# Práctica 7.docx - INSTITUTO POLITÉCNICO NACIONAL ESCUELA...

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ANALOGUE ELECTRONICS PRACTICE REPORT 7: LEVEL COMPARATORS AND APPLICATIONS. PROFESSOR: ISMAEL CERVANTES DE ANDA. MEMBERS: CORTEZ TINOCO ALEJANDRO. FONSECA MIRA DANIEL ESTEBAN. RAMOS RAMÍREZ ANTONIO. OBJECTIVE: Check the use of the comparators simples and with hysteresis. Make with the simple comparators some applications. Make with the hysteresis comparators some applications. Interpret results obtained. INSTITUTO POLITÉCNICO NACIONAL ESCUELA SUPERIOR DE CÓMPUTO

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INTRODUCTION. HYSTERESIS. In electricity, the hysteresis loop occurs when a metal is subjected to a varying magnetic field. Once you remove the metal from the magnetic field it is still loaded, so the act of made a charge and discharge cycle produces losses. Making a zero crossing detector circuit is actually very easy and it could be effectively applied for protecting sensitive electronic equipment against mains switch ON surges. A zero crossing detector circuit is mainly used for protecting electronic devices from switch ON surges by ensuring that during power switch ON the mains phase always "enters' the circuit at its first zero crossing point. So what is a zero crossing detector? We all know that our mains AC phase is made up of alternating sinusoidal voltage phases as shown below: In this alternating AC, the current can be seen alternating across the central zero line and across the top positive and bottom negative peak levels, through a particular phase angle. This phase angle can be seen rising and declining exponentially, meaning it is doing so in a gradually rising and gradually falling manner . The alternating cycle in an AC happens 50 times per second for 220V mains and 60 times per second for 120V mains inputs as set by the standard rules. This 50 cycle response is called 50 Hz frequency and the 60 Hz is called 60 Hz frequency for these mains outlets in our homes. Whenever we switch ON an appliance or an electronic device to the mains, it is subjected to a sudden entry of the AC phase, and if this entry
point happens to be at the peak of the phase angle could imply maximum current being forced to the device at the switch ON point. Although, most devices will be ready for this and might be equipped with protection stages using resistors, or NTC or MOV, it is never recommended to subject them to such sudden unpredictable situations. To tackle such an issue, a zero crossing detector stage is used which ensures that whenever a gadget is switched ON with mains power, the zero crossing circuit waits until the AC phase cycle reaches the zero line, and at this point it switches ON the mains power to the gadget.

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