11.2.7 Investigating Diode Bridges

Investigating Diode Bridges

The aim of the experiment is experimentally verify a half-bridge rectifier will produce partial DC output from AC input and a full wave bridge rectifier will produce near complete DC output from AC input

Variables:

Half Wave Rectification

Experimental set-up for investigating half-wave rectification

Study the above circuit diagram carefully before setting up the appropriate circuit
Connect the single diode to the step-down transformer and resistor in circuit
Connect the resistor to the step-down transformer and the oscilloscope in parallel across the resistor
Before connecting and turning on the 220 V alternating current (AC) source, voltmeters and ammeters may be set up in appropriate locations to investigate points of interest such as across the diode or the output of the step-down transformer
- However, the oscilloscope is the most crucial measuring equipment for this experiment and is the only truly necessary measurement required for this practical if the circuit is set-up appropriately
Connect the step-down transformer to the 220 V AC source
Observe the oscilloscope and look at the voltage reading to confirm partial Direct Current (DC) output (half-wave rectification)

Full Wave Rectification

11-2-7-full-wave-rectification-diode-bridge-circuit-ib-hl

Experimental set-up for investigating full-wave rectification

Study the above circuit diagram carefully before setting up the appropriate circuit
Connect the components of the diode bridge ensuring that the necessary parallel and series diodes are connected so that they run alternatively during the opposite phases of alternating current
Connect the opposite edges of the diode bridge to the transformer making sure that there is an individual diode facing towards and one facing away from both junctions
Connect the capacitor and resistor in parallel with their outer connections to the points of the diode bridge where one point of the diode bridge has both diodes facing towards the junction and the opposite point where both of the diodes are facing away from the junction
Connect the oscilloscope in parallel across the resistor to measure the voltage across that component
Before connecting and turning on the 220 V AC source, voltmeters and ammeters may be set up in appropriate locations to investigate points of interest such as across the diode bridge, over the smoothing capacitor or the output of the step-down transformer
- However, the oscilloscope is the most crucial measuring equipment for this experiment and is the only truly necessary measurement required for this practical if the circuit is set-up appropriately
Connect the 220 V AC source to the step-down transformer
Observe the oscilloscope and look at the voltage reading to confirm DC output

The output of the oscilloscope for half-wave rectification should be similar to the following output:

11-2-7-half-wave-rectification-with-smoothing-ib-hl

The green line shows how the capacitor creates a smoothing effect that brings the output of the single diode closer to DC output

The output for the oscilloscope for full-wave rectification should be similar to the following output:

11-2-7-diode-bridge-with-smoothing-ib-hl

The green line shows how the capacitor creates a smoothing effect that brings the output of the diode bridge closer to DC output

Notice the smoothing effect which comes from the capacitor in the circuit and makes the output more like DC in nature

Systematic Errors:

The voltmeter and ammeters should start from zero, to avoid zero error in the readings

Random Errors:

In practice, the voltmeter and ammeter will still have some resistance, therefore the voltages and currents displayed may be slightly inaccurate
The temperature of the equipment could affect its resistance. This must be controlled carefully
Taking multiple readings of the current for each component will provide a more accurate result and reduce uncertainties

When there is a high current and a thin wire, the wire will become very hot
- Make sure never to touch the wire directly when the circuit is switched on
Switch off the power supply right away if burning is smelled
Make sure there are no liquids close to the equipment, as this could damage the electrical equipment
The components will get hot especially at higher voltages

In the case that an oscilloscope is not available, it may be possible to use a multimeter to check that the output is indeed similar to DC and able to be detected as such
- While the actual voltage pattern will not be visible, this would still allow the DC-like output to be verified and confirm that the diode bridge (full-wave rectification) does work experimentally
If access to a diode bridge and complete circuit is not possible, then there are often simulations available online which might allow the possibility to do this investigation virtually