have a small form factor of only 65 mm × 65 mm × 28 mm for a minimum footprint. As with all CUI power adapters, a wide range of customization options exist, including branding and cable length.

 

AC-DC Power Adapter Solutions

CUI offers a wide range of compact, highly efficient external AC-DC power adapters. USB PD adapters, such as the CUI SWI60C E and N series, can be used with devices, including smartphones, digital cameras, tablets, notebooks, and monitors.

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