I'm trying to analyze a boost converter circuit. I have all the specs for the inductor used, including inductance (6.8uH) and saturation current (1A). This runs from a 3V supply. I'm wondering if there is a formula for the maximum power than an inductor with a certain inductance and saturation current can transfer when operated from a fixed supply voltage, regardless of at what frequency/duty cycle it is being driven? In other words, what is the theoretical maximum power of a boost converter using that particular inductor and running off of 3V?
The boost converter in this case is usually operating in discontinuous mode, but apparently may switch to continuous mode some of the time.
Best Answer
With a fixed supply voltage and a fixed inductance and a known saturation current, you not only have the maximum energy that the coil can store:
$$E = 0.5 I_{sat}^2 L$$
but also how long it takes to charge the coil with that amount of energy:
$$t_{charge} = \frac{I_{sat} L}{V_{supply}}$$
The power transferred is equal to the energy per cycle divided by the cycle period, \$t_{charge} + t_{discharge}\$.
The discharge time depends on the output voltage, with higher voltages giving shorter times, but in any case, the total period cannot be shorter than \$t_{charge}\$, so this puts an upper limit on the maximum power transfer.
Continuous conduction mode does not change this; while it allows higher switching frequencies, the energy transferred per cycle is proportionally less.