# Maximum input voltage in buck converter

by AlfroJang80   Last Updated October 19, 2019 20:25 PM - source

Consider the following simple buck converter

It consists of an NMOS input device, a diode, inductor and capacitor and a load. If we are limited to a gate voltage on the NMOS device of 12 volts peak-to-peak, what is the maximum input voltage that we would be able to use with this limitation? Assume a threshold voltage of 3V.Neglect NMOS on-resistance

Here's what I think:

For an NMOS $$V_{GS} >V_{TH}$$ $$V_G - V_S > V_{TH}$$ Neglecting the NMOS on-resistance, we get: $$V_G - V_{in} > V_{TH}$$

Since we have a 12V-p-p signal at the gate, the maximum gate voltage is 6V. Substiuiting this, along with our 3V threshold voltage, I get $$6V-V_{in} > 3V$$ $$-V_{in} > -3V$$ $$V_{in} < 3V$$

Is this correct?

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