Download Power Supplies

SWITCH-MODE POWER
SUPPLIES AND SYSTEMS
Lecture No 3
Silesian University of Technology
Faculty of Automatic Control, Electronics
and Computer Sciences
Ryszard Siurek Ph.D., El. Eng.
Significant input parameters specified for the
Power Supply
input voltage range (e.g. 230V +10%,-15% or 90V – 260V wide range)
 input voltage type (single phase, three-phase, AC, DC or both)
 input voltage frequency (e.g. 40Hz – 60Hz or 40Hz – 400Hz)
 maximum input RMS current (in worst case)
 inrush current (when switching on) – e.g. 30A (typical value)

IR
IIN
Input current for resistive load
UIN
t
Electro-Magnetic Interference (EMI) emission
Radiated electromagnetic
interference field
(measured in the range of
30 MHz to 1 Ghz)
Supply line
Conducted interference
voltages and currents
(measured in the range of
0,15 MHz to 30 MHz)
Power
Supply
Electromagnetic noise (EMI)

Conducted noise (interference)
- noise voltage measured across 50W resistance in normalized circuit
built in a so called „artificial mains”
- frequency range: 150kHz - 30 MHz
- measurement unit: dBm
ZCN = 20log UN [dBm]
ZCN - conducted noise level
1mV

Radiated noise (interference)
- measurement of electromagnetic field strenght in the air
- frequency range:
30MHz - 1GHz
- measurement unit: dBmV/m
ZRN = 20log EN [dBmV/m) ZRN – radiated noise level
1mV/m
Noise limits and methods of measurement are presented in EN standarts, e.g.:
PN-EN55022 – Information technology equipment. Radio disturbance
characteristics. Limits and methods of measurement.
EMI measurement equipment
Shielded chamber
UIN
IN
Artificial
Power Supply
mains
under test
Ro
EN
Electromagnetic field spectrum
Selective milivoltmeter
analyser
measurement range: 0,15 – 30MHZ
in the range 30MHz – 1GHz
Typical measurement results for
conducted disturbances (interference)
Power Factor
UIN, IIN
U
I
Dt
„total power”
apparent power
2
S [VA] = I Z
f
real power
2
P [W] = I R
T
t
f = 1/T
f = 2pfDt
reactive power
2
Q [var] = I (X L - X C)
PF = cos f
Power Factor
Formulas valid for sinusoidal waveforms
UIN, IIN
I1
I-st harmonic of I1(1)
U
I1(1)RMS
I1RMS
Form Factor
t
Ks =
Dt (f)
P (real power)
total power (apparent) S = I1RMS •U
Uwe, Iwe
I2
U
t
1RMS
PF = S = II2RMS
P
PF = Ks cosf
PF < 1 (0,6 – 0,75)
total power S = I2RMS •U = P real power
Distorted current waveform results in:
apparent power increase (it means higher current consumption from the
mains)
-
more current harmonics in supplying wires which may cause the distortion
of normally sinusoidal voltage waveshape
-
increase of current flow through the neutral conductor in multi-phase power
grids
-
Formal regulations limiting harmonic content in AC supply input current for
electrical and electronic appliances of output power in the range from 75W
to 1000W are effective since the year 2001.
Obligatory standard:
EN 61000-3-2
Electromagnetic Compatibility (EMC) – Limits for harmonic current
emissions (equipment input current up to and including 16A per phase)
Some means should be applied to improve input current shape in Power
Supplies –
Active Power Factor Correction (PFC)
Immunity against external
electromagnetic disturbances
electrostatic discharge
lightning on AC input
conductors (surges)
Power
Supply
fast transients - BURST
(amplitude up to 4 kV)
elctromagnetic
fields
Power supply systems
- safety
Central Power
Supply
UIN
U1
~
~
Load #1
- reliability
Load #2
U2
Un
Batteries
Load # k
Centralized Supply System
- functionality
- cost
Power Supply # 1
~
~
Load # 1
U1
Load # 2
- safety
- functionality
- reliability
Load # 3
- cost
Power Supply # 2
U2
~
~
UPS
UIN
U3
UIN’
~
~
Load # 4
Load # 5
~
~
Load # N
Batteries
Power Supply # N
~
~
Un
Load # N+1
Multiple Centralized Power System
Low power DC-DC
converter
- safety
Load # 1
- functionality
- reliability
- cost
Low power DC-DC
converter
230V
50Hz
~
~
12V - 24V
U1i
Load # 2
U2i
12V - 24V
DC input
switching regulator
with auxilliary outputs
U2n
U1n
Load # N
U3n
Low voltage distributed power supply system
(high voltage distributed power supply system)