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| 两侧同时换到之前的修订记录 前一修订版 后一修订版 | 前一修订版 | ||
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ldo [2016/06/02 19:35] gongyu [稳压] |
ldo [2016/06/02 19:51] (当前版本) gongyu [输出噪声] |
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| ====指标==== | ====指标==== | ||
| - | An LDO is characterized by its drop-out voltage, quiescent current, load regulation, line regulation, maximum current (which is decided by the size of the pass transistor), speed (how fast it can respond as the load varies), voltage variations in the output because of sudden transients in the load current, output capacitor and its equivalent series resistance.[10] Speed is indicated by the rise time of the current at the output as it varies from 0 mA load current (no load) to the maximum load current. This is basically decided by the bandwidth of the error amplifier. It is also expected from an LDO to provide a quiet and stable output in all circumstances (example of possible perturbation could be: sudden change of the input voltage or output current). Stability analysis put in place some performance metrics to get such a behaviour and involve placing poles and zeros appropriately. Most of the time, there is a dominant pole that arise at low frequencies while other poles and zeros are pushed at high frequencies. | + | 评价一个LDO主要的指标有： |
| + | * 电压差 | ||
| + | * 静态电流 | ||
| + | * 负载调整率 | ||
| + | * 线调整率 | ||
| + | * 最大电流（取决于导通晶体管的大小） | ||
| + | * 对负载变化的响应速度 | ||
| + | * 由于负载电流的突变、输出电容以及等效的串行阻抗对输出电压的影响 | ||
| ====电源抑制比==== | ====电源抑制比==== | ||
| 行 75: | 行 82: | ||
| ====输出噪声==== | ====输出噪声==== | ||
| - | The noise from the LDO itself must also be considered in filter design. Like other electronic devices, LDOs are affected by thermal noise, bipolar shot noise, and flicker noise.[9] Each of these phenomena contribute noise to the output voltage, mostly concentrated over the lower end of the frequency spectrum. In order to properly filter AC frequencies, an LDO must both reject ripple at the input while introducing minimal noise at the output. Efforts to attenuate ripple from the input voltage could be in vain if a noisy LDO just adds that noise back again at the output. Texas Instruments' TPS7A47 is an example of an LDO with both very low noise and high PSRR over a broad frequency band.[13] | + | LDO自身产生的噪声也应该被考虑在滤波器的设计中，与其它电子器件一样，LDO也受到热噪声、双极散射噪声、以及闪变噪声的影响。所有这些噪声叠加在一起影响了输出的电压，这些噪声主要分布在低频段。为了滤除交流频率，在输入端和输出断都要进行纹波抑制。 |
| ====负载稳压==== | ====负载稳压==== | ||
| Load regulation is a measure of the circuit’s ability to maintain the specified output voltage under varying load conditions. Load regulation is defined as: | Load regulation is a measure of the circuit’s ability to maintain the specified output voltage under varying load conditions. Load regulation is defined as: | ||