Brighton Webs Ltd.
Statistics for Energy and the Environment
One of the functions of a diode is to prevent the flow of current in one direction. An example of this type of application is to protect a solar panel connected to a battery. When the emf generated by the solar panel is greater than that created by the battery, there is a flow of current into the battery. However, at night, the emf created by the panel drops to zero whilst that of the battery is greater than zero. Without a blocking diode, the battery would try and pass current through the PV panels.
Whilst experimenting with a small 12 volt PV system, it became apparent that the choice of components to perform this blocking function, could influence system efficiency. The first attempt was used a standard silicon rectifer diode, the voltage drop accross this component was aound 0.75 volts. In a 12 volt system this represents a loss of around 6%. This is a relatively small amount, but to accept it, might require specifying a larger PV panel, thus there some economic incentive to minimize losses. The next step was to use a Schottky diode, this reduced the voltage drop to around 0.25 volts for a small increase in cost.
The system has a high voltage disconnect to prevent the battery over charging. This is based on a MOSFET. A comparator keeps the gate voltage high as long as the voltage across the battery is less than 13.5 volts. A MOSFET is an efficient switching device, the component we are using has a drain/sink voltage drop of arount 0.05 volts at for a current of 1.0 amps. This loss is insignificant, thus working out a way to make the MOSFET act as a blocking device is an attractive line of development.
The graph below shows the voltage drop across the tested devices plotted against the current through them:
