I'm having a bit of trouble figuring out how to calculate the max voltage an inductor will get to when switching it with a N-channel MOSFET. My circuit is shown below. All it does is turn on the MOSFET for 5us as the inductor current rises to its max value.
RDSon(M1) = Drain source resistance of M1 = 0.012.
V1 = supply voltage of battery = 1v
So max current attainable would be V1/RDSon(M1) = 1v / 0.012Ω = 83A.
The gate of the MOSFET is driven by V2 which is on for 5us then off for the remainder of the time. So the current starts to build through the inductor and never quite reaches its max value of 83A. In fact the MOSFET is on for such a short time I have found out it can be approximated by a linear function:
Imax ≈ V1 * Ton / L
So for my example it would be:
Imax ≈ 1v * 5us / 500uH = 10mA
As you can see from the graph of the circuit below, this is precisely the max current. But I can't figure out how to get the max voltage of the inductor with this value. Any ideas?
To get my value for max current I simply took the inductor voltage equation and assumed the δI/δt could be replaced by ΔI/Δt, as below:
VL = V1 = L * δI/δt ≈ L * ΔI/Δt => ΔI = V1 * Ton / L.
If I could somehow find out how long it takes the max current to go down to zero as marked below, I could use the straight line approximation again and get a ball park value of what the peak voltage will be based on the max current but I can't see where to get that value from.
RDSon(M1) = Drain source resistance of M1 = 0.012.
V1 = supply voltage of battery = 1v
So max current attainable would be V1/RDSon(M1) = 1v / 0.012Ω = 83A.
The gate of the MOSFET is driven by V2 which is on for 5us then off for the remainder of the time. So the current starts to build through the inductor and never quite reaches its max value of 83A. In fact the MOSFET is on for such a short time I have found out it can be approximated by a linear function:
Imax ≈ V1 * Ton / L
So for my example it would be:
Imax ≈ 1v * 5us / 500uH = 10mA
As you can see from the graph of the circuit below, this is precisely the max current. But I can't figure out how to get the max voltage of the inductor with this value. Any ideas?
To get my value for max current I simply took the inductor voltage equation and assumed the δI/δt could be replaced by ΔI/Δt, as below:
VL = V1 = L * δI/δt ≈ L * ΔI/Δt => ΔI = V1 * Ton / L.
If I could somehow find out how long it takes the max current to go down to zero as marked below, I could use the straight line approximation again and get a ball park value of what the peak voltage will be based on the max current but I can't see where to get that value from.
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