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

• Asst. Prof. Dr. Prapun Suksompong

prapun@siit.tu.ac.th

1

Basic Elec. Engr Basic Elec. Engr. Lab . Lab

ECS 204 ECS 204

Lab 6

• Diode
• Transformer
• Rectifiers
• Electrolytic Capacitor

Diode

2

Unidirectional current characteristics

3

 Permit current to flow through in one direction (when

forward-biased), but not the other (reverse-biased).

Transformer

4

Transformer

5

240 V

Part A: Half-Wave Rectifier (HWR)

7

 A rectifier is an electrical device that converts alternating

current (AC) to direct current (DC).

240 V

Part A: Half-Wave Rectifier (HWR)

8

=

Use the osc. in DC mode

9

Wrong

Part A: Half-Wave Rectifier (HWR)

10

=

Part A: Full-Wave Rectifier (FWR)

11

T1 220 V 50 Hz A B C D + _ Vout D1 1N4001 D2 1N4001 RL 10 k S1

+ vin

• +

vin

• S2

240 V

Part A: Full-Wave Rectifier (FWR)

12

=

T1 240 V 50 Hz + _ Vout D1 1N4001 D2 1N4001 A B C R1 10k C1 100 F 50 V + _ D

Part B: Filter Capacitor

13

240 V

ripple waveform

Electrolytic Capacitor

15

 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

Oscilloscope: DC mode vs. AC mode

16

 Input signal:  DC mode: Show  AC mode: Show

 vAC(t) always have 0 average (theoretically)



when VDC = 0.

 

v t

   

DC

V

AC

v t v t  

   

DC

v t v t 

   

AC DC

v t v t 

DC vs. AC

17

In AC mode…

Not enough to move the interesting part of the waveform into the screen

In DC mode…

T1 240 V 50 Hz + _ Vout RL 1k D1 1N4001 D2 1N4001 A B C R1 10k C1 100 F 50 V + _ D

Part B: Filter Capacitor + Load

19

240 V

Summary: Rectifiers

21

 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

 You will smell something

burning.  Reverse the polarity of

the capacitor

T1 220 V 50 Hz A B C D + _ Vout D1 1N4001 D2 1N4001 RL 10 k S1

• +

• S2

Part C: Bridge rectifier

22

For next quiz … Op-Amp 741

23

 OPerational AMPlifier

(1) Offset null + (2) Inverting input (3) Noninverting input (4) V- NC (8) V+ (7) Offset null (5) Output (6) Noninverting input Inverting input V+ , Positive power supply V- , Negative power supply Output (3) (2) (7) (4) (6)

(Not connected)