asst. prof. onur ferhanoğlu · asst. prof. onur ferhanoğlu diodes / introduction to electronics...

INTRODUCTION TO ELECTRONICS

EHB 222E

Diodes II

Asst. Prof. Onur Ferhanoğlu

1

Rectifier Circuits

2Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Building block of DC Power supplies

• Down-converts the voltagewith an appropriate N1/N2 ratio• Provides isolation between

the equipment and the line

• Makes the signal unipolar

• Smoothens the output

Half-wave rectifier

3Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Using constant voltage drop model:

Useful forvS >> vD

Full-wave rectifier

4Asst. Prof. Onur Ferhanoğlu Diodes/ INTRODUCTION TO ELECTRONICS

Utilizes both part of the sinusoid• Transformer secondary

winding is center tapped• When input is positive

both vs`s will be positiveD1 ON D2 OFF

• When input is negativeD2 OFF D1 ON

Bridge rectifier

5Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

• Requires 4 diodes• Positive cycle:

D1, D2 OND3, D4 OFF

• Negative cycle:D3, D4 OND1, D2 OFF

• 2VD drop from max value

Peak Rectifier

6Asst. Prof. Onur Ferhanoğlu Diodes/ INTRODUCTION TO ELECTRONICS

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)

Peak Rectifier

7Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

• 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)

Half vs. Full Peak Rectifier

8Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Vr = Vp – Vpe-t/CR

Vr ~= Vp – Vp(1-T/CR)= Vp/ fCR

Vr = Vp/ 2fCR

Limiter & clipper circuits

9Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter circuit provides an output that is proportional to the inputBut limits the voltage above and below certain value

Limiter & clipper circuits

10Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter & clipper circuits

11Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter & clipper circuits

12Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter & clipper circuits

13Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter & clipper circuits

14Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Limiter & clipper circuits

15Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

Exercise

Clamped Capacitor & DC restorter

16Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

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

Clamped Capacitor & DC restorter

17Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

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

Voltage Doubler

18Asst. Prof. Onur Ferhanoğlu Diodes / INTRODUCTION TO ELECTRONICS

CLAMPED CIRCUIT PEAK RECTIFIER

Clamped circuit (Diode 1) output

Peak rectifier output