817 CTR 50 - 600 <-- I have
817A CTR 80 - 160
817B CTR 130 - 260
817C CTR 200 - 400
817D CTR 300 - 600
817X CTR 100 - 200 <-- original
817Y CTR 150 - 300I was thinking about measuring the CTR but wasn't sure if the operating point while measuring should be matched with the conditions of the circuit.If you are comparing with the 817X, you need to match the 817X test conditions.
According to the PC817X datasheet: https://www.farnell.com/datasheets/73758.pdf (https://www.farnell.com/datasheets/73758.pdf)For EL817 "X" is a CTR grade and it's a direct substitute of PC817 (that has no X CTR grade), PC817X is a different part that is rated for higher voltage and is an equivalent of EL817-G. Although it does not matter which one is used in this particular circuit.
the CTR @ Vce=5V, If=5mA is 50% to 600%
According to the PC817 datasheet: https://www.digikey.com.au/en/htmldatasheets/production/34186/0/0/1/pc817-series (https://www.digikey.com.au/en/htmldatasheets/production/34186/0/0/1/pc817-series)
the CTR under the same conditions is: 50% to 600%
This is for the non graded versions, the PC817X has a Vceo=80V and the PC817 has a Vceo=35V, that is the difference and that is important to prevent failure due to excessive voltage.
According to the PC817X datasheet: https://www.farnell.com/datasheets/73758.pdf (https://www.farnell.com/datasheets/73758.pdf)For EL817 "X" is a CTR grade and it's a direct substitute of PC817 (that has no X CTR grade), PC817X is a different part that is rated for higher voltage and is an equivalent of EL817-G. Although it does not matter which one is used in this particular circuit.
the CTR @ Vce=5V, If=5mA is 50% to 600%
According to the PC817 datasheet: https://www.digikey.com.au/en/htmldatasheets/production/34186/0/0/1/pc817-series (https://www.digikey.com.au/en/htmldatasheets/production/34186/0/0/1/pc817-series)
the CTR under the same conditions is: 50% to 600%
This is for the non graded versions, the PC817X has a Vceo=80V and the PC817 has a Vceo=35V, that is the difference and that is important to prevent failure due to excessive voltage.
Oh, an BTW the imaginary current path that "damaged the optocoupler" is absolutely wrong, and circuit is similar only on a first uneducated glance. LD7552 and OZ531 are not alike at all. On pin 1 there is a very high resistance voltage divider for voltage sense. And There still won't be enough current to destroy optocoupler through resistors on HV pin as well (EDIT: unless there is no resistor like on reduced application diagram). What most likely happened was that MOSFET got destroyed for some reason and PWM controller got destroyed by high voltage coming from MOSFET gate, and destroyed optocoupler through the IC (if it's actually bad, which I now doubt). Also check if MOSFET source resistor to GND did not fail open, it happens very often with such failures.
and that's why I ordered NCP1207A ICs.There are loads of OZ531TG1N on aliexpress. Why in hell would you order some substitute? NCP1271A is simply not suitable due to different operation frequency.
https://www.aliexpress.com/item/4000150942652.html (https://www.aliexpress.com/item/4000150942652.html)
In addition it can be directly replaced with NCP1203, NCP1271 (1271P65) and FA5571N.".Neither of those are equivalents of each ater and cannot be used interchangeably without circuit modifications, and NCP1207 being the least similar to the rest.
I couldn't find a reliable source and there wasn't any OZ531TG1N only listingsYou should chose "Color" to select correct item if there are multiple in the listing. Not to say there are plenty single item listings https://www.aliexpress.com/item/4001116474991.html (https://www.aliexpress.com/item/4001116474991.html)
so I started searching for the equivalent of OZ531TGN and I found this page:Schematic looks like someone replaced different part number with OZ531TG1N. Pin 1 name does not match with other sources, pin function table above the schematic is for something very different, and does not match with schematic and pinout above it, looks similar to NCP1207.
https://www.520101.com/html/circuitry/1228042826.html (https://www.520101.com/html/circuitry/1228042826.html)
There are loads of OZ531TG1N on aliexpress. Why in hell would you order some substitute? NCP1271A is simply not suitable due to different operation frequency.
Neither of those are equivalents of each ater and cannot be used interchangeably without circuit modifications, and NCP1207 being the least similar to the rest.
It probably can be replaced with NCP1271B, however circuit on pin 1 will need to be modified. It probably has different Vcc (that you cannot adjust without rewinding transformer), and it probably has a different threshold voltage on current sense pin, that would need drain resistor value change. But it's not possible to know if modification is needed as there is no datasheet for OZ531 to know original specs. I never trust equivalents listed on internet, they are plain wrong more than 50% of the time.
Schematic looks like someone replaced different part number with OZ531TG1N. Pin 1 name does not match with other sources, pin function table above the schematic is for something very different, and does not match with schematic and pinout above it, looks similar to NCP1207.
Where can I see that pin 1 of OZ531TG1N has a different function compared to pin 1 of NCP1207A that I ordered?
I can't find which is operating frequency of OZ531TG1NIn my 3rd and 4th posts. Pin 1 is VINS.
Every OZ531TG1N I saw either had zero reviews or the IC had 8 pins or it had only one row of text as it isn't original.Part of text/logo removed does not mean anything. It's a very common practice on aliexpress and is done with both original and fake parts. Not to say there is much higher chance receiving counterfeit ON semi part than O2Micro part. And frankly I don't even trust positive reviews. Most of them are left even before checking the part, and the rest say that obvious counterfeit (obvious for me) they bought is good. The only feedback I usually trust is negative.
In my 3rd and 4th posts. Pin 1 is VINS.
>https://www.eevblog.com/forum/projects/how-critical-is-optocouplers-ctr-parameter-in-smps-feedback/msg5365073/#msg5365073 (https://www.eevblog.com/forum/projects/how-critical-is-optocouplers-ctr-parameter-in-smps-feedback/msg5365073/#msg5365073)
Part of text/logo removed does not mean anything. It's a very common practice on aliexpress and is done with both original and fake parts. Not to say there is much higher chance receiving counterfeit ON semi part than O2Micro part. And frankly I don't even trust positive reviews. Most of them are left even before checking the part, and the rest say that obvious counterfeit (obvious for me) they bought is good. The only feedback I usually trust is negative.
Suffix most likely means means packaging and nothing else. Very unlikely that suffix would change functionality to the amount of pin function change. Chinese web page that says they're equivalents cannot be trusted as it lists 4 verifiably incompatible ICs as equivalents and provides wrong pin function table.
I know there is a risk. However, the pinout of NCP1271A from this datasheet (https://pdf1.alldatasheet.com/datasheet-pdf/download/166534/ONSEMI/NCP1271A.html) exactly matches the connections on the PCB. The note in the datasheet says pin 1 must be connected to GND through the resistor and that is exactly as on the PCB. And everything else matches that datasheet.Does it really have parallel RC circuit from pin 1 to GND and nothing else connected? And again, beside other things similar PWM controllers have different VCC and threshold voltages.
Does it really have parallel RC circuit from pin 1 to GND and nothing else connected? And again, beside other things similar PWM controllers have different VCC and threshold voltages.Yes, there is a 43k resistor from pin 1 to GND and C907 capacitor in parallel to the resistor. Although the capacitor is unpopulated from the factory. You can see that missing C907 capacitor in the second picture from my very first post too - the one between the MOSFET that I removed and the 450V capacitor.