Download TYPES OF POWER SUPPLY

1.0 LINEAR DC POWER SUPPLY
1.1.1 The importance of DC Power Supply Circuit
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For electronic circuits made up of transistors and/or ICs, this
power source must be a DC voltage of a specific value.
Dry cells is not economical because the electronic equipment
that requires high voltage use a lot of dry cells.
A battery is a common DC voltage source for some types of
electronic equipment especially portables like cell phones and
iPods.
Most are designed to convert high voltage AC mains electricity
to a suitable low voltage supply for electronics circuits and
other devices.
Incoming power supply from TNB is in alternating current and
high voltage ( 1 phase = 240 V, 3 phase = 415V)
1.1.2 BLOCK DIAGRAM OF DC POWER SUPPLY
Schematic Diagrams Of a Simple
Power Supply
Rectifier
circuit
1.1.3 The Function of each Block
Transformer circuit symbol
1.1.1 Transformer
• Transformer convert AC electricity from one
voltage to another with little loss of power.
Transformers work only with AC and this is one
of the reasons why mains electricity is AC.
• Step-up transformers increase voltage, stepdown transformers reduce voltage. Most power
supplies use a step-down transformer to reduce
the dangerously high mains voltage (230V in
UK) to a safer low voltage.
• The input coil is called the primary and the
output coil is called the secondary. There is no
electrical connection between the two coils,
instead they are linked by an alternating
magnetic field created in the soft-iron core of the
transformer. The two lines in the middle of the
circuit symbol represent the core.
• Transformers waste very little power so the
power out is (almost) equal to the power in. Note
that as voltage is stepped down current is
stepped up.
Transformer:Turn Ratio
• The ratio of the number of turns on each coil, called the
turns ratio, determines the ratio of the voltages. A stepdown transformer has a large number of turns on its
primary (input) coil which is connected to the high
voltage mains supply, and a small number of turns on its
secondary (output) coil to give a low output voltage.
Transformer only
• The low voltage AC output is suitable for lamps, heaters
and special AC motors. It is not suitable for electronic
circuits unless they include a rectifier and a smoothing
capacitor.
Transformer + Rectifier
• The varying DC output is suitable for lamps,
heaters and standard motors. It is not suitable
for electronic circuits unless they include a
smoothing capacitor.
Transformer + Rectifier +
Smoothing
• The smooth DC output has a small ripple.
It is suitable for most electronic circuits.
Transformer + Rectifier + Smoothing +
Regulator
The regulated DC output is very smooth with no
ripple. It is suitable for all electronic circuits.
1.2 Rectifier
Most of the devices in electronic system need
the dc power supply to operate.
• Source of the power that supplied to our home is
AC.
• To get DC voltage, we use the rectifier circuit.
Rectifier is the circuit that used 1/more than 1
diode to convert the AC volt to the pulsating
voltage.
• There are 3 types of rectifier:
1) Half Wave Rectifier
2) Full Wave Rectifier
3) Bridge Rectifier
1.21 Half Wave Rectifier
• The arrow on the diode
indicates the
direction of the current in the diode
• Because of the diode, the alternating current in
the load resistor is reduced to the positive
portion of the cycle
1.2.2 Operation of Half waveRectifiers
• During the positive cycle of the input signal, the diode D
forward bias. D acts as a switch is closed the current
can pass through. Voltage drop on the RL is equal to the
magnitude of the positive cycle if we ignore the input
signal voltage drop on the diode.
1.2.2 Operation of Half waveRectifiers
• During the negative cycle of input signal, the diode D
reverse biased. D acts as a switch is open so current
can not pass through. Voltage drop in the RL during the
negative cycle is empty.
1.2.3:The input & Output Waveform
• Plot of Input Vi & Output Vo waveform for half-wave
rectifier ideal diode
Output Voltage
Output voltage for half-wave rectifier circuit current
produced only positive cycle. Since the current through
the diode and the diode voltage drop is 0.7V (assuming
silicon diode), the output voltage is: Vout = Vin – 0.7V
Frequency
The frequency output signal is equal to the input
frequency.
