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[SOLVED] SMPS Circuit design for 4.5v with Optocoupler tied to + rail First ?

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Deltatango

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I have got a cheap SMPS power supply with an output of 4.5V based on the TNYxxxx range of IC's at about 1A which has become faulty.

It has got a very small component a 6pin smd device marked M801 or E506 which I am searching for in other forums to find out what it is, I have looked at many markings but as its a Chinese part who knows.

So decided to think outside the box a bit, now other than "clever" supplies which use otput monitor type IC's, a basic format is an optocoupler and TL431 with resistors. I have seen on 5v supplies a zener (2 to 3v) used to "stabilize" things with an optocoupler (I figure that at that low woltage there is not enough "spare twitching" room to regulate well with 2.5v on a TL431 and forward voltage with an optocoupler diode).

Now this supply uses an optocoupler First tied to the + rail via a 82R resistor then via this "?" chip to ground, I have got plenty of circuits with it in a normal position (ground side) but have failed to find any used this way round with a Low voltage <5v supply output.

I know my poor old internet is on a old bad telephone line but when I have got to AliExpress to find some component suppliers and link with those to ask my line goes down which is a great help??

It can't be that complex but yet has what looks like a couple of feedback corrections for frequency response control, so that makes me think its an OP amp input type with a mosfet output design

Can you help show me some circuits which might help me to find that chips identity please..........

Thanks from David
 

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It sounds like its the opamp error amplifier...but i think you already guessed that....as attached
 

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Yes thats what I am thinking of, or some similar device with an OP amp and reference diode combo built in. Thank you for your drawing it may jog some thoughts.

David
--- Updated ---

Made a partial breakthrough with searching for variant OP amps found a NCP4300A which is heading in the right direction but just need a possible 6pin version so maybe a with single amp device. Tried searching for it but just keep getting how to make an OP amp work on a single supply gets frustrating not finding a good search parameter.

Fingers crossed some person can help me.

David
 

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Cracked it I hope its a TSM1051CLT marked M801 and the pin outs match with what I am looking at.

Thanks to those who helped........

David
 

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