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The design uses a CUK topology with an LM3488 controller. LM3488 uses a fixed frequency (400KHz) PWM current mode control architecture. Peak current through external FETs Q1 and Q2 is sensed by the controller through an external sense resistor - Rsen.
CUK topology provides low input and output ripple due to the use of input and output inductors. Blocking capacitor C5 also provides capacitive isolation from input and output as well as protection from switch failure. CUK converter performs DC-DC conversion function similar to buck-boost converter. It can either increase or decrease the magnitude of the output voltage and provide inversion of output polarity.
Theory of operation:
CUK converter operates via capacitive energy transfer. The capacitor C5 is connected to the input source through the input inductor L1 (coupled inductor) and stores the energy from the source. When switches Q1/Q2 are ON the stored energy in capacitor C5 is released to the output via output inductor L1 (coupled inductor).
Notes:
1. L1 is a coupled inductor.
2. Please note that the LM321 op-amp "A1" in the schematic is designated as "U" in the board layout.
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Example Schematic Showing Connection for all Components.
