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Switching of power supply using optocoupler

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Basic concept is to have a isolated feed back from output to switch


Normally they are use on switching power supply to send back to the main switching transistor the turn on and turn off signal, on this way you will have a isolation between the input ( mains ) and the output voltage, The high frequency transform will send the energy from primary to secondary, and the optocoupler will send a isolated feed back to the main "switch" to turn on or off the power transistor on high tension side
 

Please explain me this, following diagram ....
2.jpg
 

The Ac input is tyarnsformed in CC bt the bridge rectifier and the Capcitor, This CC voltage will be turned on and off on high frequency transformer by the Fet inside the TOPSwitch-GX. This hifh frequency switch will be trasfered from primary to secondory off the transformer, The secondary will rectifield and filtred, the voltage output will be sampled by the TL431 that will trun on and off the feedback led inside the optcoupler, After that the photo transistor inside the optcoupler will feed the Control input on TOPSwitch-GX, and they will adjust the frequency / dutycilce to have a stable CC output. This circuit ist's a very standard switch power supply
 
Dc is the correct ( CC is on my natural lanquage Pt ), the use off the sampling is to mantain the output at the desired level, They read the output ( sampling ) and tell the controler via led feed back, what is there, the nthe controler take acition to increase / decrease or mantain the actual power.
 
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