Powering 33063 Buck Regulator near its Vmax
Output power: 5V x 0.35A = 1.75W. Estimated efficiency is %85, so the required input power is 1.75 / 0.85 = ~2W. At 38VDC, input current is 2W / 38V = ~55mA. After rectification and filtering, if you get 40VDC then you can place a resistor with a value of RS = (40-38)/0.055 = 36R (Place 39R). Power dissipation of this serial resistor is about PR = 39 x 0.055² = 0.11W. So you can put a 39R/0.25W resistor. You can also make a simple RC low-pass filter by putting a 220uF elco after this resistor to filter-out some ripple.