Question

State any two application of each of following i) Comparator ii) Zero Crossing Comparator

Answer 1

Application of Comparator: 

1. Null detectors: A null detector is one that functions to identify when a given value is zero. Comparators can be a type of amplifier distinctively for null comparison measurements. It is the equivalent to a very high gain amplifier with well-balanced inputs and controlled output limits. The circuit compares the two input voltages, determining the larger. The inputs are an unknown voltage and a reference voltage, usually referred to as vu and vr 

2. Zero-crossing detectors: For this type of detector, a comparator detects each time an ac pulse changes polarity. The output of the comparator changes state each time the pulse changes its polarity, that is the output is HI (high) for a positive pulse and LO (low) for a negative pulse squares the input signal. 

3. Relaxation oscillator: A comparator can be used to build a relaxation oscillator. It uses both positive and negative feedback. The positive feedback is a Schmitt trigger configuration. Alone, the trigger is a bistable multivibrator. However, the slow negative feedback added to the trigger by the RC circuit causes the circuit to oscillate automatically. That is, the addition of the RC circuit turns the hysteretic bistable multivibrator into an astable multivibrator. 

4. Level shifter: This circuit requires only a single comparator with an open-drain output as in the LM393, TLV3011 or MAX9028. The circuit provides great flexibility in choosing the voltages to be translated by using a suitable pull up voltage. It also allows the translation of bipolar ±5 V logic to unipolar 3 V logic by using a comparator like the MAX972. 

5. Analog-to-digital converters: When a comparator performs the function of telling if an input voltage is above or below a given threshold, it is essentially performing a 1-bit quantization. This function is used in nearly all analog to digital converters (such as flash, pipeline, successive approximation, delta-sigma modulation, folding, interpolating, dual-slope and others) in combination with other devices to achieve a multi-bit quantization. 

6. Window detectors: Comparators can also be used as window detectors. In a window detector, a comparator used to compare two voltages and determine whether a given input voltage is under voltage or over voltage. 

Application of Zero Crossing Detector: 

1.It is particularly important in magnetic digital recordings. These are recorded as "transitions" from one polarity of magnetization to another, each transition representing a "bit". The location of these transitions is used to decode the recording. Since the transition goes from a positive value to a negative value (or vice versa) the zero crossing identifies the location of the transition. 

2.Zero crossing detectors are used in frequency counters. 

3.Zero crossing detectors are used in time interval meters. 

4.Another application is in electrical power control switching circuits. These circuits control power by interrupting the current flow for a number of AC cycles. Voltage spike and electrical noise are minimized if the switching occurs at the beginning or end of cycles, at the point where the voltage is momentarily zero. A zero-crossing detector controls the switching so that it occurs at close to zero voltage of the cycle.