A zero crossing detector identifies when an input signal crosses the zero voltage level, allowing it to switch outputs between high and low states. It functions as a comparator, can be constructed with operational amplifiers or opto-couplers, and is used in various applications such as phase meters and motor speed controls. The document describes both inverting and non-inverting configurations of the detector circuit.

1. What is Zero crossing detector
(Zero cross detector circuit, working and applications)
A guide by Aman bharti (www.circuitspedia.com)

2. Zero crossing detector detects how many times the input
signal crossed the Zero value or Zero voltage level. Zero
cross detector is basically a comparator circuit that compares
the input sinusoidal signal or Sine wave signal with the zero
voltage level, In other words, we can say that this detects the
voltage changing from positive level to negative level and
negative level to positive level. The output of the zero-cross
detector changes when the input voltage crosses the zero level
to High or High to zero.

4. A Zero cross detector compares the input signal with the zero reference voltage
(Vref). It changes the output Either +Vsat or –Vsat by switching from LOW to HIGH
or Vice versa. When the input crosses zero reference voltage. when the input
voltage signal is even a little higher or Lower than 0v the output will quickly
change. A zero-crossing detector can be made using a general-purpose
operational-Amplifier, Using Opto-coupler or using transistors.

5. Zero crossing detector circuit using op amp LM741

6. NON-Inverting Zero cross detector
If Reference voltage zero set on the inverting input terminal
means the inverting terminal is grounded and Input signal
applied at NON-Inverting terminal. +Vcc are connected with
pin 7 and -VEE with pin 4, 6 is the output pin is and a load
resistor RL connected with output to ground, even a little
amount of input voltage in higher than zero (Reference
voltage), then the output will HIGH. When the input goes on
increasing from zero to positive then the output voltage goes
into Positive saturation.

8. Zero cross detector is also called sinewave to square wave converter
This Output is called +Vsaturation .

9. Inverting Zero cross detector
If input voltage applied at the Inverting terminal and reference voltage are
given on NON-Inverting terminal or Non-inverting terminal is grounded,
when even also a little amount of input voltage is higher than zero volts
the output will switch to LOW. When the input goes on increasing from
zero to positive then the output voltage goes into Negative saturation.
And this LOW output is called –Vsaturation.

14. Zero-cross detector using optocoupler
In the circuit of zero crossing detector using optocoupler, we used 1 full-
wave rectifier and the positive dc supply of bridge rectifier connected to
cathode pin of optocoupler input. Output is connected with the collector
pin of the optocoupler. Here full-wave bridge rectifier used without the
filter capacitor. The emitter pin of the optocoupler is connected with the
DC ground. VCC connected with the collector pin. A resistor connected
with a collector is also called a Pull-up resistor.

17. Uses of zero cross detector (ZCD)
● ZCD as Phasemeter
● ZCD as Time Marker Generator
● AC power controllers
● Induction motor speed control and soft starters
● Thyristor firing angle control using Arduino etc
· LOGIC GATES
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Also read
· Sample and Hold circuit

18. Thank you
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