Full Wave Rectification
The diodes take turns conducting the current along the circuit.
This is a centre tapped transformer. It has an additional wire connected to the centre of the secondary winding. This divides input voltage into two equal and opposite voltages.
The DC waveform is made up of positive and negative cycles following one after the other.
Test it out
Tap the diagram for more information and click on the buttons to change a component and see what happens!
Show Positive Cycle
Show Negative Cycle
Add Smoothing Capacitor
Full Wave Bridge
Example calculations
In order to work with Full Wave Rectification, electrical engineers need to understand and work with a variety of calculations. Here are just a few:
Capacitor Size Calculation:
C=VM×TVRIPPLE×RLC = \frac{VM \times T}{V_{RIPPLE} \times RL}
Voltage Drop due to diode conduction:
VDROP=0.6×2V_{DROP} = 0.6 \times 2
Transformer output voltage:
T.R.=V2V1=N2N1T.R. = \frac{V2}{V1} = \frac{N2}{N1}
Centre Tapped TransformerT1T_1
Load ResistanceRL1RL_1
Smoothing CapacitorCC
When using a half wave rectifier, a large amount of power gets wasted as only one half of the AC wave passes through. Full wave rectification converts both sides of the alternating current (AC) wave into a more stable and efficient direct current (DC). Using both halves of the AC wave increases the output voltage significantly.
A full wave rectifier consists of two diodes connected to a single load resistance. Each diode takes a turn to supply current to the load. The centre tapped transformer is responsible for splitting the primary current into two equal halves.
During the positive half cycle, the top of the secondary winding in the transformer becomes positively charged, whilst the bottom becomes negatively charged. This causes diode D1 to become forward biased, allowing the current to flow through it, whilst diode D2 becomes reverse biased, blocking the current. This allows the positive wave to flow through.
During the negative half cycle, the top of the secondary winding becomes negative, and the bottom becomes positive, causing diode D1 to become reverse biased and diode D2 to become forward biased. This allows the negative wave to flow through.
The result is a DC waveform that is made up of both the positive and negative halves of the wave following on from each other.
Practice Questions
Test your new knowledge on full-wave rectification by answering these questions.
1. If you increase the size of the load resistance, how will this affect the size of the smoothing capacitor?
2. What is the relationship between the smoothing capacitor and supply frequency?
3. What is the effect of adding a smoothing capacitor in parallel to the load resistance for a full wave rectification circuit?