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


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


• 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


• 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


Vr = Vp – Vpe-t/CR

Vr ~= Vp – Vp(1-T/CR)= Vp/ fCR

Vr = Vp/ 2fCR

Limiter & clipper circuits


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



Exercise

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

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

Voltage Doubler


CLAMPED CIRCUIT PEAK RECTIFIER

Clamped circuit (Diode 1) output

Peak rectifier output

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

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