Circuit Configuration (Figure a)
Grounded center tap on secondary winding
Equivalent to two half-wave rectifiers
Each rectifier receives half the secondary voltage
Operation
Diode D1: Conducts on positive half-cycle
Diode D2: Conducts on negative half-cycle
Rectified load current flows during both half-cycles
Positive Half-Cycle (Figure b)
D1 is forward biased
Positive load voltage across load resistor
Negative Half-Cycle (Figure c)
D2 is forward biased
Positive load voltage
Output Characteristics
Same load voltage polarity during both half-cycles
Load current direction remains constant
Converts AC input to pulsating DC output (Figure d)
DC or Average Value
Full-wave rectifier average value: \[V_{\mathrm{dc}} = \frac{2 V_p}{\pi}\]
Approximate form: \[V_{\mathrm{dc}} \approx 0.636 V_p\]
Example:
Peak voltage, \(V_p = 100\text{ V}\)
DC voltage: \(V_{\mathrm{dc}} \approx 63.6\text{ V}\)
Output Frequency
Half-wave rectifier: Output frequency = Input frequency
Full-wave rectifier: Output frequency is double the input frequency
Input frequency: \(f_{\text{in}} = 60\text{ Hz}\)
Input period: \[T_{\text{in}} = \frac{1}{f_{\text{in}}} = \frac{1}{60\text{ Hz}} = 16.7\text{ ms}\]
Output period: \[T_{\text{out}} = 0.5 \times T_{\text{in}} = 8.33\text{ ms}\]
Output frequency: \[f_{\text{out}} = \frac{1}{T_{\text{out}}} = 120\text{ Hz}\]
General relation: \[f_{\text{out}} = 2 f_{\text{in}}\]
Second Approximation
Full-wave rectifier \(\approx\) Two back-to-back half-wave rectifiers
Approximate peak output voltage: \[V_{\text{peak,approx}} = V_p - 0.7\text{ V}\]
Example to illustrate the idea.
LAB example of full-wave rectifier
\[\begin{aligned} V_m & = \sqrt{2} \cdot V_{rms} = \sqrt{2} \times 120 = 170 \mathrm{~V} \\ V_{p(2)} &=\frac{V_{p(1)}}{N_1 / N_2}=\frac{170 \mathrm{~V}}{10}=17 \mathrm{~V}\\ V_{p(\mathrm{in})} & =0.5(17 \mathrm{~V})=8.5 \mathrm{~V} \\ V_{p(\text { out })} & =8.5 \mathrm{~V}\\ V_{p(\text { out })} & =8.5 \mathrm{~V}-0.7 \mathrm{~V}=7.8 \mathrm{~V} \end{aligned}\]
Bridge Rectifier
Bridge Rectifier Circuit
Produces a full-wave output voltage
Diodes D1 and D2 conduct on positive half-cycle
Diodes D3 and D4 conduct on negative half-cycle
Rectified load current flows during both half-cycles
Positive Half-Cycle
D1 and D2 are forward biased
Produces positive load voltage
Visualize D2 shorted: Circuit resembles half-wave rectifier
Negative Half-Cycle
D3 and D4 are forward biased
Produces positive load voltage
Visualize D3 shorted: Circuit resembles half-wave rectifier
Output Characteristics
Same load voltage polarity during both half-cycles
Load current direction remains constant
Converts AC input to pulsating DC output
Advantage: Uses entire secondary voltage
Average Value: \[V_{\mathrm{dc}} = \frac{2 V_p}{\pi}\]
63.6% of peak value
Example: \(V_{\mathrm{dc}} = 63.6\text{ V}\) for \(V_p = 100\text{ V}\)
Output Frequency: \[f_{\mathrm{out}} = 2 f_{\mathrm{in}}\]
Example: \(f_{\mathrm{out}} = 120\text{ Hz}\) for \(f_{\mathrm{in}} = 60\text{ Hz}\)
Advantage:
Uses entire secondary voltage
Twice as much peak voltage and DC voltage compared to center-tap full-wave rectifier
Terminology:
Full-wave rectifier may refer to:
Conventional full-wave rectifier
Two-diode full-wave rectifier
Center-tapped full-wave rectifier
Peak Output Voltage: \[V_{p(\text{out})} = V_{p(\text{in})} - 1.4\text{ V}\]
Subtract 1.4 V (two diode drops) for accurate peak load voltage
Summary Table:
