These two circuits contain two diodes instead of 1 diode as before. The first circuit has two voltage sources each 180 deg out of phase, while the other only has one voltage source. 

For Circuit 1 (2 voltage sources), the top diode only conducts current during for a short time within the positive half cycle of the voltage u1. When u1 goes negative the voltage source u2 now goes positive and the vertical diode can now conduct current. The output voltage in this case has a maximum value that is the same as the peak value of the input voltage. This circuit is essentially two half bridge circuits being joined to a common output capacitor and load. 

Circuit 2 also has two diodes but in this case only one voltage source. The two diodes now allow current to flow to the load during both the positive and negative half cycles of the voltage source. Since the voltage source is connected to the centre point between the two capacitors this circuit now produces an output voltage that is twice the voltage expected by a single half bridge rectifier. This circuit is also known as a “voltage doubler”. On the positive half cycle current flows through the top diode when the source voltage exceeds the voltage on C1. Notice how the current flows into C1 (charging it up) and the load, with its return path coming back through C2 (causing it discharge). On the negative voltage cycle, the current flows in C2 (charging it up) and through C1 (discharging it) and then through the load. The combined current then flows back through bottom diode to the voltage source. Notice that for the same output power level that the load resistor value has to be four times larger.

• In both circuits the time position on the waveform can be moved to see how the current path changes for each circuit.
• For circuits 1 and 2: Change the output load resistor value to see how the diode current and the ripple on the output changes.
• In Circuit 2 notice how the voltage level on the output is now different to Circuit 1.