1
Q
What is a half-wave rectifier?
A
- The diode will convert input voltage (Vin) waveform into half wave output (Vout).
- Input Frequency = Output Frequency
- Only the positive half-cycles appear across the load
- V(out) = V(in) - 0.7V
- V(avg) = Vp/ π
- PIV = V(in)
A transformer is often used:
* It allows the source voltage to be stepped up or down as needed
* The ac source is electrically isolated from the rectifier, thus preventing a shock hazard in the secondary
2
Q
What is a full-wave centre-tapped rectifier?
A
- Most commonly used type in dc power supplies
- Allows unidirectional (one-way) current to the load during the entire input cycle
- Output frequency is twice that of input frequency
- Current through the load resistor is in the same direction during the entire input cycle, so the output voltage always has the same polarity
- Vp(out)= [ Vp(sec) / 2 ] - 0.7V
- V(avg) = 2Vp(out)/ π
- PIV = 2Vp(out) + 0.7V
3
Q
What is a full-bridge rectifier?
A
- Circuit uses four diodes
- Two diodes are always in series with the load resistor during both half-cycles
- Vp(out) = V(sec) - 1.4V
- V(avg) = 2Vp(out)/ π
- PIV = Vp(out) + 0.7V
4
Q
What is a Capacitor Filter?
A
- A Capacitor filter eliminates (or reduces) fluctuations in output voltage of a rectifier and It produces a (near) constant-level dc voltage
- The capacitor charges at the beginning of each cycle (positive first-quarter)
- It slowly discharges through load after the positive peak (when diode is reverse-biased)
- The smaller the ripple, the better the filtering action is.
- The ripple factor can be lowered by increasing the value of the filter capacitor or increasing the load resistance
- r = V(rms) / V(dc/avg) // of ripple voltage
5
Q
What are the components in a DC power supply?
A
- Transformer - steps down the ac voltage at the primary
- Rectifiers - convert ac voltage into dc voltage
- Filter – eliminates the fluctuations in the rectified voltage and produces a relatively smooth dc voltage
- Voltage regulator - maintains a constant dc voltage for variations in the input line voltage or in the load
- Load – a circuit for which the power supply is producing the dc voltage and load current
6
Q
What does a voltage regulator do?
A
- The main function of a voltage regulator is to maintain constant output voltage when:
(a) its input voltage changes
(b) the load connected to it changes - Line regulation maintains a nearly constant output voltage when the input voltage varies. Line Regulation = [ΔV(out) / ΔV(in)] x 100%
- Load regulation maintains a nearly constant output voltage when the load varies. Load regulation = [(V(no load) - V(full load)) / V(fl)] x 100%
7
Q
How to identify voltage regulators?
A
- The three terminals are input, output, and ground.
- The last two digits in the part number designate the
output voltage. - The 7800 and 7900 series regulators provide fixed-value positive and negative output voltages respectively.
- The output capacitor acts basically as a line filter to improve transient response.
- The input capacitor is used to prevent unwanted oscillations when the regulator is some distance from the power supply filter such that the line has high inductance
8
Q
What are diode limiting circuits?
A
- Diode limiting circuits (also called limiters orclippers) are used to clip off portions of signal voltages above or below certain levels
