I just pulled a 4N37 out of my junk box to use. Non-critical usage; all should be fine.
To get the pin-out I downloaded a datasheet from Vishay. Looking at that, I don't see any difference in specs between 4N35, 4N36 and 4N37. There must be something different. Did I miss something obvious? What makes them different?
Fairchild's datasheet is the same.
-- Bill Sloman, Nijmegen
The have different current transfer ratios and different voltage ratings. Check page 3 of the Vishay PDF. Bob
The tables have row entries for the different versions, but as far as I can see, the numbers are all the same for 35, 36, 37.
The isolation leakage current test is;
short terminals 1 and 2 (input). short terminals 4, 5 and 6 (output). place several kV across the input - output and measure the voltage at which the lekage current is 100uA.
The 1983 Motorola data sheet gives the following results;
4N35 Vio = 3550Vpk 4N36 Vio = 2500Vpk 4N37 Vio = 1500Vpkand that's the difference.....
--- From the 1996 QT Optoelectronics Data Book:
The input-to-output isolation voltages with 100µA of input-to-output leakage current.
The 4N35 is rated for 3550VAC, the 4N36 for 2500VAC, and the 4N37 for 1500VAC, all peak.
In addition, the pulsewidth of the high voltage waveform is 8ms, (I guess that means a half-cycle of rectified 60Hz.??) and the input terminals (diode) are shorted together and the output terminals (transistor) are shorted together.
-- John Fields Professional Circuit Designer
Interesting.
The Vishay datasheet has this general statement at the beginning: "These couplers are Underwriters Laboratories (UL) listed to comply with a 5300 VRMS isolation test voltage."
In the later table sections there is one entry for 'Isolation test voltage' at 5300 V-RMS.
I guess I would take that to mean that there is no longer a difference between what is manufactured for those three part numbers.
Not important for what I am doing now, but I was curious. Thanks to Ross and John for the information.
There were differences when these part numbers were first introduced into the industry long ago, apparently mostly with isolation, but since then the VDE and IEC safety isolation testing standards have changed due to better understanding of high voltage isolation performance, failure mechanisms of the dielectric materials, and scientifically sound and reliable methods of testing that performance. Looks like they're using a destructive test on lot samples as well as nondestructive testing applied to 100% of production output with a new "partial discharge" criterion in the picoampere region- the trick there is to perform the nondestructive 100% lot testing without introducing permanent component damage. There is a good safety testing app note on their site to this effect. Vishay has that whole family registered to the same UL and VDE safety standards, and the abs max and electrical performance are the same for each, so they must be maintaining the separate part numbers for replacement purposes, unless there is a distinction to be made in those cryptic options they have. You really don't know what you have in hand unless you can decipher the date code on the package.
Without stating the test conditions which produced the 5.3kV figure I would be dubious that the same figure applies to all three types.
In that case there would be little point in producing 3 part numbers. It would be far simpler to produce only the 4N35 and state that it is a suitable replacement for the other 2 types. My guess is that the goal is to produce a device with the highest isolation possible for the particular process and those which meet that goal are called 4N35 and those which do not are graded as either 4N36 or 4N37. That way they don't have to chuck out the failures... same thing happens with transistors.
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