INTRODUCTION TO ELECTRONICS
EHB 222E
Diodes II
Asst. Prof. Onur Ferhanoğlu
1
Rectifier Circuits
Building block of DC Power supplies
• Down-converts the voltage • Makes the signal unipolar
with an appropriate N1/N2 ratio
• Smoothens the output
• Provides isolation between
the equipment and the line
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
2
Half-wave rectifier
Using constant voltage drop model:
Useful for
vS >> vD
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
3
Full-wave rectifier
Utilizes both part of the sinusoid
Asst. Prof. Onur Ferhanoğlu
Diodes/ INTRODUCTION TO ELECTRONICS
• Transformer secondary
winding is center tapped
• When input is positive
both vs`s will be positive
D1 ON D2 OFF
• When input is negative
D2 OFF D1 ON
4
Bridge rectifier
• Requires 4 diodes
• Positive cycle:
D1, D2 ON
D3, D4 OFF
• Negative cycle:
D3, D4 ON
D1, D2 OFF
• 2VD drop from max value
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
5
Peak Rectifier
Output voltage should be constant in a DC power supply
• Using a filter capacitor reduces the variations in rectified voltage
• Assume diode is ideal
• As vI goes positive capacitor is charged vo = vI
• After the peak diode becomes reverse biased,
output value remains constant
(no way for the capacitor to be discharged)
Asst. Prof. Onur Ferhanoğlu
Diodes/ INTRODUCTION TO ELECTRONICS
6
Peak Rectifier
• There is always a resistance in a practical scenario
• Capacitor charges till peak
• After the peak, capacitor will discharge through the
resistor.
• Capacitor discharge continues till vI > vO
• C,R should be selected such that the time constant
is greater than the discharge interval (RC >> T)
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
7
Half vs. Full Peak Rectifier
Vr = Vp – Vpe-t/CR
Vr ~= Vp – Vp(1-T/CR)
= Vp/ fCR
Vr = Vp/ 2fCR
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
8
Limiter & clipper circuits
Limiter circuit provides an output that is proportional to the input
But limits the voltage above and below certain value
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
9
Limiter & clipper circuits
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
10
Limiter & clipper circuits
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
11
Limiter & clipper circuits
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
12
Limiter & clipper circuits
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
13
Limiter & clipper circuits
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
14
Limiter & clipper circuits
Exercise
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
15
Clamped Capacitor & DC restorter
If voltage is measured on the diode, as opposed to the capacitor:
• At negative cycle, diode is shorted. -> capacitor stores 6V (negative peak)
• At positive cycle, diode is open, v0 = vI + vC = 6 + 4 = 10 V
• Same peak to peak , DC restorted
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
16
Clamped Capacitor & DC restorter
DC restorter with resistor output
• In positive cycle, diode is OFF, capacitor, discharges through the resistor exponentially
• At t1, input decreases by Va and output follows this decrease
• Till t2 Capacitor is rapidly charged (diode is ON) to the low level of the input voltage
Asst. Prof. Onur Ferhanoğlu
Diodes / INTRODUCTION TO ELECTRONICS
17
Voltage Doubler
Clamped circuit (Diode 1) output
Peak rectifier output
CLAMPED CIRCUIT
Asst. Prof. Onur Ferhanoğlu
PEAK RECTIFIER
Diodes / INTRODUCTION TO ELECTRONICS
18