Half-wave Rectifiers
Half-wave rectifiers
– A rectifier converts AC voltage into DC voltage.
– Rectifiers are found in all power supplies that operate from an ac voltage source.
a) Basic power supply
– Converts standard 110 Vac into constant dc voltage.
– All electronic devices (TVs, VCRs, DVDs, etc) have one.
– A rectifier converts the ac input voltage to a pulsating dc voltage.
– The filter eliminates the fluctuations in the rectified voltage.
– The regulator maintains a constant dc voltage for different inputs and loads.
– The load is the circuit (or device) receiving power from the source.
Figure: Block diagram of a rectifier and a dc power supply with a load.
a) Half-wave rectifier
- The process of half-wave rectification is illustrated below.
Figure: Operation of a half-wave rectifier.
– When sinusoidal input (Vin) goes positive, diode is forward biased, thus conducts current.
– The output voltage keeps the shape of the input voltage.
– When Vin becomes netagive (second half of cycle), diode is reverse biased.
– There is no current.
– Thus, voltage across resistor RL is 0V.
– Net result is a pulsating dc voltage with same frequency as input.
– Average value of pulsating wave is
VAVG = Vp/p
– Note that we also have to take the 0.7 V from the barrier potential into account. Thus we sould get:
Vp(out) = Vp(in) – 0.7 V
a) Peak Inverse Voltage (PIV)
– PIV equals the peak value of the input voltage.
– Diode MUST be able to withstand this amount of repetitive reverse voltage.
PIV = Vp(in)
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