Electronics; Rectifiers And Battery Chargers - B Flashcards
What is a rectifier?
Device that changes AC to DC
What are the two main categories of rectifiers?
Half-wave
Full-wave
What is the difference between a half-wave rectifier and a full-wave rectifier?
Half-wave = every second ac alternation is applied to the load
Full-wave = every ac alternation applied to the load
What does a single phase half wave recifier consist of and how is it connected with respect to the load?
One diode. In series with the load.
When is the diode of a single phase half wave recifier reverse-biased?
During the second alternation.
When will a voltage appear across the load in a single phase half wave rectifier installation?
When the diode is forward biased and current is flowing.
What is the voltage across the diode when it is reverse-biased? (Open switch)
Equal to the supply voltage
What is the voltage across a forward-biased diode?
Near 0 (closed switch) equal to the barrier potential of the diode.
What is the average voltage value (dc voltage value) of a single phase half wave recifier?
31.8% of the peak voltage. (1/pi)
What kind of dc voltage is produced by a single-phase half wave recifier?
Pulsating DC
What kind of frequency is produced by pulsating DC?
Ripple frequency
What kind of rectification is provided by a centre-tapped transformer with two diodes?
Full-wave rectification
How does the polarity of the load change as supply polarity changes, in a centre tapped full wave rectified circuit?
It does not change.
What is the conversion factor for a single-phase full-wave rectifier?
0.637 of the peak value of the rectifier voltage
What are the equations for V(dc) for:
1) single phase half wave
2) single phase full wave
1) V(dc) = V(peak) × (1/pi)
2) V(dc) = V(peak) × (2/pi)
How do you determine centre-tapped secondary voltage given primary voltage and a transformer ratio?
(V(primary rms)/xfmer ratio)/2
How do you find average load voltage for a load connected to a single-phase centre-tapped full-wave recified circuit?
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
What is the ripple frequency of the load voltage in a full-wave rectified circuit? Illustrate this using a waveform diagram.
Two times the supply frequency
What is the most commonly used single-phase rectifier?
Single-phase full-wave bridge recifiers.
How many diodes are used in a single-phase full-wave bridge rectifier?
4
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?
Also positive
What is the first step in finding average load voltage?
Find V peak (of the voltage the load sees)
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?
Bridge would be larger as Vpeak is based off full secondary voltage as opposed to half (centre-tapped) secondary voltage.
What is the equation used to find average load voltage in a single-phase full-wave bridge rectifier circuit?
V(dc) = V(peak) × (2/pi)
What is the ripple frequency of the load voltage in a single-phase full-wave bridge rectifier circuit?
2× supply frequency
How is the source connected for a 3phase half wave recifier?
Wye connected
How do you calculate the average voltage across the load connected to a half-wave three-phase rectifier?
V(dc avg) = V (peak of the phase) × 0.827
What is the ripple frequency of the load voltage in a three phase half wave rectifier?
3 times the supply
What is the average diode current in a three phase half wave recifier?
One-third the average load current.
1) I(load) = V(dc avg) / R (load)
2) I(diode) = I(load) / 3
Which rectifier can be connected to either a wye or delta supply?
Three phase full wave rectifier. Neutral conductor not required.
How do you find the average load voltage of a load connected to a three phase full wave rectifier?
1) V(peak of the line) = V(line) / 0.707
2) V(dc avg) = V(peak) × 0.955
What is the ripple frequency of the load of a three phase full wave rectifier?
6 times the supply frequency.
What is the basic construction of a three phase full wave rectifier module?
6 diodes, 5 leads (3ac input, 2 dc output), metallic back plate to be mounted to a heat sink
What is a practical application of rectifiers?
Battery chargers
How are battery chargers rated?
In current capacity
What are the two main sections of a battery charger?
1) transformer with adjustable tap settings
2) rectifier
What do the voltage ratings on the primary of a battery charger transformer indicate?
Indicates the type of battery that the charger is connected to. NOT the actual voltage applied to the battery.
What does changing the setting from low to high on the transformer of a battery charger do?
1) Increases the volts per turn ratio of the primary
2) increases the voltage output of the secondary to the rectifier.
What is the purpose of having two paralleled windings on the secondary of the transformer of a battery charger?
To reduce required secondary winding conductor size. (Provide increased current capacity at lower cost)
What type of parallelled rectifiers are used in the battery charger displayed in the module?
Single phase full wave Center tapped
What is each end of a secondary winding in a battery charger connected to?
On one end, solidly connected to for negative rail
On the other end, connected to the anodes of four press fit diodes
Why do the parallelled diodes on the secondary of a transformer in a battery charger need to be a closely matched pair?
In order to prevent one diode handling more current than the other which would cause it to overheat
What is the advantage of a double winding and diode arrangement for a battery charger?
Increase his reliability if one diode fails
What are other components of battery chargers?
Overcurrent circuit breaker Ammeter Correct polarity indicator Charge time clock Power on indicator lamp
Where are the three paralleled circuit breakers for a battery charger located?
Bolted to the heatsink
How is the ammeter connected in a battery charger?
In series with the output
How is a light emitting diode connected in order to indicate correct polarity of battery connection?
In series with a 220 Ohm resistor and connected across the output
What component does the timer in a battery charger turn off?
The Transformer
Where does the timer in a battery charger draw its power from?
Motor connected across AC input
What internal connection does a power on indicator lab actually represent?
Connection between the ac input and the transformer, through the timer.
How do you change the current setting on a battery charger?
By adjusting the voltage input to the rectifier by
changing the tap on the primary of the Transformer with
a selector switch
Higher voltage to a battery charger causes (higher/lower) current to flow?
Higher
What’s the difference between a 12 volt low and 12 volt high setting on a battery charger?
The output voltage level.
Low setting has a peak of 18 volts
high setting has a peak of 20 volts
What conditions are required in order for charging to actually happen?
charger voltage has to be higher than battery voltage
What is applied to the load for half-wave recifiers?
Every second alternation
What is applied to the load for full wave rectifiers?
Every ac alternation
When does voltage appear across the load in a single-phase half wave recifier?
When the recifier is forward biased
What percentage of peak voltage is the average voltage value of the output of a single phase half wave recifier?
31.8%
Where would a single phase half wave recifier leads be connected for power?
L1 and N
Or
L2 and N
What is the ripple frequency of a single phase half wave recifier?
Equal to supply frequency
