The previous example used a couple of diodes, and a capacitor between the center tap and the top diode to rectify and smooth the output voltage wave form, as shown in the center tapped topology above. It is worth noting that other topologies can be used for the secondary side. Other topologies include a diode bridge which provides full wave rectification. A diode bridge is more efficient use of the transformer, but at the expense of two additional diodes. Voltage doubler topologies are useful when creating voltages significantly higher than the input voltage. Doubler topologies can also be combined to produce tracking outputs commonly found in industrial applications.