Basic Elec. Engr Basic Elec. Engr. Lab . Lab ECS 204 ECS 204 - PowerPoint PPT Presentation

Basic Elec. Engr Basic Elec. Engr. Lab . Lab ECS 204 ECS 204 Asst. Prof. Dr. Prapun Suksompong prapun@siit.tu.ac.th Diode • Transformer • Lab 6 Rectifiers • Electrolytic Capacitor • 1

Diode 2

Unidirectional current characteristics  Permit current to flow through in one direction (when forward-biased ), but not the other ( reverse-biased ). 3

Transformer 4

Transformer 240 V 5

Part A: Half-Wave Rectifier (HWR) � �� � � � � � 240 V  A rectifier is an electrical device that converts alternating current (AC) to direct current (DC). 7

Part A: Half-Wave Rectifier (HWR) � �� � � � � � = � ��� � � ��� � � � ��� � 8

Use the osc. in DC mode Wrong 9

Part A: Half-Wave Rectifier (HWR) � �� � � � � � = � ��� � � ��� � � � ��� � 10

Part A: Full-Wave Rectifier (FWR) D1 1N4001 T1 S1 A + 240 V v in D B 220 V - D2 + 50 Hz v in 1N4001 + C - R L V out S2 10 k  _ 11

Part A: Full-Wave Rectifier (FWR) � �� � � � � � = � ��� � � ��� � � � ��� � 12

Part B: Filter Capacitor D1 T1 A 1N4001 240 V B D 240 V D2 50 Hz + + C1 C 1N4001 R1 100  F V out 10k  50 V _ _ ripple waveform 13

Electrolytic Capacitor  The polarity is almost always indicated by a printed band.  The lead nearest to that band is the cathode lead (-).  Additionally, the positive lead is usually longer.  Hook them up the wrong way and at best, you’ll block the signal passing through. At worst (for higher voltage applications) they’ll explode. Also check that it is 100-  F 50-V 15

Oscilloscope: DC mode vs. AC mode    Input signal: v t      DC mode: Show  v t v t DC      AC mode: Show   V v t v t DC AC  v AC ( t ) always have 0 average (theoretically)      when V DC = 0.  v t v t AC DC 16

Not enough to move the interesting part of the DC vs. AC waveform into the screen In DC mode… In AC mode… 17

Part B: Filter Capacitor + Load D1 T1 A 1N4001 240 V B D 240 V D2 50 Hz + + C1 C 1N4001 R L R1 100  F V out 1k  10k  50 V _ _ 19

Summary: Rectifiers  Use diode to rectify AC waveform  Use large capacitor to reduce ripple  Two dangerous mistakes:  Unknowingly shorting between nodes (A, B, C) of the transformer outputs D1 1N4001 T1 S1 A  You will smell something + v in D B 220 V burning. - D2 + 50 Hz v in 1N4001 + C - R L V out  Reverse the polarity of S2 10 k  _ the capacitor 21

Part C: Bridge rectifier 22

For next quiz … Op-Amp 741  OP erational AMP lifier V+ , Positive (Not connected) power supply Noninverting (1) Offset null NC (8) (7) input (2) Inverting (3) V+ (7) (6) input (3) Noninverting + Output (6) (2) Output input (4) Inverting (4) V- Offset null (5) V- , Negative input power supply 23