Example 1:
A half-wave rectifier circuit for input voltage 20 Vp-p,
50 Hz. By making the assumption there is no voltage
drop on the diode, calculate: i) Rectifier output voltage signal
Vin = 20 Vp-p
Vp = 10 Vp
 Vout = 10 Vp
ii) Frequency of the output signal
Output frequency = Input frequency signal
= 50 Hz
Example 2:
Calculate the peak output voltage and peak current
flowing through the diode during the forward biased
state.
Answer:
Peak output voltage, Vp (out) = 5 – 0.7 = 4.3V
Peak current, Ip = Vp (out) / R = 4.3 / 47 = 91.5mA
1.3 Full-Wave Rectifiers
1.3.1 Full-Wave Rectifier Circuit
with Center Tap Transformer
1.3.2 Operation Of the Circuits
• During positive cycle of Vin, D1 is forward-biased and D2
is reverse-biased
FIGURE 1.3.2 (a)
• During negative cycle of the input, the network appears
as shown in FIGURE 1.3.2 (b), reversing the role of the
diodes, D2 is forward biased & D1 is reverse biased. The
net effect is same output as the appearing in FIGURE
1.3.2 (a)
FIGURE 1.3.2 (b)
Input & Output Waveform Of Full-Wave
Rectifier
Figure 1.3.2 ( C ):Waveform of Full-Wave rectifier
1.4 Bridge Rectifier
• 1.4.1 Full-Wave Bridge rectifier Circuit
Figure 1.4.1 (a)
When we connect the oscilloscope across the RL we
will find the output waveform is the same as figure
1.4.1 (a)
1.4.2 The operation circuit of Bridge
Rectifier
• Positive Half-cycle
1.4.2 The operation circuit of Bridge
Rectifier
• Negative Half-cycle
1.4.2 The operation circuit of Bridge
Rectifier-contd
Output Voltage
• Output voltage of full wave bridge rectifier circuit
resulting in two cycles.
• Since in a cycle of current through the two
diodes and the voltage drop on the diode is 1.4V
(assuming silicon diode), the output voltage is:
Vo = VM-N – 1.4V
Frequency
• Frequency output signal is twice frequencies
input.
1.5 & 1.6:Types of filter
There are 4 types of general filter are used:
1) Capacitor filter
2) RC filter
3) LC filter
4)  filter
1) The operation of capacitor filter
diagram
1.5.1 The operation and filtering process of RC filter
circuits using O/P wave (half-Wave)
The operation and filtering process of
Capacitor filter circuits using O/P wave
(half-Wave)-contd
• During the first cycle, the capacitor charges from
points A to B reaching the maximum voltage, Vmax.
• Between points B and C, when the input voltage is
less than Vmax, the capacitor starts discharging
through the resistor, RL.
• The capacitor will discharge until point C during
which the input voltage is equal to the capacitor
voltage and the capacitor starts to charge again.
• This process is repeated for the next cycle.
1.5.2 Ripple Voltage
•
Definition: A small variation
occurs in the DC because the
capacitor discharges a small
amount between the positive
and negative pulses. Then it
recharges. This variation is
called ripple.
•
The ripple can be reduced
further by making the capacitor
larger.
•
The ripple appears to be a
sawtooth shaped AC variation
riding on the DC output.
•
A small amount of ripple can be
tolerated in some circuits but
the lower the better overall.
Types of filter-CONTD
2) RC Filter
 RC filter is added after the filter capacitor.
 RC filters are produced : a resistor in series with the
load (RL) and a capacitor in parallel with (RL).
Effects of RC filter
 Resistor (R) will decrease the voltage ripple.
 C2 will filter the balance of the ripple voltage.
Types of filter-CONTD
3) LC Filter
LC filters have been produced by
combination inductor in series and capacitor in
parallel.
The inductor, L function is to reduce the
ripple even more without a lot of dc resistance.
Provided the ripple reduction is sufficient
and the power loss in the resistor is not
excessive.
