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DC−DC Buck/Boost Converter
Buck/Boost converter
This circuit is more unforgiving than the boost converter, because the MOSFET and diode voltages and currents are higher
• Before applying power, make sure that your D is at the minimum, and that a load is solidly connected
• Limit your output voltage to 90V
KVL and KCL in the average sense
Interestingly, no average current passes from the source side, through C1, to the load side, and yet this is a “DC - DC” converter
Inductor L1 current rating
During the “on” state, L1 operates under the same conditions as the boost converter L, so the results are the same Inductor L2 current rating
MOSFET and diode currents and current ratings
Output capacitor C current and current rating
Series capacitor C1 current and current rating
Series capacitor C1 current and current rating
Worst-case load ripple voltage
Worst case ripple voltage on series capacitor C1
Voltage ratings
• Diode and MOSFET, use 2(Vin + Vout)
• Capacitor C1, use 1.5Vin
• Capacitor C, use 1.5Vout
Continuous current in L1
Continuous current in L2
Impedance matching
Impedance matching
Thus, the buck/boost converter can sweep the entire I-V curve of a solar panel
Example - connect a 100Ω load resistor
With a 100Ω load resistor attached, raising D from 0 to 1 moves the solar panel load from the open circuit condition to the short circuit condition
Example - connect a 5Ω load resistor
BUCK/BOOST DESIGN