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To turn on N-MOSFET (high side) what should be the gate voltage (Vgs) in buck converter before turn on and after turn-on of MOSFET.

Case 1 (As per my understanding): To turn on the MOSFET the gate voltage should be greater than Vs (MOSFET source) + whatever the MOSFET needs to turn FULLY on. But when the buck converter is operating in DCM I want to know what will be the node voltage of the Vs (MOSFET source) so that my gate voltage should be greater node voltage by using the bootstrap driver circuit.

-In DCM it forms a closed loop with the ground (inductor -> load -> ground) because the diode is in reverse bias. (Am I right or wrong?)

-In CCM diode will be conducting (Vs) node will be approximately with reference to the ground

Case 2 (As per my understanding)-To drive the MOSFET the gate voltage required is (Vin+whatever the MOSFET needs to turn FULLY on) after turn on because after MOSFET turn on the Vs node potential will be Vin.

Kindly correct me if am wrong in understanding.

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DATTU SAMPATH KUMAR P
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  • Case 2: The Vs node will be less than Vin due to Rdson and the current flowing. Thus the gate voltage should still be Vs + Vth. – Kartman Nov 23 '21 at 10:55
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    It should NOT be Vs+Vth - that's the biggest beginner mistake. It should be Vs+whatever the MOSFET needs to turn FULLY on ... choose the Vgs value at which RDSon is measured (and that's usually more than double Vth) –  Nov 23 '21 at 12:03
  • @user_1818839 you are right, here my intention of this question is to focus more on Vs node voltage. – DATTU SAMPATH KUMAR P Nov 23 '21 at 19:22

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