*Volts per second*, or *dV/dt*, is the rate at which voltage is changing. Digital IC output drivers are often specified for slew rate in volts per nanosecond. For example, 5 V/ns. MOSFETs are often specified for maximum Drain dV/dt. For example, 50 kV/us. This tells us the maximum drain voltage rate of change before the MOSFET is turned on by the high dV/dt.
And we can't forget the all important formula *i = CdV/dt*. This is the current i through capacitance C when the voltage across the capacitor is changing as dV/dt.
While we are talking about dV/dt let's look at *di/dt* as in *V = Ldi/dt*. This tells us the voltage V across inductance L as the current through it is changing as di/dt.
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The *volt-second product* is equal to the average voltage applied to a device for some time period; voltage is integrated over time. Transformers often have a maximum volt-second specification that tells us when the transformer core reaches a certain level of saturation. For example, a 240 V sine wave, 50 Hz transformer must support a volt-second product of 2.16 volt-seconds. Note that the voltage-second product is calculated using the average voltage of 216 and not the RMS voltage of 240.
