USB Power Management

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USB power supply device

power management has always been one of the main links in the design and maintenance of electronic products. In the past, if users wanted to know the power supply status, they could only use the limited working instructions on the equipment; with the development of computer technology, power supply systems (such as UPS ) began to communicate with computers through RS-232 , making it much easier for users to control the power supply; but RS-232 is not perfect, and the development of bus structure has brought IEEE1394 ( high-speed serial bus ) and USB . The power supply device finally chose the USB standard suitable for medium and low-speed peripherals. This is not just following the trend, but there is a deep demand background behind it. Designing and managing power supply devices
in accordance with USB standards, fully realizing the advantages of USB devices such as plug-and-play, low power consumption and easy use and maintenance , is one of the development trends of power supply devices.

1. USB Universal Serial Bus and HID Human Interface Device
USB ( Universal Serial Bus ) is a serial interface standard jointly developed by Intel , Compaq , Microsoft , IBM , DEC , Northern Telecom and Japan's NEC . The first draft was developed in November 1994, and the USB specification version 1.0 was announced in February 1996. 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 allows you to plug or unplug devices from your system at any time, and eventually you will no longer need to set up multiple parallel and serial ports on the back of your PC . USB divides devices into different types, and each device type defines the common behavior and protocols of similar functional devices. HID ( Human Interface Device ) Human Interface Device mainly refers to devices used for people to control the operation of computer systems, while power devices ( Power Device ) are positioned as one of the subsystems of HID . The purpose of classifying devices is to eliminate the differences between different hardware manufacturers so that the host (PC) can manage the devices conveniently and uniformly. Devices of the same type are composed of a set of standard-defined functional modules. In this way, the communication between the host and the USB device can be completed through some standard format data packets. 2. HID power supply device The power management of the device is usually completed by using hardware integrated control components internally to manage the battery or internal power supply device. Similarly, for external power supply devices (such as devices powered by UPS ), there are also special control components to complete various control functions. In either case, the communication of status and control information between the host and the control component can be completed through the USB protocol, so that the host can achieve absolute control over the power supply of the device. From the perspective of the host, since 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 for the implementation of the power supply device. With the help of the HID class driver, the device driver can directly access the device on a much more friendly platform without having to consider too much about the interaction between the class driver and the low-level software of the system. In short, USB allows users to directly touch the power management of the device through the host through a series of standard definitions, greatly enhancing and facilitating the power management function. 3. Object Definition of Power Supply Devices Each power supply device consists of a set of modules (such as battery system, power converter), and each module can be subdivided into one or more submodules. Submodules can exist inside a module (such as battery, charger) or as interfaces between modules. All modules, submodules, and interfaces are defined as objects with clear physical descriptions: l Battery l Charger l Input and Output l Battery System (battery system - a collection of batteries, chargers, and input / output) l Power Supply or Power Converter (power supply or power converter - conversion and output of specific voltage and frequency)












l Outlet and Outlet System (power outlet and power outlet system - power output that can be remotely switched on and off by a PC )
l Gang (group - a collection of objects with the same characteristics and functions)
l Flow (flow - a summary description of the electrical characteristics of the power line)
l Power Summary (power report), for the power supply device to provide its own work and status messages to the host or other devices, complete the power supply's own information collection and external communication.
The composition structure of modules, sub-modules and interfaces inside different power devices is called the object hierarchy table of the power supply device, as follows:
1. Battery system:
l Input (connected to the input flow)
l Charger
l Battery (connected to the charger or output)
l Output (connected to the output flow)
2. Power converter:
l Input (connected to the output flow or output)
l Output (connected to the input flow or input)
3. Power outlet system:
l Independent power outlet (connected to the output flow)
l An input flow
l Output flow
l Power report ( connected to the output flow )
The sub-modules inside the module are directly connected, while different modules are connected through flows. The connection points are the input and output of the module.
4. Implementation of two simple power devices
1. Power supply of a typical USB peripheral

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

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


input and one AC output) l One AC output stream ( AC stream) l One power report V. Conclusion Power management and USB are two rapidly developing technical topics. Since manufacturers have added the control chip required for USB to the ASIC (application-specific IC ) of peripheral devices, PC support for USB only requires adding a socket that costs less than $ 1 . This has greatly stimulated the development of USB . Microsoft 's PC98 and PC99 systems have announced that USB and HID will be one of the industrial standards they support. As a universal device, power supply equipment is also increasingly moving towards standard unification. The implementation of USB standards in power supply equipment has greatly improved the versatility of power supply equipment and simplified the control and management of power supply equipment. It is conceivable that with the development of USB , the power devices supported by USB will also become standard power devices, all of which will make power management more standardized and easier.