Mutchus

In most cases where you want to control an AC load, a triac or SCRs will be used. However, it is not easy to drive a triac or SCR. The drive requirement for the triac or SCR makes it sometimes difficult to control it as we want. One thing is that we can not turn the triac or SCR on or off as we desire, because once we turn it on, it latches and stays on until the next zero crossing or until current stops flowing through it. Also, driving a triac with reference to MT1 (or A1) is not as straightforward as we would want. However, a MOSFET can be controlled as we want. Set the gate high (with a sufficient voltage) and current can flow from drain to source. Set the gate low and current can no longer flow. Convenient! However, a MOSFET can only be used to control DC loads since it is a unidirectional switch - current flow can be controlled when it is flowing from drain to source, but can not be controlled from source to drain. So, certainly it can not be used to control AC loads. Right? Well...

Single Ended Class A power Amplifier with Resistor load The below fig shows a simple series-fed class A amplifier with resistive load R C . The transistor used here is under fixed biasing condition. As the input signal is applied, the transistor operates in active-region and hence the amplified power output appears across the load resistor. The static output characteristics along with input, output waveforms are shown in the below Pic 2.                                                                    Pic 1  Series Fed Class A Amplifier                                                     Pic 2 Input and Output Characteristics of a Series Fed Amplifier For the purpose of analysis, we as...