In my project, I need an under voltage lockout (UVLO) to connect the load electronics to the energy-storage element via a power-gating transistor when the voltage across the supercapacitor exceeds the threshold voltage set by the potential divider circuit connected to the 1.8-V voltage detector and disconnected when the capacitor voltage drops below the minimum voltage threshold signaled by the 1.5-V voltage detector.

How do these three MOSFETs work to connect and disconnect the load, knowing that SI-2377 is a P-channel and PMF280UN is an N-channel?

enter image description here

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    \$\begingroup\$ Do you understand when a MOSFET switches on or off? It has to do with the \$V_{GS}\$ which is the voltage between Gate and Source. The MOSFETs in this schematic are controlled by the XC6120 voltage comparators. You include links to the datasheets of the MOSFETs while not including any information on the XC6120 voltage comparators which detect the voltages. Where does this schematic come from? The right side does not make much sense to me as it appears unable to control anything. Maybe someone removed the connection to the gate of the pass transistor??? \$\endgroup\$ Commented Nov 6, 2020 at 10:51
  • \$\begingroup\$ XC6120N is a detector voltage and the supercapacitors charges by semi actif boost rectifier and voltage multiplier \$\endgroup\$ Commented Nov 6, 2020 at 11:12
  • \$\begingroup\$ XC6120N (torexsemi.com/file/xc6120/XC6120.pdf) is a detector voltage a the charge of the energy storage ( supercapacitors )is done via semi actif boost rectifier and voltage multiplier so I have two question the first is how this system controlled Si_2377 in two Two side? and the second question is what is the conditions to switches si-2377 TURN ON and OFF @cheniour oussama \$\endgroup\$ Commented Nov 6, 2020 at 11:39
  • \$\begingroup\$ @cheniour oussama - Hi, I'm "rolling back" (i.e. undoing) your last edit to the question. By removing the schematic, you made the question impossible to answer, so I'm rolling-back to the previous version, which included that schematic. (Also, your removing of the links to the MOSFET datasheets and reversing helpful grammar edits didn't improve the question either.) You didn't add an "edit reason" when you made that edit, so it's unclear why you did it. I hope it was just a mistake. Please only use edits to improve a question. Thanks. \$\endgroup\$
    – SamGibson
    Commented Nov 6, 2020 at 14:36

1 Answer 1


Well, it doesn't properly work because there is a connection missing. Look closely at the drain of the right-hand MOSFET - there is a black dot that signifies another connection but, that connection is missing: -

enter image description here

Without that connection (I've added it in red dotted lines) the whole right hand side of the circuit is pointless because it doesn't activate or deactivate anything.

  • \$\begingroup\$ thank you but i have 2 question the first is what is the importance of the red line that you added ? and the second question how this three mosfets working if there is not 1.8 volt in the energy storage? \$\endgroup\$ Commented Nov 6, 2020 at 14:02
  • \$\begingroup\$ @cheniouroussama The red line allows the right hand circuit to actually control the main series MOSFET at the top. Without it the right hand circuit does nothing. This circuit relies on the energy storage voltage level being greater than about 2 volts. If it drops below 2.16 volts then it turns off the series MOSFET and implements UVLO. \$\endgroup\$
    – Andy aka
    Commented Nov 6, 2020 at 14:12
  • \$\begingroup\$ @cheniouroussama are you done with this question and answer now? Are there any residual questions that need to be addressed? Can this question be formally closed down by answer acceptance or are you still confused about something? \$\endgroup\$
    – Andy aka
    Commented Nov 17, 2020 at 10:43

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