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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 ]
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Characteristics of Analog Optical Isolators  
Voltage Rating  
Power Rating  
The maximum voltage rating of the output element (photocell) applies  
only when the input is off. Two different kinds of dark current leakage”  
characteristics are observed in photocell output elements. Figure 4  
shows the soft breakdown found in lower resistivity materials. With no  
Photocells are primarily used for signal control since the maximum  
allowable power dissipation is low. Typically, the steady-state output  
current should be kept below 10 mA on catalog LED AOIs because of  
the small size ceramic used in the output cell. However, the surface  
area is large compared to similarly rated transistors, so AOIs withstand  
significant transient current and power surges.  
input, if the applied voltage is suddenly increased from zero to V , the  
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current increases along section a, with the steepness depending on  
the rate at which the voltage is increased. If the voltage is now held at  
V1, the current decreases along curve b’ and stabilizes at a much  
lower value. If the voltage is again increased, the next section of the  
curve is traversed with the current dropping along curve d’ in time.  
This process can be repeated until the reverse current becomes so  
great that the cell burns up. The maximum voltage rating for photocells  
with this soft reverse characteristic is based on a safe steady-state  
power dissipation in the OFF condition.  
Power ratings are given in the catalog and are typically a few hundred  
milliwatts, but special AOIs have been made with power dissipation  
ratings as high as 2.0 W.  
Life and Aging  
Life expectancy of an AOI is influenced both by the input and output  
devices. Isolators which use an LED have long life since LED lifetimes  
are long: 10,000 to 200,000 hours, depending on the application. LEDs  
normally show a decrease in light output for a specified bias current as  
they age.  
The photocell output elements in AOIs show an increase in output  
resistance over time as they age. With a continuous input drive current  
and with voltage bias applied to the output, the output resistance will  
generally increase at a rate of 10 percent per year. The aging rate is  
lower with intermittent operation. Figure 5 shows the trend line for  
output resistance under typical operating conditions. Other AOIs using  
different photoconductive materials show similar trends.  
Figure 4. Breakdown characteristics of photocells with low resistivity  
photoconductive material.  
Higher resistivity photoconductive materials do not show the reverse  
characteristics of Figure 4 to any significant degree. As voltage is  
increased, the dark current increases, but remains very low until  
breakdown occurs. The current then increases in an avalanche fashion  
resulting in an arc-over which causes the cell to be permanently  
damaged (shorted). The dielectric breakdown voltage is approximately  
8 - 10 kV per cm of contact spacing for materials with this type of  
reverse characteristic. Photocells have 0.16 - 0.5 mm electrode  
spacing so the maximum voltage ratings typically fall into the 100 - 300  
volt range.  
Figure 5. VTL5C3 Life Test.  
The high voltage capability of photocells suggests their use as the  
series pass element in a high voltage regulated power supply. Voltages  
up to 5 or 10 kV can be regulated but the current should be limited to 1  
or 2 mA. The isolated input element greatly simplifies the circuit design  
and the single output element avoids the need for voltage and current  
sharing components.  
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