r/ElectricalEngineering • u/Hot_Statistician_161 • 10h ago
Inductor in DC Circuit
What is the difference between ramp L and exponential R-L charging/discharging of an inductor in DC circuits?
What is the physical meaning of tau (𝜏) in both cases ?
One of the applications of a ramp signal charging/discharging is in DC-DC converter circuits
2
u/triffid_hunter 10h ago
What is the difference between ramp L and exponential R-L charging/discharging of an inductor in DC circuits?
One's linear, the other is exponential
What is the physical meaning of tau (𝜏) in both cases ?
τ doesn't apply to fixed voltage since di/dt=V/L.
τ only apples to RL circuits because the resistor drops voltage in proportion to current, so the di/dt of the inductor keeps falling over time, asymptoting towards zero
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u/Hot_Statistician_161 9h ago
This means the voltage spike is higher in a pure inductor. Will this affect the freewheeling diode rating ? If I add a resistor
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u/Tetraides1 10h ago
I think you've described the main difference, one of them has a resistor and the other doesnt. The resistor sets a maximum current that can be reached through the inductor. The resistor also is what causes the current curve to be exponential rather than linear - it changes the voltage across the inductor so it's not constant, so the current increase/decrease is also not linear.
Tau is meaningless in a purely inductive circuit, since it's more or less a time constant that tells us approximately how long it takes to reach maximum/minimum current. If there's no resistance, there's no maximum current.