| The half-wave diode rectifier circuit is one of the simplest power electronic circuits to construct since it uses a two terminal power device, called the diode. The diode is an uncontrolled device that will conduct current in only one direction when the correct biasing conditions are applied to it. One typical application for a diode is to convert AC into DC. The simplest circuit is called the “half-wave” rectifier and is constructed using only 1 diode connected to an AC supply. As its name implies it only works for one half of the sine voltage waveform. During the negative half of the supply voltage the diode is blocking current and is acting like an open circuit. This is shown in the diode characteristic graphic where the current iD is zero when the voltage uD is negative. When there is a positive voltage across the diode it is conducting current. The diode has an i-v characteristic that has an exponential form in its conducting state. By adjusting the voltage applied you can see the operating point of the diode on the diode characteristic. When the circuit is operated from a mains voltage supply then the voltage drop across the diode, a maximum of 1.6V in this case, is insignificant compared to the supply voltage and the diode can be treated as an ideal component. However when the supply voltage is reduced to 10V peak then the diode voltage drop is significant and must be taken into account. This is the case for a mobile phone charger where a small 50Hz transformer reduces the mains voltage to a low level before the rectifier. For the low voltage level case as the time bar is the change in the voltage across the diode can be seen. The diode voltage drop uD is significant and has reduced the amount of voltage available for the load. In this example, a purely resistive load has been used. In practice this is not the only type of load that will be connected to a half wave rectifier. In the other applets inductive-resistive loads are also given. |
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