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Hot!MCLV-2 Dev board clarifications

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microLearner
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2021/01/15 20:58:35 (permalink)
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MCLV-2 Dev board clarifications

I am referring to the MCLV-2 board. I have few confusions in the bootstrapping circuit created with IR2181. I know it tries to keep the Gate voltage of Q5 higher than DC+ in order it make the MOSFET Q5 completely ON. How it does is, what i have confusion.
Q1. I do not understand the relation of voltage VHO with respect to VB and VS.
Q2. Simple explanation of the mechanism happening is
a. When Q6 is OFF the capacitor C37 will be charged to 15V - Voltage drop on diode D9(0.7V) = 14.3V?
b. When Q5 is ON, I clearly do not understand the sequence of operations. Please explain.

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    microLearner
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    Re: MCLV-2 Dev board clarifications 2021/01/16 07:00:38 (permalink)
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    Ok, I did some study please correct me if i am wrong.
    1. The gate voltage of Q5 should be greater than the source voltage for Q5 to be "ON", I am not sure how much it should be?
    2. If Q6 is "OFF", the point M1 will be at ground potential. The capacitor C37 will get charged to (15V - Voltage drop on D9). If i assume the voltage drop on diode as 0.7V then the capacitor C37 charges to 14.3V.
    3. When Q5 is "ON", the voltage DC+ will be applied at M1. The voltage at VB = V(C37) + DC+.
    4. As VB > +15V D9 is "OFF", the capacitor cannot discharge, the voltage on Capacitor remains at 14.3V.
    5. The voltage at HO is the voltage present at VB based on the internal design of IR2181. Hence V(HO) = VB = V(C37) + DC+.
    6. Since V(HO) is greater than the source voltage of Q5, the MOSFET Q5 is permanently "ON".
    Is my understanding correct? Please correct if wrong.
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