02-12-2016, 02:54 PM
(02-12-2016, 02:42 PM)Terry Wrote: Reducing the input to the normal voltage of a dry cell - 1.4V - will produce an output of 15.4V with R2 = 100kΩ.
No need to change the resistor. We have a thing called negative feedback!
The fact that Vin is not part of the equation is also a strong clue.
This is a pretty standard boost converter. Usually the switching frequency is fixed and the duty cycle varied accordingly to regulate the output voltage. But this one uses a fixed off time, so the frequency varies according to input voltage. Note how the output current also isn't a factor in the equation, but this assumes "perfect" components. In practice, small variations in duty cycle (on on-time here) with load current are seen because of losses in the components.
