Hello,
For AC inputs a full bridge rectifier is used as shown in the below datasheet graphic.
When the AC input is on, the input will drive the rectifier on both the positive and negative cycle of the AC wave. The signal will be DC after the rectifier. Any ripple after rectification can be ignored since improper signaling will be prevented by the voltage thresholds.
The input thresholds are set by Rtht and Rsense. Please see section 9.2.1.2.4 - "Designing for Input Voltages Greater Than 60 V" - and How to Design Isolated Comparators for ±48V, 110V and 240V DC and AC Detection (Rev. A) for more details.
Best,
Andrew
As shown in the figure, even when the AC waveform is on, the output of "ISO1212" will repeat on and off.
If you do so, the output of "ISO1212" will be turned off even when it is normally turned on.
Is there no other way than to lower the threshold and reduce the off time?
What kind of measures do you usually take?
Thank you for your reply.
Hello,
Thank you for the diagram and clarification of the question. I understand that you are concerned about the output flickering as the rectified AC signals drops low. The Capacitor Cin should be sized large enough to smooth the ripple to a desirable level that will not cross the input thresholds set by Rthr and Rsense.
I hope this helps.
Best,
Andrew
The above is a reference circuit provided by TI. The capacitor value is 1nF. If you run a simulation with this value, the ripple will hardly disappear and it will be in an OFF state. Isn't the reference material recommended? Are there any recommended capacitor values? Thank you for your consideration.
