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4th Year Electrical > Electronics; Rectifiers And Battery Chargers - B > Flashcards

Electronics; Rectifiers And Battery Chargers - B Flashcards

1
Q

What is a rectifier?

A

Device that changes AC to DC

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2
Q

What are the two main categories of rectifiers?

A

Half-wave

Full-wave

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3
Q

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

A

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

Full-wave = every ac alternation applied to the load

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4
Q

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

A

One diode. In series with the load.

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5
Q

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

A

During the second alternation.

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6
Q

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

A

When the diode is forward biased and current is flowing.

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7
Q

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

A

Equal to the supply voltage

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8
Q

What is the voltage across a forward-biased diode?

A

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

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9
Q

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

A

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

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10
Q

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

A

Pulsating DC

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11
Q

What kind of frequency is produced by pulsating DC?

A

Ripple frequency

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12
Q

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

A

Full-wave rectification

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13
Q

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

A

It does not change.

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14
Q

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

A

0.637 of the peak value of the rectifier voltage

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15
Q

What are the equations for V(dc) for:

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

A

1) V(dc) = V(peak) × (1/pi)

2) V(dc) = V(peak) × (2/pi)

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16
Q

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

A

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

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17
Q

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

A

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

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18
Q

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

A

Two times the supply frequency

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19
Q

What is the most commonly used single-phase rectifier?

A

Single-phase full-wave bridge recifiers.

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20
Q

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

A

4

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21
Q

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?

A

Also positive

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22
Q

What is the first step in finding average load voltage?

A

Find V peak (of the voltage the load sees)

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23
Q

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?

A

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

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24
Q

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

A

V(dc) = V(peak) × (2/pi)

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25
Q

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

A

2× supply frequency

26
Q

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

A

Wye connected

27
Q

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

A

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

28
Q

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

A

3 times the supply

29
Q

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

A

One-third the average load current.

1) I(load) = V(dc avg) / R (load)
2) I(diode) = I(load) / 3

30
Q

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

A

Three phase full wave rectifier. Neutral conductor not required.

31
Q

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

A

1) V(peak of the line) = V(line) / 0.707

2) V(dc avg) = V(peak) × 0.955

32
Q

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

A

6 times the supply frequency.

33
Q

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

A

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

34
Q

What is a practical application of rectifiers?

A

Battery chargers

35
Q

How are battery chargers rated?

A

In current capacity

36
Q

What are the two main sections of a battery charger?

A

1) transformer with adjustable tap settings

2) rectifier

37
Q

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

A

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

38
Q

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

A

1) Increases the volts per turn ratio of the primary

2) increases the voltage output of the secondary to the rectifier.

39
Q

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

A

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

40
Q

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

A

Single phase full wave Center tapped

41
Q

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

A

On one end, solidly connected to for negative rail

On the other end, connected to the anodes of four press fit diodes

42
Q

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

A

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

43
Q

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

A

Increase his reliability if one diode fails

44
Q

What are other components of battery chargers?

A 
Overcurrent circuit breaker
Ammeter
Correct polarity indicator
Charge time clock
Power on indicator lamp
45
Q

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

A

Bolted to the heatsink

46
Q

How is the ammeter connected in a battery charger?

A

In series with the output

47
Q

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

A

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

48
Q

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

A

The Transformer

49
Q

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

A

Motor connected across AC input

50
Q

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

A

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

51
Q

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

A

By adjusting the voltage input to the rectifier by

changing the tap on the primary of the Transformer with

a selector switch

52
Q

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

A

Higher

53
Q

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

A

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

54
Q

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

A

charger voltage has to be higher than battery voltage

55
Q

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

A

Every second alternation

56
Q

What is applied to the load for full wave rectifiers?

A

Every ac alternation

57
Q

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

A

When the recifier is forward biased

58
Q

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

A

31.8%

59
Q

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

A

L1 and N
Or
L2 and N

60
Q

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

A

Equal to supply frequency

4th Year Electrical (24 decks)

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