Electronics; Rectifiers And Battery Chargers - B

Question 1

What is a rectifier?

Answer 1

Device that changes AC to DC

Question 2

What are the two main categories of rectifiers?

Answer 2

Half-wave

Full-wave

Question 3

What is the difference between a half-wave rectifier and a full-wave rectifier?

Answer 3

Half-wave = every second ac alternation is applied to the load

Full-wave = every ac alternation applied to the load

Question 4

What does a single phase half wave recifier consist of and how is it connected with respect to the load?

Answer 4

One diode. In series with the load.

Question 5

When is the diode of a single phase half wave recifier reverse-biased?

Answer 5

During the second alternation.

Question 6

When will a voltage appear across the load in a single phase half wave rectifier installation?

Answer 6

When the diode is forward biased and current is flowing.

Question 7

What is the voltage across the diode when it is reverse-biased? (Open switch)

Answer 7

Equal to the supply voltage

Question 8

What is the voltage across a forward-biased diode?

Answer 8

Near 0 (closed switch) equal to the barrier potential of the diode.

Question 9

What is the average voltage value (dc voltage value) of a single phase half wave recifier?

Answer 9

31.8% of the peak voltage. (1/pi)

Question 10

What kind of dc voltage is produced by a single-phase half wave recifier?

Answer 10

Pulsating DC

Question 11

What kind of frequency is produced by pulsating DC?

Answer 11

Ripple frequency

Question 12

What kind of rectification is provided by a centre-tapped transformer with two diodes?

Answer 12

Full-wave rectification

Question 13

How does the polarity of the load change as supply polarity changes, in a centre tapped full wave rectified circuit?

Answer 13

It does not change.

Question 14

What is the conversion factor for a single-phase full-wave rectifier?

Answer 14

0.637 of the peak value of the rectifier voltage

Question 15

What are the equations for V(dc) for:

1) single phase half wave
2) single phase full wave

Answer 15

1) V(dc) = V(peak) × (1/pi)

2) V(dc) = V(peak) × (2/pi)

Question 16

How do you determine centre-tapped secondary voltage given primary voltage and a transformer ratio?

Answer 16

(V(primary rms)/xfmer ratio)/2

Question 17

How do you find average load voltage for a load connected to a single-phase centre-tapped full-wave recified circuit?

Answer 17

V(dc) = (V(L1 or L2-N) ÷ 0.707) × (2/pi)

The product of ‘peak of the voltage applied to the load at any given time (half of secondary)’ and 2/pi

Question 18

What is the ripple frequency of the load voltage in a full-wave rectified circuit? Illustrate this using a waveform diagram.

Answer 18

Two times the supply frequency

Question 19

What is the most commonly used single-phase rectifier?

Answer 19

Single-phase full-wave bridge recifiers.

Question 20

How many diodes are used in a single-phase full-wave bridge rectifier?

Answer 20

4

Question 21

For a single phase full wave bridge rectifier, if current through the load is from C to D and is positive on the 1st alternation, what would the polarity be from C to D on the second alternation?

Answer 21

Also positive

Question 22

What is the first step in finding average load voltage?

Answer 22

Find V peak (of the voltage the load sees)

Question 23

How would you expect the result of V(dc) calculations to differ between single-phase full-wave bridge rectifier and single-phase centre-tapped full wave rectifier?

Answer 23

Bridge would be larger as Vpeak is based off full secondary voltage as opposed to half (centre-tapped) secondary voltage.

Question 24

What is the equation used to find average load voltage in a single-phase full-wave bridge rectifier circuit?

Answer 24

V(dc) = V(peak) × (2/pi)

Question 25

What is the ripple frequency of the load voltage in a single-phase full-wave bridge rectifier circuit?

Answer 25

2× supply frequency

Question 26

How is the source connected for a 3phase half wave recifier?

Answer 26

Wye connected

Question 27

How do you calculate the average voltage across the load connected to a half-wave three-phase rectifier?

Answer 27

V(dc avg) = V (peak of the phase) × 0.827

Question 28

What is the ripple frequency of the load voltage in a three phase half wave rectifier?

Answer 28

3 times the supply

Question 29

What is the average diode current in a three phase half wave recifier?

