Transformer design for CY8CLEDAC01 circuits

Question: How is the number of turns in the auxiliary winding determined?




The auxiliary winding provides VCC for the CY8CLEDAC01 device. The turns ratio between secondary and auxiliary windings determines the voltage on the auxiliary winding. A diode DVCC and current limiting resistor RVCC (typically 10Ω to 100Ω) are connected in series with auxiliary winding to reduce the maximum voltage seen on VCC. With maximum output voltage on the secondary, the voltage at VCC pin of the CY8CLEDAC01 must not exceed 16V (VCCMAX).

The auxiliary winding voltage VAUX is typically clamped at 15V, to not exceed the VCCMAX rating of 16V. Therefore, the auxiliary turns is given by: