TIDA-010081: Detailed calculation of ACSNS detection circuit of UCC28180

Hi Links,

This circuit is sampling the peak rectified AC voltage (this is why D6 is used). The voltage on C18 will represent the peak rectified AC voltage multiplied by the resistor divider ratio minus the forward voltage drop across D6. The purpose of C18 is to hold the sampled peak voltage value across the 1/2 AC line cycle. R18 is used to slowly bleed off the voltage on C15 so that if the AC line voltage drops, the voltage on C18 will be updated appropriately.

Best Regards,

Ben Lough

Thank you for your reply, but the actual situation is a little different from what you described, we see that D4 and D5 have completed full-wave rectification before D6, D6 does not play the significance of rectification, through simulation we can find that if there is no D6 and R15, then the voltage of C18 will be reduced by about 0.6V.

I have a general understanding of the design idea of this circuit, and I want to have a more detailed calculation process or design process to explain this circuit, which is convenient for users to accurately design and calculate such circuits, so that it can be applied in more occasions