The primary output capacitor, C_OUT1, can be selected using either Equation 14 or Equation 15. For this design, an output voltage ripple of 5 mV and a load transient of 0.2 V is used. From this, a ripple current of 0.34 A at 60-V input, and a peak transformer current of 0.77 A at full load is calculated. The two output capacitor equations give values of 11 μF and 5 μF. Because of the large derating of ceramic capacitors, C_OUT1 = 1 × 22 μF is used. Keep in mind that the equations give the minimum capacitance value and in no case should the capacitance of C_OUT1 be less than 2.2 μF. More output capacitance can be used to improve load transient response. Also note that when using type 3 ripple injection, the actual ripple voltage appearing on the output can be kept small.

where

• I_PK = peak transformer current from Equation 13
• ΔV_O = output voltage load transient

where

• ΔI = ripple current from Equation 12
• V_ripple = ripple voltage on primary output

C_OUT2 is selected using Equation 16. In this case, a ripple voltage on the secondary otuput of 20 mV is chosen. The minimum input voltage must be used in this equation. A value of 10 μF is calculated and 1 × 22 μF for C_OUT2 is selected. Again, the equation gives the minimum capacitance value and in no case should the capacitance of C_OUT2 be less than 2.2 μF.

Both output capacitors should be X7R ceramics in a 1206 or 1210 case size, and rated for at least twice the output voltage.