SNVS788H January 2012 – August 2021 LM5019
A simplified waveform for secondary output current (IOUT2) is shown in Figure 8-7.
The secondary output current (IOUT2) is sourced by COUT2 during on-time of the buck switch, TON. Ignoring the current transition times in the secondary winding, the secondary output capacitor ripple voltage can be calculated using Equation 25.
For a 1:1 transformer turns ratio, the primary and secondary voltage ripple equations are identical. Therefore, COUT2 is chosen to be equal to COUT1 (1 µF) to achieve comparable ripple voltages on primary and secondary outputs.
If lower output voltage ripple is required, a higher value must be selected for COUT1, COUT2, or both.