CrazyEngineers
CrazyEngineers

  • Urgent help please--need to make sense of a circuit

    preeste

    Member

    Updated: Oct 26, 2024
    Views: 1.0K
    Hey there guys. I need some help to understand the circuit attached and how it functions. This circuit is a zero-crossing detector and its output is connected to a microcontroller pin (the pin is an input). It takes a 230V ac signal and I assume somehow gives a 5V or a 0v signal when there is a zero crossing or no zero crossing. Can someone please explain how this works and what the output of the circuit will be. Thank you so very much. I am really confused and need some help. The zener diodes used are 5.1V diodes.

    Its really really really urgent!!!!😔

    Here is the link to the circuit:
    #-Link-Snipped-#
    0
    Replies
Howdy guest!
Dear guest, you must be logged-in to participate on CrazyEngineers. We would love to have you as a member of our community. Consider creating an account or login.
Replies

  • reachrkata

    Member • Nov 11, 2009

    This is how I understood the circuit -

    1) R1-C1-D1-D2 form a clipping circuit such that, before diode D3, we get a clipped sine wave of +5V to -5V p-p waveform.
    2) R3-Q1-R4 acts as the inverter for this wave and we get a 0V-5V signal at Collector of Q1 corresponding to +5V -5V at the base. Note that D3 prevents the negative part. Strictly speaking D3 is unnecessary because the transistor itself would take care of that.
    3) R7-Q2-R8 inverts this once again so that the 5V-0V signal here is in phase with the +5V -5V input to Q1.
    4) Both these out-of-phase signals are given to CR circuits which act as differentiators giving -ve and +ve pulses at the corresponding edges of both signals.
    5) These Pulse waveforms are combined using the OR logic via diodes such that only the positive going pulses of both waveforms add and pass through to Q3. Note that the pulses coming here correspond to the Zero-crossings of the +5V -5V signal.
    6) Q3 is in inverter configuration such that, at its collector, there is 5V whenever the AC signal is above/below 0. It gives a short pulse of 0V at the zero crossover regions.

    Hope this clarifies !

    -Karthik
    😁
    Are you sure? This action cannot be undone.
    Cancel
Home Channels Search Login Register