How to Select a Transformer for an Isolated Buck Converter (Download)

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An isolated buck topology (Fig. 1) is similar to a generic buck converter. By replacing the inductor in a buck circuit using a transformer, we can get an isolated buck converter. The transformer’s secondary side has an independent ground.

During on-time, the high-side switch (QHS) is on and the low-side switch (QLS) is off. The transformer’s magnetizing inductance (L_PRI) is charged up. The arrows in Figure 2 show the current flow direction—the primary current increases linearly. The current ramping slope depends on (V_IN – V_PRI) and L_PRI. The secondary-side diode, D1, is reverse-biased during this time interval and loads current flow from C_OUT to load.