Comparator and Zero Crossing Detectors (ZCD) is all too familiar circuit required in power electronics for control applications. This control can be to turn ON a Thyristor. For example, it is desired to set the output of a circuit TRUE (ON State) whenever a control signal is issued. This control signal is issued by setting either a variable DCvoltage or a variable amplitude pulse generator. This amplitude will be used as a signal to change the output state. This signal is called as ZCD. In any case the amplitude of control signal can not be greater than analog signal itself. Suppose it is required to set the output to TRUE state whenever the control signal crosses say+10V, then the second input of the operational amplifier is used to set to trigger at +10V. In other words, this second signal becomes a control voltage required to perform ZCD. This trainer consists of a monolithic FET input operational amplifier, which compares the actual signal, and ZCD operation is performed. In order to perform this experiment a ZCD with a two way switch is used. In one position an internal variable DC signal can be connected, in other position an external variable amplitude pulse generator can be connected. For Analog signal terminal an external function generator can be connected. You can observe input, ZCD and output waveforms on a CRO. This trainer requires an additional Lab power supply of 12V @ 500mA. |
