Opto isolator current transfer ratio1/1/2024 ![]() The overall efficiency makes it look like a lousy transistor with a minimum hFE of 20% = CTR ( 100% minimum for better grades) HFE of Transistors are also wide tolerance and may be 500% higher than minimum. the PhotoDiodes, PD is very consistent near 0.5 mA/mW at a specified wavelength.LED's might have a 250% to 300% tolerance for radiance above some minimum. ![]() Re: Normalised Current Transfer Ratio which I'm finding quite a bit harder to grasp. ![]() Please supply more application information for further help! I our case with an If of 10mA Vf is ~1.2V To calculate the resistor value on the input you would subtract the forward voltage drop of the diode (Vf) from your drive voltage and divide that by 10mA. For example if Vce needs to be ~1V, you can use figure 6 to see that an If of 10mA will give you an Ic of 50mA with a Vce of ~1V. To answer your question directly, you would start with your desired drive current, 50mA and would need to define the largest acceptable Vce for your application. If so, increasing your If will allow you to drive a 50mA load at a lower Vce. Without knowing your application (drive side voltage and load resistance) I dont know if the Vce would be too high. Possibly something like the LTV-825įrom the LTV-825 datasheet, figure 3, you can see that you can drive a collector current of 50mA with a Vce of ~2V with an input current( If) of 4mA. ![]() If you need 50mA you will need a beefier optoisolator. Per the datasheet, the absolute maximum collector current (Ic) is 30mA. ![]()
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