310203b Power Supplies

Question 1

What is a rectifier?

Answer 1

A rectifier is an electronic device capable of converting the power supply from single or 3 phase AC to DC

Question 2

What are the three key components of a basic uninterruptible power supply system?

Answer 2

1. The rectifier
2. The DC storage battery
3. The inverter

Question 3

What is an inverter?

Answer 3

An inverter is an electronic circuit that can transform DC input to an AC output

Question 4

Rectifiers are categorized into two groups, what are they?

Answer 4

1. Halfwave-rectifiers, every second AC alternation is applied to the load
2. Full-wave rectifiers, every AC alternation is applied to the load

Question 5

What are the 3 most common single phase rectifiers??

Answer 5

1. Half-wave
2. Full-wave, center tap
3. Full-wave bridge

Question 6

What is the formula for calculating the average voltage output of a half-wave rectifier?

Answer 6

Question 7

How would you calculate the ripple frequency of a single phase full wave rectifier?

Answer 7

For a single phase full wave rectifier, the ripple frequency is 2 times the frequency of the supply voltage.

Question 8

How would you calculate the average load voltage of a single phase full wave rectifier?

Answer 8

Secondary peak voltage x 63.7%

Question 9

Filters smooth out the DC voltage provided by the rectifier in a power supply
What are two typical kinds of devices used in filter circuits?

Answer 9

1. Capacitors
2. Chokes (inductors)

Question 10

Describe the operation of a capacitor filter circuit

Answer 10

A capacitor is connected in parallel with the output terminals of a rectifier and in parallel with the load
A capacitor opposes a change in voltage. When the rectified voltage rises toward the maximum voltage, the capacitor charges. At peak voltage the capacitor stops charging and as the rectifier voltage begins to decrease the capacitor opposes this drop and discharges its energy into the circuit. The capacitor then discharges through the load which reduces the amount of ripple on the load

Question 11

What is the formula for choosing the minimum size of filter capacitor required

Answer 11

Question 12

Define a choke filter

Answer 12

A choke filter is a inductor that can filter the ripple voltage of a rectifier.
The choke filter consists of an inductor coil connected in series with the output of a rectifier and in series with the load.
The coil can have an air core or an iron core.
An inductor tends to oppose a changing current. As the current increases, the inductor opposes the increase, so it lowers the peak values. When the current decreases, the collapsing magnetic field tries to maintain current. This results in a reduced ripple at the load

Question 13

What are the 2 disadvantages of choke filters?

Answer 13

1. The choke filter has virtually no filtering effect when there is little or no load current.
2. The choke coil introduces spikes (noise) into the load. If the load is switched off suddenly depending on the sensitivity of the load, this may be a problem.

Question 14

What is an L-section filter or choke input filter?

Answer 14

L-section filters, also called choke input filters, consist of a capacitor and choke filter.
They are more effective over a wide range of loads than capacitor or choke filters used individually.
The capacitor provides good filtering at small loads, while the choke is more effective with larger loads
The capacitor also suppresses spikes that the choke coil produces when the load current changes rapidly