USB port power management

USB port power management

Power management has always been one of the main links in the design and maintenance of electronic products. In the past, users who wanted to understand the power supply could only use the limited work instructions on the equipment; with the development of computer technology, power supply systems (such as UPS) began to communicate with computers via RS-232, enabling users to control power supply greatly Convenient; but RS-232 is not perfect, the development of the bus structure has brought IEEE1394 (high-speed serial bus) and USB. The power supply device finally chose the USB standard suitable for low- and medium-speed peripherals. This is not in fashion, there is a deep background of demand behind it.

It is one of the development trends of power supply equipment to follow the USB standard to design and manage power supply equipment, fully realize the plug-and-play use of USB equipment, low power consumption and easy maintenance.

One. USB Universal Serial Bus and HID Human Machine Interface Equipment

USB (Universal Serial Bus) is based on Intel, and has a serial interface standard jointly developed by seven companies including Compaq, Microsoft, IBM, DEC, Northern Telecom and Japan NEC. The first draft was formulated in November 1994 In February 1996, the USB specification version 1.0 was announced. USB can connect up to 127 peripherals to your system, and its 12Mbps bandwidth is completely sufficient for low and medium speed peripherals such as keyboards and mice. This technology enables you to plug in or unplug your system at any time, and you will eventually no longer need to have multiple parallel and serial ports behind your PC.

USB divides devices into different types, and each device type defines the common behavior and protocol of similar functional devices. HID (Human Interface Device) human-machine interface device mainly refers to a device used for human to control the operation of a computer system, and a power device (Power Device) is positioned as one of the subsystems of HID. The classification of devices is to erase the differences between different hardware manufacturers, so that the host (PC) can manage the devices conveniently and uniformly. The same type of equipment is composed of a set of standard-defined function modules. In this way, the communication between the host and the USB device can be completed through some standard format data packets.

two. HID power supply

The power management of the equipment is usually through the internal integration of hardware control components to complete the management of the battery or the internal power supply device. Similarly, for external power supply equipment (such as equipment powered by UPS), there are special control components to complete various control functions. In any case, the status and control information between the host and the control unit can be completed through the USB protocol, so that the host can achieve absolute control of the power supply of the device.
From the perspective of the host, because the USB power supply device protocol is designed in the framework of the USB human-machine interface device, the HID class driver on the host is the foundation of the power supply device implementation. With the help of the HID class driver, the device driver can directly access the device on a much more friendly platform, without much consideration of the interaction between the class driver and the low-level software of the system.

In short, USB is defined by a series of standards, so that users can directly touch the power management of the device through the host, which greatly enhances and facilitates the power management function.

three. Object definition of power supply

Each power supply is composed of a group of modules (such as battery system, power converter), and each module can be subdivided into one or more sub-modules. Submodules can exist inside the module (such as batteries, chargers), or they can be interfaces between modules. All modules, submodules, and interfaces are defined as objects, with a clear physical description:

Battery
Charger
Input and Output
Battery System (battery system-a collection of batteries, chargers and input / output)
Power Supply or Power Converter (power supply or power converter-specific voltage, frequency conversion, output)
Outlet and Outlet System (power outlet and power outlet system-power output that can be remotely controlled by a PC)
Gang (group--a collection of objects with the same characteristics and functions)
Flow (summary description of the electrical characteristics of the power cord)
Power Summary (power report), for the power supply equipment to provide its own work, status information to the host or other equipment, complete the power supply information collection and external communication,

The structure of modules, small modules and interfaces inside different power devices is called the object hierarchy table of power devices, as follows:

1. Battery system:
Input (connect to input stream)
Charger Battery (connect to charger or output)
Output (connect to output stream)

2. Power converter:
Input (connect to output stream or output)
Output (connect to input stream or input)

3. Power outlet system:
Independent power outlet (connected to output stream)
One input stream output stream power report (connected to output stream)

The sub-modules inside the module are directly connected, while the different modules are connected by flow, and the connection points are the input and output of the module.

four. Realization of two simple power devices

1. Power supply for a typical USB peripheral

figure 1. Power supply for typical USB peripherals

One AC input stream, one DC input stream (USB bus power)
A power converter (including an AC input, a DC input and a DC output)
One DC output stream and one power report

2. A simple UPS power supply An AC input stream (main AC input)
One battery system (one AC input, one battery, one charger and one DC output)
One DC stream (backup DC)
One power converter (one DC input, one AC input and one AC output)
One AC output stream (AC stream)
A power report

figure 2. Simple UPS power supply


V. Conclusion

Power management and USB are two rapidly developing technology topics. Since manufacturers add the control chip required by USB to the ASIC (dedicated IC) of peripheral devices, PC support for USB only needs to add a socket with a cost of less than $ 1. This greatly stimulated the development of USB. Microsoft's PC98 and PC99 systems have announced USB and HID as one of the supported industry standards. As a general-purpose device, the power supply device is also developing towards the standardization. The realization of the USB standard in the power supply device greatly improves the versatility of the power supply device and simplifies the control and management of the power supply device. It is conceivable that with the development of USB, power devices supported by USB will also become standard power devices, all of which will make power management more standard and easier.

6. Some references and sites Universal Serial Bus SpecificaTIon, Revision 1.0, January 15, 1996
Universal Serial Bus Device Class DefiniTIon for Human Interface Devices (HID),

Version 1.0 Final
Universal Serial Bus HID Usage Tables, Release Candidate 1.0
Universal Serial Bus Usage Tables for HID Power Device, Release 1.0






Attachment: Meaning of the phrase in the illustration:
AC FLOW: alternating current
USB BUS POWER: USB bus power
INPUT: input
OUTPUT: output
DC FLOW: DC
POWER SUMMARY: Power report

MAIN AC: Main power supply AC
CHARGER: Charger
BATTERY: battery
BACKUP DC: Backup DC power
BATTERY SYSTEM: battery system
POWER CONVERTER: power converter

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