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What is this circuit

VTI_16V

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I got this board for repair and i am not sure am I crazy or am I missing something here? The component that is missing is FDS6680 mosfet.. I removed it because it was in short circuit. But when i tried to figure out what that mosfets does I was scratching my head... So I marked 12V coming from supply, over schottky diode, through coil... And this mosfet is connected to that same coil switching ground and making a short circuit? That same coil is connected to the 12V supply, what is this circuit, I can not wrap my head around this?
 

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betwixt

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Looks like a standard SMPS boost configuration. Incoming current passes through the coil and gets connected to ground when the MOSFET is conducting. In other words the supply is connected across the coil. When the MOSFET is turned off, the collapsing magnetic field in the coil conducts through the Schottky diode to the power output. By switching the MOSFET on and off rapidly (10s of KHz usually) and controlling the switching waveform it is possible to regulate the output voltage.

Brian.
 

VTI_16V

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Thanks for great explanation. Do you maybe know what is this small 8 pins component that is connected to the gate of mosfet? It says MTRP S148 on it, but I can't find anything with thoose marks?
 

betwixt

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I'm afraid there are hundreds of SMPS controllers and as far as I know, no master list of their device codes. The best you can do is try the major manufacturers product selectors and look at data sheets individually.

Brian.
 

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