动态图解晶体管开关电路及结型场效应管原理

场效应管和晶体管(三极管)皆为最常用的元件,弄清楚其原理和功能十分有必要。晶体管的功能之一即为开关,利用其截止特性,实现开关功能。文中动态图片生动的阐述了三极管作为开关的功能以及结型场效应管工作原理,值得闲暇之余淡然回味。 继续阅读“动态图解晶体管开关电路及结型场效应管原理”

Relational Databases ~ Introduction to the Relational Model

A data model is a collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints. In this part, we focus on the relational model.

The relational model uses a collection of tables to represent both data and the relationships among the data. Its conceptual simplicity has led to its widespread adoption; today a vast majority of database products are based on the relational model. The relational model describes data at the logical and view levels, abstracting away low-level details of data storage. 继续阅读“Relational Databases ~ Introduction to the Relational Model”

反激式开关电源设计解析~(上)

在开关电源市场中,400W 以下的电源大约占据整个市场的70~80%,而其中反激式电源又占绝大部分,几乎常见的消费类产品全是反激式电源。优点:成本低,外围元件少,能耗低,适用于宽电压范围输入,可多组输出。缺点:输出纹波比较大。(输出配合低内阻滤波电容或配合LC噪声滤波器可改善)本文以自行车充电器为例,详细阐述反激开关电源的设计流程及如何进行元器件的选型。 继续阅读“反激式开关电源设计解析~(上)”

Database System Concepts ~ Introduction III

The architecture of a database system is greatly influenced by the underlying computer system on which the database system runs. Database systems can be centralized, or client-server, where one server machine executes work on behalf of multiple client machines. Database systems can also be designed to exploit parallel computer architectures. Distributed databases span multiple geographically separated machines. 继续阅读“Database System Concepts ~ Introduction III”