Powered by USB to a green future by VR-Zone.com

Our first guest writer is René F. Koch, the CTO of Leader Electronics Inc. which is one of the largest OEM/ODM designers and manufacturers of power adapters and various types of power supplies. Leader Electronics Inc. has over 40 years of experience in the industry making product ranging from phone chargers, to notebook chargers all the way to various industrial solutions. René has been working for Leader Electronics Inc. for over a decade in various positions at the company and his guest feature is about where things seem to be heading as far as device charging is concerned and why we’re heading in that direction.



The Universal Serial Bus, or simply USB, has from its launch always been able to provide power to the connected device and it’s now transforming into the new Universal Power delivery system, according to a recent publication from the USB implementers forum. The strength of USB has always been its ability to provide power, next to a means of being an interface, as this allowed for a single cable connection to be used with a wide variety of devices like Human Interface Devices (mice, keyboards, etc.), microphones, speakers, storage devices and so on.

Until recently, the current limit was 500mA for configured high-power devices and 100mA for un-configured or low-power devices; with a standardized bus voltage of 5V this results in a maximum power of 2.5W, similar to the power needed for a normal mobile phone charger. The European Union was interested in making this the mandatory mobile phone charger standard, as that could result in major "Green" benefits. Most people have had multiple mobile phones over the past decade; as functionality increased, people would buy new models, leaving their old phone with a still functional charger as waste, while buying multiple chargers, for home, work and in the car for example. Waste is a growing concern, especially in electronic goods; the EU therefore, figured this a good opportunity to reduce the amount of waste, as the chargers do not offer any additional functionality with newly released phone models.

Although most major mobile phone brands agreed to the proposed standard and signed the MOU that was initiated by the EU, most of them are not yet willing to ship their products without a charger; this is especially true for higher-value products. The rationale is that a lower quality charger, which does not completely comply with the requirements, could render mobile phones useless or even worse, making the battery explode as seen in the past. Nevertheless, the future trend is set for a universal charger and is destined to become reality. Other types of products take advantage from this initiative, especially those that are battery operated and are charged by USB; look at Digital Cameras, tablets and smartphones. Even products that do not even need to communicate over USB, like wireless DECT phones or LED flash lights use USB ports to connect to their charger.

If you wanted to use more power from a USB port than 2.5W you could choose to use two USB plugs, as often is the case with external 2.5-inch hard drives, alternatively, an external power supply could provide the additional power. Now, with the introduction of USB 3.0, the current capability was raised up to 900mA for super-speed ports, almost doubling the power delivery capability. Meanwhile, an additional feature was added to the USB standard in order to provide more power to connected devices, in particular to be able to charge battery operated handheld devices. The new standard is known as the “Battery Charger Standard” and in late December last year, V1.2 was released, which allows currents beyond 1.5A, up to a maximum of 5A, resulting in a power delivery capability up to 25W. The key feature of this charging standard is a dedicated USB mode which is initiated by a resistive pull-up / -down configuration of the data pins. With a maximum current handling capability of 1.8A for the connector-pins in a micro USB plug, the cables and connectors of the USB standard are now the limiting factor to deliver more current and, as the voltage is standardized to 5V, also to power.

This is where the new power delivery standard will come in, as the Voltage will be negotiable in the future, by digital communication between the host and connected device, and could go as high as 60V DC; limited for safety reasons to the maximum Voltage of a Safe Electrical Low Voltage (SELV); a Voltage that does not result in a shock hazard when touched. In theory this could mean up to 100W, with the 1.8A of current handling capability as maximum limit (1.8A * 60V = 108W). Handling higher currents, like the absolute limit of 5A, as defined in all USB specifications, even if connectors and cables could handle this current, is however not a good solution for energy efficient transport of power.

Current creates losses in cables and connections; the lower the current, the lower the power loss. (Ploss = I2 * R). As such 100W would be the maximum power that could be delivered over a single USB port, which means that when using a 4-port USB hub, up to 400W could be delivered. This power level goes way beyond the practical needs of most computing equipment; dedicated gaming or CAD computers, or their imaging peripherals might need more power, but then again, this power delivery system is not meant to power computer systems but rather peripherals, with a possible extension to charge notebook computers or other handheld battery operated devices. Thinking about the opportunities and possibilities this power delivery standard could offer, it could very well change the world of power electronics, and power delivery as we know it.

Energy Performance standards, which are mandatory in most western parts of the world, focus on active mode energy efficiency and off-mode, stand-by and no-load power consumption.

Active mode energy efficiency is quite clearly the capability of the system to perform a certain action while limiting the energy required doing so. Although actions are not always easily translated into power, the EU tries to generalize actions and reflect a certain calculation on them in order to establish the system performance of that action in relation to the used power consumption to perform said action. (The U.S.D.O.E. is starting similar activities)

There are three modes of operation while the system is not actually performing its primary task:

· Off-mode, in which the device / system is still powered, but not performing any action;

· Standby-mode, in which the system is idle, waiting for an instruction to perform its primary action, and

· No-Load, in which the power supply is connected, but the device is not connected to the power supply.

Basically, any energy draw during these three modes of operation is waste, as there is no action being performed.

An additional state of non-active mode is now added to the scope, which is referred to as “networked stand?by”. This mode comes into scope when thinking about all the USB powered devices that do not have their own power supply. At this time, each connected device needs to draw less than 500mW of power while in a non-active mode according to mandatory energy efficiency regulations. The USB standard actually defines a “suspend” mode in which no more than 2.5mA (12.5mW) can be drawn from the bus, but does not mandate a suspend mode.

Connecting 4 devices to one USB hub, would result in a stand-by consumption of 2A (4 * 500mA), while the USB hub itself should also draw less than 500mA. As the system can be considered to be idle during night time, the total power consumption of this configuration could add up to 2.5A * 5V = 12.5W. This is a lot of wasted energy, but still in-line with the current regulations. In order to reduce this waste, there is an obvious need for smarter power distribution. Using USB can provide all the hardware needed to grow into an eco-system that incorporates smart power distribution, without the need for new standards, connectors or interfaces.