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Working of this circuit - Diodes

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I have the below circuit where a single Phase AC input is given between Line and neutral.

enter image description here

But I have two questions:
  1. Can someone tell me the working of this circuit and at what time the WEILD_DET pin will be active low?
  2. The WEILD_DET pin goes into an MCU. There's no other description or instance of this in the schematic.
The application of this design is an EV Charger. I tried to relate the word "Weild/weld/wield" with the application of EV but didn't get any results.
Can someone help?
 

Its a zero crossing detector. C40 and R52 limit the current that can flow, the four diodes make a bridge rectifier so both polarities of the AC appear as the same polarity and the LED inside U12 lights whenever sufficient current flows. When it lights, U12's transistor conducts and pulls it's collector voltage low.

The idea is it gives an indication of when the AC line voltage is close to zero (hence the name "Zero Crossing Detector" or sometimes ZCD. Any time when there is sufficient AC voltage, regardless of polarity, to light the LED the transistor will conduct, the result is a brief high pulse on "WEILD_DET" as the AC cycle passes through zero on its way to the opposite polarity.

Brian.
 

Hi,



it´s really not a big thing for you to draw the circuit in a simulator software.

Then you can see all voltages, currents, timings, waveforms....

Klaus
 

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