欢迎访问ic37.com |
会员登录 免费注册
发布采购

VT400 参数 Datasheet PDF下载

VT400图片预览
型号: VT400
PDF下载: 下载PDF文件 查看货源
内容描述: 感光细胞和模拟光隔离器( Vactrols ) [Photoconductive Cells and Analog Optoisolators (Vactrols)]
分类和应用:
文件页数/大小: 76 页 / 1202 K
品牌: PERKINELMER [ PERKINELMER OPTOELECTRONICS ]
 浏览型号VT400的Datasheet PDF文件第39页浏览型号VT400的Datasheet PDF文件第40页浏览型号VT400的Datasheet PDF文件第41页浏览型号VT400的Datasheet PDF文件第42页浏览型号VT400的Datasheet PDF文件第44页浏览型号VT400的Datasheet PDF文件第45页浏览型号VT400的Datasheet PDF文件第46页浏览型号VT400的Datasheet PDF文件第47页  
Characteristics of Analog Optical Isolators  
Storage at low temperature has no operating effect on AOIs. Units may  
Storage Characteristics  
be stored at temperatures as low as -40°C. Lower temperatures may  
cause mechanical stress damage in the package which can cause  
permanent changes in the AOI transfer characteristics.  
The instantaneous output resistance of any AOI is somewhat  
dependent on the short term light history of the photocell output  
element. With no applied input current or voltage, the output element is  
in the dark. Dark storage causes the cell to dark adapt, a condition  
which results in an increase in the photocells sensitivity to light. When  
first turned on, an AOI which has experienced a period of dark  
adaption will exhibit a lower value for on” resistance, at any given drive  
condition, than the same device which has been continuously on.  
The chemistry of the photoconductive materials dictates a maximum  
operating and storage temperature of 75°C. It should be noted that  
operation of the photocell above 75°C does not usually lead to  
catastrophic failure but the photoconductive surface may be damaged,  
leading to irreversible changes in sensitivity.  
The amount of resistance change is a function of time as well as  
temperature. While changes of several hundred percent will occur in a  
matter of a few minutes at 150°C, it will take years at 50°C to produce  
that much change.  
The output resistance of an AOI which has been biased on” is  
considered to be constant with time (neglecting long term aging  
effects). After the removal of the input drive, the photocell begins to  
experience dark adaption. The cells rate of increase in sensitivity is  
initially high but eventually levels off with time in an exponential  
manner. Most of the dark adapt occurs in the first eight hours, but with  
some AOIs for sensitivity can continue to increase for several weeks.  
When an AOI which has been sitting in the dark is turned on, the cell  
immediately begins returning to its light adapted state. For any given  
device, the rate of recovery is dependent on the input light level.  
In most applications, operation is intermittent. At elevated  
temperatures, the resistance of the cell rises during the turn-on period  
and recovers during the turn-off period, usually resulting in little net  
change. However, if the AOI is stored at elevated temperatures for  
many hours with no input signal, there is a net reduction in output  
resistance. There will be some recovery during operation over time but  
it is not possible to predict the rate or to what degree. Elevated  
temperatures do not produce sudden catastrophic failure, but changes  
in the device transfer curve with time must be anticipated.  
The type of photoconductive material is the major factor determining  
the magnitude of these changes. Lower resistivity materials show  
greater initial and final changes but their rate of change is faster.  
These light/dark history effects are pronounced at both high and low  
input levels. However, at high input levels, the photocell light adapts  
quite rapidly, usually in minutes.  
Figure 1 shows the transfer curves for an AOI after 24 hour storage  
with no input and then after it has been operated with rated input for 24  
hours. Because of these memory” phenomena, it is best to use these  
parts in a closed loop circuit to minimize the effects of these changes.  
Open loop proportional operation is possible if the application can  
tolerate variations. The use of the VTL5C2 and VTL5C3 with their  
more stable characteristics will help.  
Temperature Range  
Operating and storage temperature range is limited at the lower end by  
the reduction of dark resistance of the cell and at the upper end by  
rapid aging. At low temperatures, the response time of the output cell  
increases. The temperature at which this becomes pronounced  
depends on the photoconductive material type. Isolators using low  
resistivity materials, as in the VTL5C4, will show this lengthening of  
response time at -25°C. Higher resistivity materials such as used in the  
VTL5C3 and VTL5C6 do not slow down excessively until temperatures  
get below -40°C. This characteristic is completely reversible with the  
response time recovering when the temperature rises.  
38