POWER SUPPILES

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POWER SUPPILES LECTURE 20
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LINEAR POWER SUPPLY
Circuit Skills Power Supply .
http//www.youtube.com/watch?vqPt0X5s-1JU
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SMPS (SWITCH MODE POWER SUPPLY)
Practically all electronic systems require some
form of energy conversion. A device that
transfers electric energy from a given source to
a given load using electronic circuits is
referred to as power supply. Of course, it does
not really supply power, it just converts it, so
"converter" is a more accurate term for such a
device.A typical application of a DC power
supply unit (PSU) is to convert AC voltage into
regulated DC voltages required for electronic
equipment. Original PSUs were linear. Nowadays
most of them are of SMPS type. What is it? The
units in which the energy flow is controlled with
semiconductors that are continuously switching on
and off with high frequency are referred to as
switch mode power supplies or SMPS.
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SMPS offer greater efficiency compared with
linear supplies because a switch can control
energy flow with low losses when a switch is on,
it has low voltage drop and will pass any current
imposed on it when it is off, it blocks the flow
of current. As the result, in such a switch the
power dissipation which is the product of voltage
and current, can be relatively low in both
states. Switching mode units are also smaller in
size and lighter in weight due to the reduced
size of passive components and lower heat
generation.
In general, SMPS can be classified into four
types according to the form of input and output
voltages AC to DC ,DC to DC (voltage or current
converter), AC to AC and DC to AC (inverter).
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SWITCH MODE POWER SUPPLY BLOCK DIAGRAM
http//www.youtube.com/watch?vLf7JJAAZxEU
Circuit Skills PWM (Pulse Width Modulation)
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SMPS power handling electronic components are
continuously switching on and off with high
frequency in order to provide the transfer of
electric energy via energy storage components
(inductors and capacitors). By varying duty
cycle, frequency or a relative phase of these
transitions the average value of output voltage
or current is controlled. The frequency range of
a commercial SMPS units varies typically from 50
kHz to several MHz.
                                                                                                   
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The lowpass EMI filter is designed to reduce high
frequency currents getting from PSU into the AC
line to an acceptable level. This is necessary to
prevent the PSU from causing interference on the
other devices connected to the input wiring.
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The AC is rectified by a full-wave bridge
rectifier. The rectified voltage is next applied
to the power factor correction (PFC)
pre-regulator followed by output DC-DC
converter(s).
TRUE POWER IS THE ACTUAL POWER USED BY THE
CIRCUIT. IT IS MEASURED WITH A WATTMETER. APPARENT
POWER POWER IN A CIRCUIT WHEN VOLTAGE AND
POWER ARE MEASURED SEPARATELY IT IS CALCULATED
IN UNITS OF VOLTAMPERE. (VA)
PF It measures how effectively AC power is being
used by a device.  The difference between true
power and
POWER FACTOR IS THE RATIO OF TRUE POWER/APPARENT
POWER. WHEN CURRENT AND VOLTAGE ARE IN PHASE THE
POWER FACTOR 1. IF 90 OUT OF PHASE THE POWER
FACTOR 0. POWER FACTOR OF A CIRCUIT CAN VARY
BETWEEN O AND 1.
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The rectified input voltage is next fed into
(PFC) stage, which increases power factor (PF).
In the process it usually boosts the voltage to a
regulated 370-400 VDC. PF by definition is the
ratio between watts and volt-amps. A PFC
pre-regulator controls input AC current so that
it is in phase with mains AC voltage and its
waveform repeats the input voltage waveform.
Without this, the input current would be
delivered to the SMPS in short high peak pulses,
which have a high harmonic content. The current
harmonics do not supply any real power to the
load, but cause additional heating in the wiring
and distribution equipment. They also reduce the
maximum amount of electricity that can be taken
from a standard wall outlet, since home circuit
breakers are rated by current rather than by
watts..
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Locating the primary and the secondary.
SMPS Repair
http//www.youtube.com/watch?vv7nTAQOdT-Y
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Transient filter second stage.
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Electrolytic capacitors from the voltage doubler.
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Rectifying bridge.
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Active POWER FACTOR CORRECTION components.
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Components attached to the primary heatsink.
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Power supply transformers.
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PWM control circuit.
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Power supply secondary stage.
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Rectifying diodes for the 12 V and 5V lines.
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Components found on the secondary heatsink of a
high-end power supply.
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This power supply uses optocouplers instead of
using a transformer to isolate the PWM circuit.