Types of filter-CONTD
4)  filter



 filter acts to overcome the problems generated by the RC filter.
Resistor in the RC filter is replaced with the inductor (L).
The filtering action of each component:
 C1 : - low reactance to AC
- infinite resistance to DC
- bypass AC to ground while DC moved towards L
 L : - high reactance to AC
- zero resistance to DC
- allows DC to pass through it and blocks AC
 C2 : - similar to C1
- bypass AC which could not blocked by L
- only DC available at the output
1.7 The operation of voltage
regulator circuit
1.7 Voltage Regulation
The function of a voltage regulator is to:
a) Stabilize the output voltage even though there is a
variation of the input current or output current.
b) Reduce the ripple at the output voltage of the filter
circuit.
There are three types of voltage regulator circuit : -
1) Voltage regulator zener diode
2) Transistor series voltage regulator
3) Voltage regulator integrated circuit (78XX series)
1.7.1 (a) Zener Diode
• Basic Zener diode regulator circuit is shown in figure below.
• This is a type of shunt regulator. In designing such a circuit, one has
to know the value of the series resistor, Rs, the maximum current
that the Zener diode will have to handle, the variation of the input
voltage, Vin, and the variation of the load current, IL.
• For variations in Vin, the Zener circuit maintains constant voltage,
Vo, across the load, RL, by changing the current through the series
resistor Rs.
1.7.1 (b) Serial Transistor
• Transistors connected in series with the load will control the input
voltage to output. Referring to figure below, if the output voltage
decreases, the increase in the VBE will cause the transistor to
produce more than the current flow will increase the output voltage
and maintain the output voltage. The zener diode will act as a
reference voltage. The same process occurs if the output voltage
increases. The transistor will reduce the current value, causing the
output voltage and maintaining the output voltage decreases
FIGURE 1.71.b: Simple types of series regulator using a Zener diode and a
transistor
1.7.1 (b) Serial Transistor-CONTD
• The Zener diode will keep the base voltage constant
while the transistor forms a variable series resistor.
Since the emitter is always 0.7 V or so different from
the base voltage, a constant output voltage will result.
The transistor amplifies the effect of the Zener diode,
so not only will better regulation result, but higher
current can be drawn with less power dissipation than
the equivalent shunt regulator.
1.7.1 (c )Integrated Circuits
• LM Series 78XX (where XX = 05, 06, 08, 10, 12, 15, 18
or 24) is a three-terminal voltage regulator. IC LM7805
will produce output voltage +5 V, the LM7806 will
produce +6 V output voltage and thus LM7824 will
produce output voltage +24 V.
• Figure 1.7.1 (c ) shows the integrated circuit voltage
regulator circuit.
1.7.1 (c) Integrated Circuits
• The pulsating DC input voltage from the rectifier
is filtered by the capacitor, C1 which filters the
undesired ripples before it is connected to
terminal 1.
• The regulated output voltage of +5V is produced
at terminal 2 filter by the capacitor C2.
• C2 will also filter all the high frequency distortion
in the system.
• Terminal 3 is grounded.
1.8 Voltage Divider Circuits
• In some systems of electronic equipment,
especially equipment large or complex, it
consists of several stages, each circuit is
sometimes used voltages at different value.
• For example TV system, there are more than ten
different levels of circuit functions and some that
require voltage 100V, 48V, 12V and ect.
• By using DC power supply, it can be
accomplished by having the voltage divider
network after a high voltage value has been
obtained.
1.8.1 Voltage Divider CircuitsContd
1.9 Schematic Diagrams Of a
Simple Power Supply
Rectifier
circuit
1.9 Schematic Diagrams Of a
Simple Power Supply
• Figure 1.9a shows schematic diagrams of a
simple power supply. From left to right, we find
the center tap transformer will reduce the ac
supply voltage. The full-wave rectifier converts
ac voltage to DC.
•  filters are used to ensure the DC voltage are
pulsed and then the DC will be stabilize by zener
diode.