| Bootstrapping Electronics |
Article Index for Bootstrapping |
Website Links For Electronics |
Information AboutBootstrapping Electronics |
| CATEGORIES ABOUT BOOTSTRAPPING ELECTRONICS | |
| electronics | |
| electricity distribution | |
|
The term bootstrap has a number of meanings in Electronics . ELECTRONICS In classical Analog designs, a bootstrap circuit is an arrangement of components used to boost the Input Impedance of a circuit by using a small amount of positive Feedback , usually over two stages. This was often necessary in the early days of Bipolar Transistor s, which inherently have quite a low input impedance. The need for such arrangements has largely been alleviated by the use of modern Field Effect Transistor designs, except when ultra-high input impedances are required. Note that because the feedback is positive, such circuits usually suffer from poor stability and noise performance compared to a circuit that doesn't bootstrap. AMPLIFIERS AC amplifiers can use bootstrapping to increase output swing. A capacitor is connected from the output of the amplifier to the bias circuit, providing bias voltages that exceed the power supply voltage. Emitter followers can provide rail-to-rail output in this way, which is a common technique in class AB audio amplifiers. check bootstrap capacitor. COMPUTER SYSTEMS Another meaning is in connection with the Booting process of a Computer or other complex system, where the underlying electronics must arrange for the orderly startup of the CPU and related electronics components. This is done long before the CPU is in a state where it can begin to execute software. Nowadays the bootstrap is coordinated by special Integrated Circuit s that monitor the raw Power Supply and provide the relevant signals to enable the CPU and other chips accordingly. AUTOMOBILES In a typical car Alternator , a DC field current is required before the device can produce any output. Once running, a small portion of the output is fed back to keep the field alive — this can be seen as a form of bootstrapping. The initial priming current is usually obtained from the vehicle's Battery — if the battery is totally flat the alternator won't produce any output voltage to spark the plugs or recharge the battery (by push starting for example) since it will be unable to bootstrap itself. However, in practice, a battery will usually have enough residual charge to avoid this. POWER GRIDS In reference to a regional or national which do not contain Permanent Magnets , and are incapable of starting to produce electricity unless they are fed some from an outside source to energize the coils and produce a magnetic field. Once running, they use their own output power for this purpose and are self-sustaining. Some power plants are designated within the grid as being capable of a cold start (either because they have main generators which contain magnets, or have smaller auxiliary generators which do and which are capable of bringing the main ones up), and these plants are brought on-line first, and their power output directed across the grid to other plants and used to start them. In this way, generating stations across the network can be progressively brought back up. |
|
|