Answer 29

One-third the average load current. 1) I(load) = V(dc avg) / R (load) 2) I(diode) = I(load) / 3

Question 30

Which rectifier can be connected to either a wye or delta supply?

Answer 30

Three phase full wave rectifier. Neutral conductor not required.

Question 31

How do you find the average load voltage of a load connected to a three phase full wave rectifier?

Answer 31

1) V(peak of the line) = V(line) / 0.707 | 2) V(dc avg) = V(peak) × 0.955

Question 32

What is the ripple frequency of the load of a three phase full wave rectifier?

Answer 32

6 times the supply frequency.

Question 33

What is the basic construction of a three phase full wave rectifier module?

Answer 33

6 diodes, 5 leads (3ac input, 2 dc output), metallic back plate to be mounted to a heat sink

Question 34

What is a practical application of rectifiers?

Answer 34

Battery chargers

Question 35

How are battery chargers rated?

Answer 35

In current capacity

Question 36

What are the two main sections of a battery charger?

Answer 36

1) transformer with adjustable tap settings | 2) rectifier

Question 37

What do the voltage ratings on the primary of a battery charger transformer indicate?

Answer 37

Indicates the type of battery that the charger is connected to. NOT the actual voltage applied to the battery.

Question 38

What does changing the setting from low to high on the transformer of a battery charger do?

Answer 38

1) Increases the volts per turn ratio of the primary | 2) increases the voltage output of the secondary to the rectifier.

Question 39

What is the purpose of having two paralleled windings on the secondary of the transformer of a battery charger?

Answer 39

To reduce required secondary winding conductor size. (Provide increased current capacity at lower cost)

Question 40

What type of parallelled rectifiers are used in the battery charger displayed in the module?

Answer 40

Single phase full wave Center tapped

Question 41

What is each end of a secondary winding in a battery charger connected to?

Answer 41

On one end, solidly connected to for negative rail | On the other end, connected to the anodes of four press fit diodes

Question 42

Why do the parallelled diodes on the secondary of a transformer in a battery charger need to be a closely matched pair?

Answer 42

In order to prevent one diode handling more current than the other which would cause it to overheat

Question 43

What is the advantage of a double winding and diode arrangement for a battery charger?

Answer 43

Increase his reliability if one diode fails

Question 44

What are other components of battery chargers?

Answer 44

``` Overcurrent circuit breaker Ammeter Correct polarity indicator Charge time clock Power on indicator lamp ```

Question 45

Where are the three paralleled circuit breakers for a battery charger located?

Answer 45

Bolted to the heatsink

Question 46

How is the ammeter connected in a battery charger?

Answer 46

In series with the output

Question 47

How is a light emitting diode connected in order to indicate correct polarity of battery connection?

Answer 47

In series with a 220 Ohm resistor and connected across the output

Question 48

What component does the timer in a battery charger turn off?

Answer 48

The Transformer

Question 49

Where does the timer in a battery charger draw its power from?

Answer 49

Motor connected across AC input

Question 50

What internal connection does a power on indicator lab actually represent?

Answer 50

Connection between the ac input and the transformer, through the timer.

Question 51

How do you change the current setting on a battery charger?

Answer 51

By adjusting the voltage input to the rectifier by changing the tap on the primary of the Transformer with a selector switch

Question 52

Higher voltage to a battery charger causes (higher/lower) current to flow?

Answer 52

Higher

Question 53

What's the difference between a 12 volt low and 12 volt high setting on a battery charger?

Answer 53

The output voltage level. Low setting has a peak of 18 volts high setting has a peak of 20 volts

Question 54

What conditions are required in order for charging to actually happen?

Answer 54

charger voltage has to be higher than battery voltage

Question 55

What is applied to the load for half-wave recifiers?

Answer 55

Every second alternation

Question 56

What is applied to the load for full wave rectifiers?

Answer 56

Every ac alternation

Question 57

When does voltage appear across the load in a single-phase half wave recifier?

Answer 57

When the recifier is forward biased

Question 58

What percentage of peak voltage is the average voltage value of the output of a single phase half wave recifier?

Answer 58

31.8%

Question 59

Where would a single phase half wave recifier leads be connected for power?

Answer 59

L1 and N Or L2 and N

Question 60

What is the ripple frequency of a single phase half wave recifier?

Answer 60

Equal to supply frequency