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Single-ended primary-inductor converter (SEPIC) is a type of DC-DC converter allowing the electrical potential (voltage) at its output to be greater than, less than, or equal to that at its input; the output of the SEPIC is controlled by the duty cycle of the control transistor.
A SEPIC is essentially a boost converter followed by a buck-boost converter, therefore it is similar to a traditional buck-boost converter, but has advantages of having non-inverted output (the output has the same voltage polarity as the input), using a series capacitor to couple energy from the input to the output (and thus can respond more gracefully to a short-circuit output), and being capable of true shutdown: when the switch is turned off, its output drops to 0 V, following a fairly hefty transient dump of charge.
By varying the duty cycle of the mosfet we can increase or decrease the DC input voltage by a factor of D/(1-D) (where D is the duty cycle). In the example we have set the duty cycle at 33.3% so with 10V at the input we expect that after the transients settle out to have 5V at the output.
If you want to change the duty cycle just change the
width of all voltage pulse sources (3.33% is 33.3% duty cycle and 10% is 100% duty cycle).
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