![]() |
Electronic Components Datasheet Search |
|
VTL5C1 Datasheet(PDF) 43 Page - PerkinElmer Optoelectronics |
|
|
VTL5C1 Datasheet(HTML) 43 Page - PerkinElmer Optoelectronics |
43 / 76 page ![]() 38 Characteristics of Analog Optical Isolators Storage 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 photocell’s 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 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 cell’s 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. 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. Storage at low temperature has no operating effect on AOIs. Units may 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 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. 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. |
Similar Part No. - VTL5C1 |
|
Similar Description - VTL5C1 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |