[经验]

电阻放电能量对缓冲二极管串联电阻的影响

2018-10-17 15:05:08

1799 安森美二极管电阻

半导体封装，无论是用于复杂的IC还是更简单的分立器件，都在不断变小。
此外，新的封装结构设计可提供更好的封装热传递。
这些技术进步为设计人员提供了更多可用封装，性能和成本选择。
由于竞争将这些效率推向更小的几何形状和更低的成本，因此从电感器到其缓冲二极管的能量转移变得越来越重要。
通过充分了解电路串联电阻和二极管之间的功耗之间的关系，可以优化系统成本和性能。
通过连接在电感器上的缓冲二极管放电的功率受到电路串联电阻的影响。
电感器内产生的能量必须耗散，因此电流流过缓冲二极管的时间长度和串联电阻直接与串联电阻值有关。
由此可以清楚地看出，串联电阻的值将对应该指定的二极管产生重大影响。
随着串联电阻的降低，二极管中消耗的能量将增加。
因此，降低电感器的效率导致电感器具有更高的电阻和更低的成本。
这种低成本的电感器将使二极管运行更冷，并且将允许更低成本的二极管。
设计工程师需要做出妥协 - 权衡成本和系统性能，以实现更平衡的组件选择。
根据具体应用，他们可能选择更高的串联电阻，更低成本的电感器来帮助消除二极管中可能消耗的一些功率，或相反地选择更低的串联电阻，更高成本的电感器以便共享一些
电感器用缓冲二极管加热。
除了这一重要动态之外，还必须考虑占空比对长期供暖的影响。
在每个白皮书详细列出的例子中，电路中的所有电阻都用单个串联电阻“R”表示。
如上所述，“R”具有不同的充电和放电值。
功耗的两个特别重要的因素是单脉冲和周期性负载循环值。
在设计过程中必须认真考虑这两个参数。
详细说明了许多公式，可以绘制电感的充电和放电曲线。

以上来自于谷歌翻译

以下为原文

Semiconductor packaging, whether it is for complex ICs or more simple discretes, is getting smaller all the time.  Additionally, new package construction designs provide better heat transfer out of the package.  These technology advancements offer an increased selection of available package, performance and cost choices to the designer.  As competition drives these efficiencies to even smaller geometries and lower costs, the transfer of energy from an inductor to its snubber diode has become increasingly important. By fully understanding the relationship between the power dissipated in the circuit’s series resistance and diode, it is possible to optimize system cost and performance.
The power being discharged through a snubber diode connected across an inductor is impinged upon by the circuit’s series resistance. Energy generated within the inductor must be dissipated and therefore the length of time current flows through the snubber diode and the series resistance relates directly to the value of the series resistance.  From this it is clear that the value of the series resistance will have a major influence on the diode that should be specified.
The energy that is dissipated in the diode will increase as the series resistance is lowered. Therefore, reducing the efficiency of the inductor, results in an inductor with higher resistance and lower cost.  This lower cost inductor will result in a diode running cooler and will allow a lower cost diode.  There are compromises that design engineers will need to make - trading off cost and system performance to achieve a more balanced component selection.  Depending on the application, they may either chose a higher series resistance, lower cost inductor to help dissipate some of the power that would have been dissipated in the diode, or conversely a lower series resistance, higher cost inductor in order to share some of the inductors heat with the snubber diode. In addition to this important dynamic, the impact that duty cycle has on long term heating must also be taken into account.

In the example outlined in detail per this whitepaper, all the resistance in the circuit has been represented by a single series resistance “R”. As described, “R” takes on different values for charging and discharging.  Two contributors to power dissipation that are of particular interest are the single pulsed and the periodic duty cycled values. Both of these parameters must be given serious consideration during the design process. Numerous equations are detailed that enable the inductor’s charging and discharging profiles to be plotted.