Lecture 6- Simple Diode Rectifier and Full Wave Rectifier

What are a rectifier purpose?

(1) to convert the mains voltage AC source to a lower voltage DC output and (2) to regulate the DC voltage and protect the device from fluctuations in the AC grid voltage.

Rectifier

A power converter is called a rectifier when it converts AC voltage/current/power to DC. By contrast, a converter is called an inverter when it converts DC to AC.

controllable converter

A power converter that uses a controllable semi-conductor switch is a controllable converter;

uncontrollable converter

an uncontrollable converter is one that does not use a controllable switch (a passive device).

Diode

: An uncontrollable switch or device which turns on when a voltage is applied in a particular direction and turns off when the applied voltage is zero or negative.

Thyristor:

A semi-controllable switch or device which turns on when a control signal is applied but only turns off when the voltage applied to the device is zero or negative.

Transistor:

A controllable switch or device which is switched on and off by a control signal.

A simple diode rectifier

The diode is a unidirectional switch so only conducts when the device is positively biased, meaning it has a relatively positive voltage applied to its anode compared to the cathode. When positively biased, the ideal diode acts as a short circuit (with zero resistance) and applies the source voltage 𝑣𝑠 to the load and conducts current

Limitations of half-wave rectifier

The half-wave rectifier provides a simple means of converting AC to DC but it has its limitations

• By only rectifying half the source voltage, the output does not make maximum use of the source.

• The output voltage has a period of zero output and no load current. This leads to problems such as flicker in LED lighting. The light has on/off periods during the 50 Hz electrical cycle and the human eye can detect this.

• The converter is passive such that the source voltage determines the output. There is no output control.

Diodes in full wave diode rectifier

Positive source: 𝐷1 and 𝐷4are positively biased.

Negative source: 𝐷2 and 𝐷3are positively biased.